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C user guide clean up. Up to timer manager.

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c_user/clock_manager.rst
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@ -1,3 +1,7 @@
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
Clock Manager
#############
@ -10,37 +14,37 @@ The clock manager provides support for time of day
and other time related capabilities. The directives provided by
the clock manager are:
- ``rtems_clock_set`` - Set date and time
- rtems_clock_set_ - Set date and time
- ``rtems_clock_get`` - Get date and time information
- rtems_clock_get_ - Get date and time information
- ``rtems_clock_get_tod`` - Get date and time in TOD format
- rtems_clock_get_tod_ - Get date and time in TOD format
- ``rtems_clock_get_tod_timeval`` - Get date and time in timeval format
- rtems_clock_get_tod_timeval_ - Get date and time in timeval format
- ``rtems_clock_get_seconds_since_epoch`` - Get seconds since epoch
- rtems_clock_get_seconds_since_epoch_ - Get seconds since epoch
- ``rtems_clock_get_ticks_per_second`` - Get ticks per second
- rtems_clock_get_ticks_per_second_ - Get ticks per second
- ``rtems_clock_get_ticks_since_boot`` - Get current ticks counter value
- rtems_clock_get_ticks_since_boot_ - Get current ticks counter value
- ``rtems_clock_tick_later`` - Get tick value in the future
- rtems_clock_tick_later_ - Get tick value in the future
- ``rtems_clock_tick_later_usec`` - Get tick value in the future in microseconds
- rtems_clock_tick_later_usec_ - Get tick value in the future in microseconds
- ``rtems_clock_tick_before`` - Is tick value is before a point in time
- rtems_clock_tick_before_ - Is tick value is before a point in time
- ``rtems_clock_get_uptime`` - Get time since boot
- rtems_clock_get_uptime_ - Get time since boot
- ``rtems_clock_get_uptime_timeval`` - Get time since boot in timeval format
- rtems_clock_get_uptime_timeval_ - Get time since boot in timeval format
- ``rtems_clock_get_uptime_seconds`` - Get seconds since boot
- rtems_clock_get_uptime_seconds_ - Get seconds since boot
- ``rtems_clock_get_uptime_nanoseconds`` - Get nanoseconds since boot
- rtems_clock_get_uptime_nanoseconds_ - Get nanoseconds since boot
- ``rtems_clock_set_nanoseconds_extension`` - Install the nanoseconds since last tick handler
- rtems_clock_set_nanoseconds_extension_ - Install the nanoseconds since last tick handler
- ``rtems_clock_tick`` - Announce a clock tick
- rtems_clock_tick_ - Announce a clock tick
Background
==========
@ -48,93 +52,89 @@ Background
Required Support
----------------
For the features provided by the clock manager to be
utilized, periodic timer interrupts are required. Therefore, a
real-time clock or hardware timer is necessary to create the
timer interrupts. The ``rtems_clock_tick``
directive is normally called
by the timer ISR to announce to RTEMS that a system clock tick
has occurred. Elapsed time is measured in ticks. A tick is
defined to be an integral number of microseconds which is
specified by the user in the Configuration Table.
For the features provided by the clock manager to be utilized, periodic timer
interrupts are required. Therefore, a real-time clock or hardware timer is
necessary to create the timer interrupts. The ``rtems_clock_tick`` directive
is normally called by the timer ISR to announce to RTEMS that a system clock
tick has occurred. Elapsed time is measured in ticks. A tick is defined to be
an integral number of microseconds which is specified by the user in the
Configuration Table.
Time and Date Data Structures
-----------------------------
The clock facilities of the clock manager operate
upon calendar time. These directives utilize the following date
and time structure for the native time and date format:
The clock facilities of the clock manager operate upon calendar time. These
directives utilize the following date and time structure for the native time
and date format:
.. index:: rtems_time_of_day
.. code:: c
struct rtems_tod_control {
uint32_t year; /* greater than 1987 \*/
uint32_t month; /* 1 - 12 \*/
uint32_t day; /* 1 - 31 \*/
uint32_t hour; /* 0 - 23 \*/
uint32_t minute; /* 0 - 59 \*/
uint32_t second; /* 0 - 59 \*/
uint32_t ticks; /* elapsed between seconds \*/
uint32_t year; /* greater than 1987 */
uint32_t month; /* 1 - 12 */
uint32_t day; /* 1 - 31 */
uint32_t hour; /* 0 - 23 */
uint32_t minute; /* 0 - 59 */
uint32_t second; /* 0 - 59 */
uint32_t ticks; /* elapsed between seconds */
};
typedef struct rtems_tod_control rtems_time_of_day;
The native date and time format is the only format
supported when setting the system date and time using the``rtems_clock_set`` directive. Some applications
expect to operate on a "UNIX-style" date and time data structure. The``rtems_clock_get_tod_timeval`` always returns
the date and time in ``struct timeval`` format. The``rtems_clock_get`` directive can optionally return
the current date and time in this format.
The native date and time format is the only format supported when setting the
system date and time using the ``rtems_clock_set`` directive. Some
applications expect to operate on a *UNIX-style* date and time data structure.
The ``rtems_clock_get_tod_timeval`` always returns the date and time in
``struct timeval`` format. The ``rtems_clock_get`` directive can optionally
return the current date and time in this format.
The ``struct timeval`` data structure has two fields: ``tv_sec``
and ``tv_usec`` which are seconds and microseconds, respectively.
The ``tv_sec`` field in this data structure is the number of seconds
since the POSIX epoch of January 1, 1970 but will never be prior to
the RTEMS epoch of January 1, 1988.
The ``struct timeval`` data structure has two fields: ``tv_sec`` and
``tv_usec`` which are seconds and microseconds, respectively. The ``tv_sec``
field in this data structure is the number of seconds since the POSIX epoch of
*January 1, 1970* but will never be prior to the RTEMS epoch of *January 1,
1988*.
Clock Tick and Timeslicing
--------------------------
.. index:: timeslicing
Timeslicing is a task scheduling discipline in which
tasks of equal priority are executed for a specific period of
time before control of the CPU is passed to another task. It is
also sometimes referred to as the automatic round-robin
scheduling algorithm. The length of time allocated to each task
is known as the quantum or timeslice.
Timeslicing is a task scheduling discipline in which tasks of equal priority
are executed for a specific period of time before control of the CPU is passed
to another task. It is also sometimes referred to as the automatic round-robin
scheduling algorithm. The length of time allocated to each task is known as
the quantum or timeslice.
The system's timeslice is defined as an integral
number of ticks, and is specified in the Configuration Table.
The timeslice is defined for the entire system of tasks, but
timeslicing is enabled and disabled on a per task basis.
The system's timeslice is defined as an integral number of ticks, and is
specified in the Configuration Table. The timeslice is defined for the entire
system of tasks, but timeslicing is enabled and disabled on a per task basis.
The ``rtems_clock_tick``
directive implements timeslicing by
decrementing the running task's time-remaining counter when both
timeslicing and preemption are enabled. If the task's timeslice
has expired, then that task will be preempted if there exists a
ready task of equal priority.
The ``rtems_clock_tick`` directive implements timeslicing by decrementing the
running task's time-remaining counter when both timeslicing and preemption are
enabled. If the task's timeslice has expired, then that task will be preempted
if there exists a ready task of equal priority.
Delays
------
.. index:: delays
A sleep timer allows a task to delay for a given
interval or up until a given time, and then wake and continue
execution. This type of timer is created automatically by the``rtems_task_wake_after``
and ``rtems_task_wake_when`` directives and, as a result,
does not have an RTEMS ID. Once activated, a sleep timer cannot
be explicitly deleted. Each task may activate one and only one
sleep timer at a time.
A sleep timer allows a task to delay for a given interval or up until a given
time, and then wake and continue execution. This type of timer is created
automatically by the ``rtems_task_wake_after`` and ``rtems_task_wake_when``
directives and, as a result, does not have an RTEMS ID. Once activated, a
sleep timer cannot be explicitly deleted. Each task may activate one and only
one sleep timer at a time.
Timeouts
--------
.. index:: timeouts
Timeouts are a special type of timer automatically
created when the timeout option is used on the``rtems_message_queue_receive``,``rtems_event_receive``,``rtems_semaphore_obtain`` and``rtems_region_get_segment`` directives.
Each task may have one and only one timeout active at a time.
When a timeout expires, it unblocks the task with a timeout status code.
Timeouts are a special type of timer automatically created when the timeout
option is used on the ``rtems_message_queue_receive``, ``rtems_event_receive``,
``rtems_semaphore_obtain`` and ``rtems_region_get_segment`` directives. Each
task may have one and only one timeout active at a time. When a timeout
expires, it unblocks the task with a timeout status code.
Operations
==========
@ -142,71 +142,67 @@ Operations
Announcing a Tick
-----------------
RTEMS provides the ``rtems_clock_tick`` directive which is
called from the user's real-time clock ISR to inform RTEMS that
a tick has elapsed. The tick frequency value, defined in
microseconds, is a configuration parameter found in the
Configuration Table. RTEMS divides one million microseconds
(one second) by the number of microseconds per tick to determine
the number of calls to the``rtems_clock_tick`` directive per second. The
frequency of ``rtems_clock_tick``
calls determines the resolution
(granularity) for all time dependent RTEMS actions. For
example, calling ``rtems_clock_tick``
ten times per second yields a higher
resolution than calling ``rtems_clock_tick``
two times per second. The ``rtems_clock_tick``
directive is responsible for maintaining both
calendar time and the dynamic set of timers.
RTEMS provides the ``rtems_clock_tick`` directive which is called from the
user's real-time clock ISR to inform RTEMS that a tick has elapsed. The tick
frequency value, defined in microseconds, is a configuration parameter found in
the Configuration Table. RTEMS divides one million microseconds (one second)
by the number of microseconds per tick to determine the number of calls to
the``rtems_clock_tick`` directive per second. The frequency of
``rtems_clock_tick`` calls determines the resolution (granularity) for all time
dependent RTEMS actions. For example, calling ``rtems_clock_tick`` ten times
per second yields a higher resolution than calling ``rtems_clock_tick`` two
times per second. The ``rtems_clock_tick`` directive is responsible for
maintaining both calendar time and the dynamic set of timers.
Setting the Time
----------------
The ``rtems_clock_set`` directive allows a task or an ISR to
set the date and time maintained by RTEMS. If setting the date
and time causes any outstanding timers to pass their deadline,
then the expired timers will be fired during the invocation of
the ``rtems_clock_set`` directive.
The ``rtems_clock_set`` directive allows a task or an ISR to set the date and
time maintained by RTEMS. If setting the date and time causes any outstanding
timers to pass their deadline, then the expired timers will be fired during the
invocation of the ``rtems_clock_set`` directive.
Obtaining the Time
------------------
The ``rtems_clock_get`` directive allows a task or an ISR to
obtain the current date and time or date and time related
information. The current date and time can be returned in
either native or UNIX-style format. Additionally, the
application can obtain date and time related information such as
the number of seconds since the RTEMS epoch, the number of ticks
since the executive was initialized, and the number of ticks per
second. The information returned by the``rtems_clock_get`` directive is
dependent on the option selected by the caller. This
is specified using one of the following constants
associated with the enumerated type``rtems_clock_get_options``:.. index:: rtems_clock_get_options
The ``rtems_clock_get`` directive allows a task or an ISR to obtain the current
date and time or date and time related information. The current date and time
can be returned in either native or *UNIX-style* format. Additionally, the
application can obtain date and time related information such as the number of
seconds since the RTEMS epoch, the number of ticks since the executive was
initialized, and the number of ticks per second. The information returned by
the``rtems_clock_get`` directive is dependent on the option selected by the
caller. This is specified using one of the following constants associated with
the enumerated type ``rtems_clock_get_options``:
- ``RTEMS_CLOCK_GET_TOD`` - obtain native style date and time
.. index:: rtems_clock_get_options
- ``RTEMS_CLOCK_GET_TIME_VALUE`` - obtain UNIX-style
date and time
``RTEMS_CLOCK_GET_TOD``
obtain native style date and time
- ``RTEMS_CLOCK_GET_TICKS_SINCE_BOOT`` - obtain number of ticks
since RTEMS was initialized
``RTEMS_CLOCK_GET_TIME_VALUE``
obtain *UNIX-style* date and time
- ``RTEMS_CLOCK_GET_SECONDS_SINCE_EPOCH`` - obtain number
of seconds since RTEMS epoch
``RTEMS_CLOCK_GET_TICKS_SINCE_BOOT``
obtain number of ticks since RTEMS was initialized
- ``RTEMS_CLOCK_GET_TICKS_PER_SECOND`` - obtain number of clock
ticks per second
``RTEMS_CLOCK_GET_SECONDS_SINCE_EPOCH``
obtain number of seconds since RTEMS epoch
Calendar time operations will return an error code if
invoked before the date and time have been set.
``RTEMS_CLOCK_GET_TICKS_PER_SECOND``
obtain number of clock ticks per second
Calendar time operations will return an error code if invoked before the date
and time have been set.
Directives
==========
This section details the clock manager's directives.
A subsection is dedicated to each of this manager's directives
and describes the calling sequence, related constants, usage,
and status codes.
This section details the clock manager's directives. A subsection is dedicated
to each of this manager's directives and describes the calling sequence,
related constants, usage, and status codes.
.. _rtems_clock_set:
CLOCK_SET - Set date and time
-----------------------------
@ -220,42 +216,51 @@ CLOCK_SET - Set date and time
.. code:: c
rtems_status_code rtems_clock_set(
rtems_time_of_day \*time_buffer
rtems_time_of_day *time_buffer
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - date and time set successfully
``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL
``RTEMS_INVALID_CLOCK`` - invalid time of day
``RTEMS_SUCCESSFUL``
date and time set successfully
``RTEMS_INVALID_ADDRESS``
``time_buffer`` is NULL
``RTEMS_INVALID_CLOCK``
invalid time of day
**DESCRIPTION:**
This directive sets the system date and time. The
date, time, and ticks in the time_buffer structure are all
range-checked, and an error is returned if any one is out of its
valid range.
This directive sets the system date and time. The date, time, and ticks in the
time_buffer structure are all range-checked, and an error is returned if any
one is out of its valid range.
**NOTES:**
Years before 1988 are invalid.
The system date and time are based on the configured
tick rate (number of microseconds in a tick).
The system date and time are based on the configured tick rate (number of
microseconds in a tick).
Setting the time forward may cause a higher priority
task, blocked waiting on a specific time, to be made ready. In
this case, the calling task will be preempted after the next
clock tick.
Setting the time forward may cause a higher priority task, blocked waiting on a
specific time, to be made ready. In this case, the calling task will be
preempted after the next clock tick.
Re-initializing RTEMS causes the system date and time
to be reset to an uninitialized state. Another call to``rtems_clock_set`` is required to re-initialize
the system date and time to application specific specifications.
Re-initializing RTEMS causes the system date and time to be reset to an
uninitialized state. Another call to ``rtems_clock_set`` is required to
re-initialize the system date and time to application specific specifications.
.. _rtems_clock_get:
CLOCK_GET - Get date and time information
-----------------------------------------
.. index:: obtain the time of day
.. warning::
This directive is deprecated and will be removed.
**CALLING SEQUENCE:**
.. index:: rtems_clock_get
@ -263,49 +268,62 @@ CLOCK_GET - Get date and time information
.. code:: c
rtems_status_code rtems_clock_get(
rtems_clock_get_options option,
void \*time_buffer
rtems_clock_get_options option,
void *time_buffer
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - current time obtained successfully
``RTEMS_NOT_DEFINED`` - system date and time is not set
``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL
``RTEMS_SUCCESSFUL``
current time obtained successfully
``RTEMS_NOT_DEFINED``
system date and time is not set
``RTEMS_INVALID_ADDRESS``
``time_buffer`` is NULL
**DESCRIPTION:**
This directive is deprecated.
This directive obtains the system date and time. If the caller is attempting
to obtain the date and time (i.e. option is set to either
``RTEMS_CLOCK_GET_SECONDS_SINCE_EPOCH``, ``RTEMS_CLOCK_GET_TOD``, or
``RTEMS_CLOCK_GET_TIME_VALUE``) and the date and time has not been set with a
previous call to ``rtems_clock_set``, then the ``RTEMS_NOT_DEFINED`` status
code is returned. The caller can always obtain the number of ticks per second
(option is ``RTEMS_CLOCK_GET_TICKS_PER_SECOND``) and the number of ticks since
the executive was initialized option is ``RTEMS_CLOCK_GET_TICKS_SINCE_BOOT``).
This directive obtains the system date and time. If
the caller is attempting to obtain the date and time (i.e.
option is set to either ``RTEMS_CLOCK_GET_SECONDS_SINCE_EPOCH``,``RTEMS_CLOCK_GET_TOD``, or``RTEMS_CLOCK_GET_TIME_VALUE``) and the date and time
has not been set with a previous call to``rtems_clock_set``, then the``RTEMS_NOT_DEFINED`` status code is returned.
The caller can always obtain the number of ticks per second (option is``RTEMS_CLOCK_GET_TICKS_PER_SECOND``) and the number of
ticks since the executive was initialized option is``RTEMS_CLOCK_GET_TICKS_SINCE_BOOT``).
The ``option`` argument may taken on any value of the enumerated type
``rtems_clock_get_options``. The data type expected for``time_buffer`` is
based on the value of ``option`` as indicated below:
The ``option`` argument may taken on any value of the enumerated
type ``rtems_clock_get_options``. The data type expected for``time_buffer`` is based on the value of ``option`` as
indicated below:.. index:: rtems_clock_get_options
.. index:: rtems_clock_get_options
- ``RTEMS_CLOCK_GET_TOD`` - (rtems_time_of_day \*)
- ``RTEMS_CLOCK_GET_SECONDS_SINCE_EPOCH`` - (rtems_interval \*)
- ``RTEMS_CLOCK_GET_TICKS_SINCE_BOOT`` - (rtems_interval \*)
- ``RTEMS_CLOCK_GET_TICKS_PER_SECOND`` - (rtems_interval \*)
- ``RTEMS_CLOCK_GET_TIME_VALUE`` - (struct timeval \*)
+-----------------------------------------+---------------------------+
| Option | Return type |
+=========================================+===========================+
| ``RTEMS_CLOCK_GET_TOD`` | ``(rtems_time_of_day *)`` |
+-----------------------------------------+---------------------------+
| ``RTEMS_CLOCK_GET_SECONDS_SINCE_EPOCH`` | ``(rtems_interval *)`` |
+-----------------------------------------+---------------------------+
| ``RTEMS_CLOCK_GET_TICKS_SINCE_BOOT`` | ``(rtems_interval *)`` |
+-----------------------------------------+---------------------------+
|``RTEMS_CLOCK_GET_TICKS_PER_SECOND`` | ``(rtems_interval *)`` |
+-----------------------------------------+---------------------------+
| ``RTEMS_CLOCK_GET_TIME_VALUE`` | ``(struct timeval *)`` |
+-----------------------------------------+---------------------------+
**NOTES:**
This directive is callable from an ISR.
This directive will not cause the running task to be
preempted. Re-initializing RTEMS causes the system date and
time to be reset to an uninitialized state. Another call to``rtems_clock_set`` is required to re-initialize the
system date and time to application specific specifications.
This directive will not cause the running task to be preempted.
Re-initializing RTEMS causes the system date and time to be reset to an
uninitialized state. Another call to ``rtems_clock_set`` is required to
re-initialize the system date and time to application specific specifications.
.. _rtems_clock_get_tod:
CLOCK_GET_TOD - Get date and time in TOD format
-----------------------------------------------
@ -318,28 +336,36 @@ CLOCK_GET_TOD - Get date and time in TOD format
.. code:: c
rtems_status_code rtems_clock_get_tod(
rtems_time_of_day \*time_buffer
rtems_time_of_day *time_buffer
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - current time obtained successfully
``RTEMS_NOT_DEFINED`` - system date and time is not set
``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL
``RTEMS_SUCCESSFUL``
current time obtained successfully
``RTEMS_NOT_DEFINED``
system date and time is not set
``RTEMS_INVALID_ADDRESS``
``time_buffer`` is NULL
**DESCRIPTION:**
This directive obtains the system date and time. If the date and time
has not been set with a previous call to``rtems_clock_set``, then the``RTEMS_NOT_DEFINED`` status code is returned.
This directive obtains the system date and time. If the date and time has not
been set with a previous call to ``rtems_clock_set``, then the
``RTEMS_NOT_DEFINED`` status code is returned.
**NOTES:**
This directive is callable from an ISR.
This directive will not cause the running task to be
preempted. Re-initializing RTEMS causes the system date and
time to be reset to an uninitialized state. Another call to``rtems_clock_set`` is required to re-initialize the
system date and time to application specific specifications.
This directive will not cause the running task to be preempted.
Re-initializing RTEMS causes the system date and time to be reset to an
uninitialized state. Another call to ``rtems_clock_set`` is required to
re-initialize the system date and time to application specific specifications.
.. _rtems_clock_get_tod_timeval:
CLOCK_GET_TOD_TIMEVAL - Get date and time in timeval format
-----------------------------------------------------------
@ -351,29 +377,37 @@ CLOCK_GET_TOD_TIMEVAL - Get date and time in timeval format
.. code:: c
rtems_status_code rtems_clock_get_tod(
struct timeval \*time
rtems_status_code rtems_clock_get_tod_interval(
struct timeval *time
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - current time obtained successfully
``RTEMS_NOT_DEFINED`` - system date and time is not set
``RTEMS_INVALID_ADDRESS`` - ``time`` is NULL
``RTEMS_SUCCESSFUL``
current time obtained successfully
``RTEMS_NOT_DEFINED``
system date and time is not set
``RTEMS_INVALID_ADDRESS``
``time`` is NULL
**DESCRIPTION:**
This directive obtains the system date and time in POSIX``struct timeval`` format. If the date and time
has not been set with a previous call to``rtems_clock_set``, then the``RTEMS_NOT_DEFINED`` status code is returned.
This directive obtains the system date and time in POSIX ``struct timeval``
format. If the date and time has not been set with a previous call to
``rtems_clock_set``, then the ``RTEMS_NOT_DEFINED`` status code is returned.
**NOTES:**
This directive is callable from an ISR.
This directive will not cause the running task to be
preempted. Re-initializing RTEMS causes the system date and
time to be reset to an uninitialized state. Another call to``rtems_clock_set`` is required to re-initialize the
system date and time to application specific specifications.
This directive will not cause the running task to be preempted.
Re-initializing RTEMS causes the system date and time to be reset to an
uninitialized state. Another call to ``rtems_clock_set`` is required to
re-initialize the system date and time to application specific specifications.
.. _rtems_clock_get_seconds_since_epoch:
CLOCK_GET_SECONDS_SINCE_EPOCH - Get seconds since epoch
-------------------------------------------------------
@ -386,29 +420,37 @@ CLOCK_GET_SECONDS_SINCE_EPOCH - Get seconds since epoch
.. code:: c
rtems_status_code rtems_clock_get_seconds_since_epoch(
rtems_interval \*the_interval
rtems_interval *the_interval
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - current time obtained successfully
``RTEMS_NOT_DEFINED`` - system date and time is not set
``RTEMS_INVALID_ADDRESS`` - ``the_interval`` is NULL
``RTEMS_SUCCESSFUL``
current time obtained successfully
``RTEMS_NOT_DEFINED``
system date and time is not set
``RTEMS_INVALID_ADDRESS``
``the_interval`` is NULL
**DESCRIPTION:**
This directive returns the number of seconds since the RTEMS
epoch and the current system date and time. If the date and time
has not been set with a previous call to``rtems_clock_set``, then the``RTEMS_NOT_DEFINED`` status code is returned.
This directive returns the number of seconds since the RTEMS epoch and the
current system date and time. If the date and time has not been set with a
previous call to ``rtems_clock_set``, then the ``RTEMS_NOT_DEFINED`` status
code is returned.
**NOTES:**
This directive is callable from an ISR.
This directive will not cause the running task to be
preempted. Re-initializing RTEMS causes the system date and
time to be reset to an uninitialized state. Another call to``rtems_clock_set`` is required to re-initialize the
system date and time to application specific specifications.
This directive will not cause the running task to be preempted.
Re-initializing RTEMS causes the system date and time to be reset to an
uninitialized state. Another call to ``rtems_clock_set`` is required to
re-initialize the system date and time to application specific specifications.
.. _rtems_clock_get_ticks_per_second:
CLOCK_GET_TICKS_PER_SECOND - Get ticks per second
-------------------------------------------------
@ -428,9 +470,8 @@ NONE
**DESCRIPTION:**
This directive returns the number of clock ticks per second. This
is strictly based upon the microseconds per clock tick that the
application has configured.
This directive returns the number of clock ticks per second. This is strictly
based upon the microseconds per clock tick that the application has configured.
**NOTES:**
@ -438,6 +479,8 @@ This directive is callable from an ISR.
This directive will not cause the running task to be preempted.
.. _rtems_clock_get_ticks_since_boot:
CLOCK_GET_TICKS_SINCE_BOOT - Get current ticks counter value
------------------------------------------------------------
.. index:: obtain ticks since boot
@ -459,8 +502,9 @@ NONE
This directive returns the current tick counter value. With a 1ms clock tick,
this counter overflows after 50 days since boot. This is the historical
measure of uptime in an RTEMS system. The newer service``rtems_clock_get_uptime`` is another and potentially more
accurate way of obtaining similar information.
measure of uptime in an RTEMS system. The newer service
``rtems_clock_get_uptime`` is another and potentially more accurate way of
obtaining similar information.
**NOTES:**
@ -468,6 +512,8 @@ This directive is callable from an ISR.
This directive will not cause the running task to be preempted.
.. _rtems_clock_tick_later:
CLOCK_TICK_LATER - Get tick value in the future
-----------------------------------------------
@ -478,7 +524,7 @@ CLOCK_TICK_LATER - Get tick value in the future
.. code:: c
rtems_interval rtems_clock_tick_later(
rtems_interval delta
rtems_interval delta
);
**DESCRIPTION:**
@ -491,6 +537,8 @@ This directive is callable from an ISR.
This directive will not cause the running task to be preempted.
.. _rtems_clock_tick_later_usec:
CLOCK_TICK_LATER_USEC - Get tick value in the future in microseconds
--------------------------------------------------------------------
@ -501,7 +549,7 @@ CLOCK_TICK_LATER_USEC - Get tick value in the future in microseconds
.. code:: c
rtems_interval rtems_clock_tick_later_usec(
rtems_interval delta_in_usec
rtems_interval delta_in_usec
);
**DESCRIPTION:**
@ -514,6 +562,8 @@ This directive is callable from an ISR.
This directive will not cause the running task to be preempted.
.. _rtems_clock_tick_before:
CLOCK_TICK_BEFORE - Is tick value is before a point in time
-----------------------------------------------------------
@ -524,7 +574,7 @@ CLOCK_TICK_BEFORE - Is tick value is before a point in time
.. code:: c
rtems_interval rtems_clock_tick_before(
rtems_interval tick
rtems_interval tick
);
**DESCRIPTION:**
@ -544,15 +594,17 @@ This directive will not cause the running task to be preempted.
status busy( void )
{
rtems_interval timeout = rtems_clock_tick_later_usec( 10000 );
do {
if ( ok() ) {
return success;
}
} while ( rtems_clock_tick_before( timeout ) );
return timeout;
rtems_interval timeout = rtems_clock_tick_later_usec( 10000 );
do {
if ( ok() ) {
return success;
}
} while ( rtems_clock_tick_before( timeout ) );
return timeout;
}
.. _rtems_clock_get_uptime:
CLOCK_GET_UPTIME - Get the time since boot
------------------------------------------
.. index:: clock get uptime
@ -565,28 +617,32 @@ CLOCK_GET_UPTIME - Get the time since boot
.. code:: c
rtems_status_code rtems_clock_get_uptime(
struct timespec \*uptime
struct timespec *uptime
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - clock tick processed successfully
``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL
``RTEMS_SUCCESSFUL``
clock tick processed successfully
``RTEMS_INVALID_ADDRESS``
``time_buffer`` is NULL
**DESCRIPTION:**
This directive returns the seconds and nanoseconds since the
system was booted. If the BSP supports nanosecond clock
accuracy, the time reported will probably be different on every
call.
This directive returns the seconds and nanoseconds since the system was booted.
If the BSP supports nanosecond clock accuracy, the time reported will probably
be different on every call.
**NOTES:**
This directive may be called from an ISR.
.. _rtems_clock_get_uptime_timeval:
CLOCK_GET_UPTIME_TIMEVAL - Get the time since boot in timeval format
--------------------------------------------------------------------
.. index:: clock get uptime
.. index:: clock get uptime interval
.. index:: uptime
**CALLING SEQUENCE:**
@ -596,7 +652,7 @@ CLOCK_GET_UPTIME_TIMEVAL - Get the time since boot in timeval format
.. code:: c
void rtems_clock_get_uptime_timeval(
struct timeval \*uptime
struct timeval *uptime
);
**DIRECTIVE STATUS CODES:**
@ -605,18 +661,19 @@ NONE
**DESCRIPTION:**
This directive returns the seconds and microseconds since the
system was booted. If the BSP supports nanosecond clock
accuracy, the time reported will probably be different on every
call.
This directive returns the seconds and microseconds since the system was
booted. If the BSP supports nanosecond clock accuracy, the time reported will
probably be different on every call.
**NOTES:**
This directive may be called from an ISR.
.. _rtems_clock_get_uptime_seconds:
CLOCK_GET_UPTIME_SECONDS - Get the seconds since boot
-----------------------------------------------------
.. index:: clock get uptime
.. index:: clock get uptime seconds
.. index:: uptime
**CALLING SEQUENCE:**
@ -639,6 +696,8 @@ This directive returns the seconds since the system was booted.
This directive may be called from an ISR.
.. _rtems_clock_get_uptime_nanoseconds:
CLOCK_GET_UPTIME_NANOSECONDS - Get the nanoseconds since boot
-------------------------------------------------------------
.. index:: clock get nanoseconds uptime
@ -664,6 +723,8 @@ This directive returns the nanoseconds since the system was booted.
This directive may be called from an ISR.
.. _rtems_clock_set_nanoseconds_extension:
CLOCK_SET_NANOSECONDS_EXTENSION - Install the nanoseconds since last tick handler
---------------------------------------------------------------------------------
.. index:: clock set nanoseconds extension
@ -677,32 +738,37 @@ CLOCK_SET_NANOSECONDS_EXTENSION - Install the nanoseconds since last tick handle
.. code:: c
rtems_status_code rtems_clock_set_nanoseconds_extension(
rtems_nanoseconds_extension_routine routine
rtems_nanoseconds_extension_routine routine
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - clock tick processed successfully
``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL
``RTEMS_SUCCESSFUL``
clock tick processed successfully
``RTEMS_INVALID_ADDRESS``
``time_buffer`` is NULL
**DESCRIPTION:**
This directive is used by the Clock device driver to install the``routine`` which will be invoked by the internal RTEMS method used to
obtain a highly accurate time of day. It is usually called during
the initialization of the driver.
This directive is used by the Clock device driver to install the ``routine``
which will be invoked by the internal RTEMS method used to obtain a highly
accurate time of day. It is usually called during the initialization of the
driver.
When the ``routine`` is invoked, it will determine the number of
nanoseconds which have elapsed since the last invocation of
the ``rtems_clock_tick`` directive. It should do
this as quickly as possible with as little impact as possible
on the device used as a clock source.
When the ``routine`` is invoked, it will determine the number of nanoseconds
which have elapsed since the last invocation of the ``rtems_clock_tick``
directive. It should do this as quickly as possible with as little impact as
possible on the device used as a clock source.
**NOTES:**
This directive may be called from an ISR.
This directive is called as part of every service to obtain the
current date and time as well as timestamps.
This directive is called as part of every service to obtain the current date
and time as well as timestamps.
.. _rtems_clock_tick:
CLOCK_TICK - Announce a clock tick
----------------------------------
@ -718,29 +784,21 @@ CLOCK_TICK - Announce a clock tick
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - clock tick processed successfully
``RTEMS_SUCCESSFUL``
clock tick processed successfully
**DESCRIPTION:**
This directive announces to RTEMS that a system clock
tick has occurred. The directive is usually called from the
timer interrupt ISR of the local processor. This directive
maintains the system date and time, decrements timers for
delayed tasks, timeouts, rate monotonic periods, and implements
This directive announces to RTEMS that a system clock tick has occurred. The
directive is usually called from the timer interrupt ISR of the local
processor. This directive maintains the system date and time, decrements
timers for delayed tasks, timeouts, rate monotonic periods, and implements
timeslicing.
**NOTES:**
This directive is typically called from an ISR.
The ``microseconds_per_tick`` and ``ticks_per_timeslice``
parameters in the Configuration Table contain the number of
microseconds per tick and number of ticks per timeslice,
respectively.
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
The ``microseconds_per_tick`` and ``ticks_per_timeslice`` parameters in the
Configuration Table contain the number of microseconds per tick and number of
ticks per timeslice, respectively.

260
c_user/initialization.rst
View File

@ -1,16 +1,19 @@
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
Initialization Manager
######################
Introduction
============
The Initialization Manager is responsible for
initiating and shutting down RTEMS. Initiating RTEMS involves
creating and starting all configured initialization tasks, and
for invoking the initialization routine for each user-supplied
device driver. In a multiprocessor configuration, this manager
also initializes the interprocessor communications layer. The
directives provided by the Initialization Manager are:
The Initialization Manager is responsible for initiating and shutting down
RTEMS. Initiating RTEMS involves creating and starting all configured
initialization tasks, and for invoking the initialization routine for each
user-supplied device driver. In a multiprocessor configuration, this manager
also initializes the interprocessor communications layer. The directives
provided by the Initialization Manager are:
- ``rtems_initialize_executive`` - Initialize RTEMS
@ -23,97 +26,85 @@ Initialization Tasks
--------------------
.. index:: initialization tasks
Initialization task(s) are the mechanism by which
RTEMS transfers initial control to the user's application.
Initialization tasks differ from other application tasks in that
they are defined in the User Initialization Tasks Table and
automatically created and started by RTEMS as part of its
initialization sequence. Since the initialization tasks are
scheduled using the same algorithm as all other RTEMS tasks,
they must be configured at a priority and mode which will ensure
that they will complete execution before other application tasks
execute. Although there is no upper limit on the number of
initialization tasks, an application is required to define at
least one.
Initialization task(s) are the mechanism by which RTEMS transfers initial
control to the user's application. Initialization tasks differ from other
application tasks in that they are defined in the User Initialization Tasks
Table and automatically created and started by RTEMS as part of its
initialization sequence. Since the initialization tasks are scheduled using
the same algorithm as all other RTEMS tasks, they must be configured at a
priority and mode which will ensure that they will complete execution before
other application tasks execute. Although there is no upper limit on the
number of initialization tasks, an application is required to define at least
one.
A typical initialization task will create and start
the static set of application tasks. It may also create any
other objects used by the application. Initialization tasks
which only perform initialization should delete themselves upon
completion to free resources for other tasks. Initialization
tasks may transform themselves into a "normal" application task.
This transformation typically involves changing priority and
execution mode. RTEMS does not automatically delete the
initialization tasks.
A typical initialization task will create and start the static set of
application tasks. It may also create any other objects used by the
application. Initialization tasks which only perform initialization should
delete themselves upon completion to free resources for other tasks.
Initialization tasks may transform themselves into a "normal" application task.
This transformation typically involves changing priority and execution mode.
RTEMS does not automatically delete the initialization tasks.
System Initialization
---------------------
System Initialization begins with board reset and continues
through RTEMS initialization, initialization of all device
drivers, and eventually a context switch to the first user
task. Remember, that interrupts are disabled during
initialization and the *initialization context* is not
a task in any sense and the user should be very careful
during initialization.
System Initialization begins with board reset and continues through RTEMS
initialization, initialization of all device drivers, and eventually a context
switch to the first user task. Remember, that interrupts are disabled during
initialization and the *initialization context* is not a task in any sense and
the user should be very careful during initialization.
The BSP must ensure that the there is enough stack
space reserved for the initialization context to
successfully execute the initialization routines for
all device drivers and, in multiprocessor configurations, the
Multiprocessor Communications Interface Layer initialization
routine.
The BSP must ensure that the there is enough stack space reserved for the
initialization context to successfully execute the initialization routines for
all device drivers and, in multiprocessor configurations, the Multiprocessor
Communications Interface Layer initialization routine.
The Idle Task
-------------
The Idle Task is the lowest priority task in a system
and executes only when no other task is ready to execute. This
default implementation of this task consists of an infinite
loop. RTEMS allows the Idle Task body to be replaced by a CPU
specific implementation, a BSP specific implementation or an
application specific implementation.
The Idle Task is the lowest priority task in a system and executes only when no
other task is ready to execute. This default implementation of this task
consists of an infinite loop. RTEMS allows the Idle Task body to be replaced by
a CPU specific implementation, a BSP specific implementation or an application
specific implementation.
The Idle Task is preemptible and *WILL* be preempted when
any other task is made ready to execute. This characteristic is
critical to the overall behavior of any application.
The Idle Task is preemptible and *WILL* be preempted when any other task is
made ready to execute. This characteristic is critical to the overall behavior
of any application.
Initialization Manager Failure
------------------------------
The ``rtems_fatal_error_occurred`` directive will
be invoked from ``rtems_initialize_executive``
for any of the following reasons:
The ``rtems_fatal_error_occurred`` directive will be invoked from
``rtems_initialize_executive`` for any of the following reasons:
- If either the Configuration Table or the CPU Dependent
Information Table is not provided.
- If either the Configuration Table or the CPU Dependent Information Table is
not provided.
- If the starting address of the RTEMS RAM Workspace,
supplied by the application in the Configuration Table, is NULL
or is not aligned on a four-byte boundary.
- If the starting address of the RTEMS RAM Workspace, supplied by the
application in the Configuration Table, is NULL or is not aligned on a
four-byte boundary.
- If the size of the RTEMS RAM Workspace is not large
enough to initialize and configure the system.
- If the size of the RTEMS RAM Workspace is not large enough to initialize and
configure the system.
- If the interrupt stack size specified is too small.
- If multiprocessing is configured and the node entry in
the Multiprocessor Configuration Table is not between one and
the maximum_nodes entry.
- If multiprocessing is configured and the node entry in the Multiprocessor
Configuration Table is not between one and the maximum_nodes entry.
- If a multiprocessor system is being configured and no
Multiprocessor Communications Interface is specified.
- If a multiprocessor system is being configured and no Multiprocessor
Communications Interface is specified.
- If no user initialization tasks are configured. At
least one initialization task must be configured to allow RTEMS
to pass control to the application at the end of the executive
initialization sequence.
- If no user initialization tasks are configured. At least one initialization
task must be configured to allow RTEMS to pass control to the application at
the end of the executive initialization sequence.
- If any of the user initialization tasks cannot be
created or started successfully.
- If any of the user initialization tasks cannot be created or started
successfully.
A discussion of RTEMS actions when a fatal error occurs
may be found `Announcing a Fatal Error`_.
A discussion of RTEMS actions when a fatal error occurs may be found
`Announcing a Fatal Error`_.
Operations
==========
@ -121,10 +112,10 @@ Operations
Initializing RTEMS
------------------
The Initialization Manager ``rtems_initialize_executive``
directives is called by the ``boot_card`` routine. The ``boot_card``
routine is invoked by the Board Support Package once a basic C run-time
environment is set up. This consists of
The Initialization Manager ``rtems_initialize_executive`` directives is called
by the ``boot_card`` routine. The ``boot_card`` routine is invoked by the
Board Support Package once a basic C run-time environment is set up. This
consists of
- a valid and accessible text section, read-only data, read-write data and
zero-initialized data,
@ -136,85 +127,83 @@ environment is set up. This consists of
- disabled interrupts.
The ``rtems_initialize_executive`` directive uses a system
initialization linker set to initialize only those parts of the overall RTEMS
feature set that is necessary for a particular application. See `Linker Sets`_.
Each RTEMS feature used the application may optionally register an
initialization handler. The system initialization API is available via``#included <rtems/sysinit.h>``.
The ``rtems_initialize_executive`` directive uses a system initialization
linker set to initialize only those parts of the overall RTEMS feature set that
is necessary for a particular application. See `Linker Sets`_. Each RTEMS
feature used the application may optionally register an initialization handler.
The system initialization API is available via``#included <rtems/sysinit.h>``.
A list of all initialization steps follows. Some steps are optional depending
on the requested feature set of the application. The initialization steps are
execute in the order presented here.
:dfn:`RTEMS_SYSINIT_BSP_WORK_AREAS`
`RTEMS_SYSINIT_BSP_WORK_AREAS`
The work areas consisting of C Program Heap and the RTEMS Workspace are
initialized by the Board Support Package. This step is mandatory.
:dfn:`RTEMS_SYSINIT_BSP_START`
Basic initialization step provided by the Board Support Package. This step is
mandatory.
`RTEMS_SYSINIT_BSP_START`
Basic initialization step provided by the Board Support Package. This step
is mandatory.
:dfn:`RTEMS_SYSINIT_DATA_STRUCTURES`
This directive is called when the Board Support Package has completed its basic
initialization and allows RTEMS to initialize the application environment based
upon the information in the Configuration Table, User Initialization Tasks
Table, Device Driver Table, User Extension Table, Multiprocessor Configuration
Table, and the Multiprocessor Communications Interface (MPCI) Table.
`RTEMS_SYSINIT_DATA_STRUCTURES`
This directive is called when the Board Support Package has completed its
basic initialization and allows RTEMS to initialize the application
environment based upon the information in the Configuration Table, User
Initialization Tasks Table, Device Driver Table, User Extension Table,
Multiprocessor Configuration Table, and the Multiprocessor Communications
Interface (MPCI) Table.
:dfn:`RTEMS_SYSINIT_BSP_LIBC`
Depending on the application configuration the IO library and root filesystem
is initialized. This step is mandatory.
`RTEMS_SYSINIT_BSP_LIBC`
Depending on the application configuration the IO library and root
filesystem is initialized. This step is mandatory.
:dfn:`RTEMS_SYSINIT_BEFORE_DRIVERS`
This directive performs initialization that must occur between basis RTEMS data
structure initialization and device driver initialization. In particular, in a
multiprocessor configuration, this directive will create the MPCI Server Task.
`RTEMS_SYSINIT_BEFORE_DRIVERS`
This directive performs initialization that must occur between basis RTEMS
data structure initialization and device driver initialization. In
particular, in a multiprocessor configuration, this directive will create
the MPCI Server Task.
:dfn:`RTEMS_SYSINIT_BSP_PRE_DRIVERS`
`RTEMS_SYSINIT_BSP_PRE_DRIVERS`
Initialization step performed right before device drivers are initialized
provided by the Board Support Package. This step is mandatory.
:dfn:`RTEMS_SYSINIT_DEVICE_DRIVERS`
This step initializes all statically configured device drivers and performs all
RTEMS initialization which requires device drivers to be initialized. This
step is mandatory.
In a multiprocessor configuration, this service will initialize the
Multiprocessor Communications Interface (MPCI) and synchronize with the other
nodes in the system.
`RTEMS_SYSINIT_DEVICE_DRIVERS`
This step initializes all statically configured device drivers and performs
all RTEMS initialization which requires device drivers to be initialized.
This step is mandatory. In a multiprocessor configuration, this service
will initialize the Multiprocessor Communications Interface (MPCI) and
synchronize with the other nodes in the system.
:dfn:`RTEMS_SYSINIT_BSP_POST_DRIVERS`
`RTEMS_SYSINIT_BSP_POST_DRIVERS`
Initialization step performed right after device drivers are initialized
provided by the Board Support Package. This step is mandatory.
The final action of the ``rtems_initialize_executive`` directive
is to start multitasking. RTEMS does not return to the initialization context
and the initialization stack may be re-used for interrupt processing.
The final action of the ``rtems_initialize_executive`` directive is to start
multitasking. RTEMS does not return to the initialization context and the
initialization stack may be re-used for interrupt processing.
Many of RTEMS actions during initialization are based upon
the contents of the Configuration Table. For more information
regarding the format and contents of this table, please refer
to the chapter `Configuring a System`_.
Many of RTEMS actions during initialization are based upon the contents of the
Configuration Table. For more information regarding the format and contents of
this table, please refer to the chapter `Configuring a System`_.
The final action in the initialization sequence is the
initiation of multitasking. When the scheduler and dispatcher
are enabled, the highest priority, ready task will be dispatched
to run. Control will not be returned to the Board Support
Package after multitasking is enabled. The initialization stack may be re-used
for interrupt processing.
The final action in the initialization sequence is the initiation of
multitasking. When the scheduler and dispatcher are enabled, the highest
priority, ready task will be dispatched to run. Control will not be returned
to the Board Support Package after multitasking is enabled. The initialization
stack may be re-used for interrupt processing.
Shutting Down RTEMS
-------------------
The ``rtems_shutdown_executive`` directive is invoked by the
application to end multitasking and terminate the system.
The ``rtems_shutdown_executive`` directive is invoked by the application to end
multitasking and terminate the system.
Directives
==========
This section details the Initialization Manager's
directives. A subsection is dedicated to each of this manager's
directives and describes the calling sequence, related
constants, usage, and status codes.
This section details the Initialization Manager's directives. A subsection is
dedicated to each of this manager's directives and describes the calling
sequence, related constants, usage, and status codes.
INITIALIZE_EXECUTIVE - Initialize RTEMS
---------------------------------------
@ -256,7 +245,7 @@ SHUTDOWN_EXECUTIVE - Shutdown RTEMS
.. code:: c
void rtems_shutdown_executive(
uint32_t result
uint32_t result
);
**DIRECTIVE STATUS CODES:**
@ -266,19 +255,12 @@ NONE
**DESCRIPTION:**
This directive is called when the application wishes to shutdown RTEMS. The
system is terminated with a fatal source of ``RTEMS_FATAL_SOURCE_EXIT`` and
the specified ``result`` code.
system is terminated with a fatal source of ``RTEMS_FATAL_SOURCE_EXIT`` and the
specified ``result`` code.
**NOTES:**
This directive *must* be the last RTEMS directive
invoked by an application and it *does not return* to the caller.
This directive *must* be the last RTEMS directive invoked by an application and
it *does not return* to the caller.
This directive may be called any time.
.. COMMENT: COPYRIGHT (c) 1988-2014.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.

396
c_user/interrupt_manager.rst
View File

@ -1,41 +1,43 @@
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
Interrupt Manager
#################
Introduction
============
Any real-time executive must provide a mechanism for
quick response to externally generated interrupts to satisfy the
critical time constraints of the application. The interrupt
manager provides this mechanism for RTEMS. This manager permits
quick interrupt response times by providing the critical ability
to alter task execution which allows a task to be preempted upon
exit from an ISR. The interrupt manager includes the following
directive:
Any real-time executive must provide a mechanism for quick response to
externally generated interrupts to satisfy the critical time constraints of the
application. The interrupt manager provides this mechanism for RTEMS. This
manager permits quick interrupt response times by providing the critical
ability to alter task execution which allows a task to be preempted upon exit
from an ISR. The interrupt manager includes the following directive:
- ``rtems_interrupt_catch`` - Establish an ISR
- rtems_interrupt_catch_ - Establish an ISR
- ``rtems_interrupt_disable`` - Disable Interrupts
- rtems_interrupt_disable_ - Disable Interrupts
- ``rtems_interrupt_enable`` - Enable Interrupts
- rtems_interrupt_enable_ - Enable Interrupts
- ``rtems_interrupt_flash`` - Flash Interrupt
- rtems_interrupt_flash_ - Flash Interrupt
- ``rtems_interrupt_local_disable`` - Disable Interrupts on Current Processor
- rtems_interrupt_local_disable_ - Disable Interrupts on Current Processor
- ``rtems_interrupt_local_enable`` - Enable Interrupts on Current Processor
- rtems_interrupt_local_enable_ - Enable Interrupts on Current Processor
- ``rtems_interrupt_lock_initialize`` - Initialize an ISR Lock
- rtems_interrupt_lock_initialize_ - Initialize an ISR Lock
- ``rtems_interrupt_lock_acquire`` - Acquire an ISR Lock
- rtems_interrupt_lock_acquire_ - Acquire an ISR Lock
- ``rtems_interrupt_lock_release`` - Release an ISR Lock
- rtems_interrupt_lock_release_ - Release an ISR Lock
- ``rtems_interrupt_lock_acquire_isr`` - Acquire an ISR Lock from ISR
- rtems_interrupt_lock_acquire_isr_ - Acquire an ISR Lock from ISR
- ``rtems_interrupt_lock_release_isr`` - Release an ISR Lock from ISR
- rtems_interrupt_lock_release_isr_ - Release an ISR Lock from ISR
- ``rtems_interrupt_is_in_progress`` - Is an ISR in Progress
- rtems_interrupt_is_in_progress_ - Is an ISR in Progress
Background
==========
@ -44,108 +46,98 @@ Processing an Interrupt
-----------------------
.. index:: interrupt processing
The interrupt manager allows the application to
connect a function to a hardware interrupt vector. When an
interrupt occurs, the processor will automatically vector to
RTEMS. RTEMS saves and restores all registers which are not
preserved by the normal C calling convention
for the target
processor and invokes the user's ISR. The user's ISR is
responsible for processing the interrupt, clearing the interrupt
if necessary, and device specific manipulation... index:: rtems_vector_number
The interrupt manager allows the application to connect a function to a
hardware interrupt vector. When an interrupt occurs, the processor will
automatically vector to RTEMS. RTEMS saves and restores all registers which
are not preserved by the normal C calling convention for the target processor
and invokes the user's ISR. The user's ISR is responsible for processing the
interrupt, clearing the interrupt if necessary, and device specific
manipulation.
The ``rtems_interrupt_catch``
directive connects a procedure to
an interrupt vector. The vector number is managed using
the ``rtems_vector_number`` data type.
.. index:: rtems_vector_number
The interrupt service routine is assumed
to abide by these conventions and have a prototype similar to
the following:.. index:: rtems_isr
The ``rtems_interrupt_catch`` directive connects a procedure to an interrupt
vector. The vector number is managed using the ``rtems_vector_number`` data
type.
The interrupt service routine is assumed to abide by these conventions and have
a prototype similar to the following:
.. index:: rtems_isr
.. code:: c
rtems_isr user_isr(
rtems_vector_number vector
rtems_vector_number vector
);
The vector number argument is provided by RTEMS to
allow the application to identify the interrupt source. This
could be used to allow a single routine to service interrupts
from multiple instances of the same device. For example, a
single routine could service interrupts from multiple serial
ports and use the vector number to identify which port requires
servicing.
The vector number argument is provided by RTEMS to allow the application to
identify the interrupt source. This could be used to allow a single routine to
service interrupts from multiple instances of the same device. For example, a
single routine could service interrupts from multiple serial ports and use the
vector number to identify which port requires servicing.
To minimize the masking of lower or equal priority
level interrupts, the ISR should perform the minimum actions
required to service the interrupt. Other non-essential actions
should be handled by application tasks. Once the user's ISR has
completed, it returns control to the RTEMS interrupt manager
which will perform task dispatching and restore the registers
saved before the ISR was invoked.
To minimize the masking of lower or equal priority level interrupts, the ISR
should perform the minimum actions required to service the interrupt. Other
non-essential actions should be handled by application tasks. Once the user's
ISR has completed, it returns control to the RTEMS interrupt manager which will
perform task dispatching and restore the registers saved before the ISR was
invoked.
The RTEMS interrupt manager guarantees that proper
task scheduling and dispatching are performed at the conclusion
of an ISR. A system call made by the ISR may have readied a
task of higher priority than the interrupted task. Therefore,
when the ISR completes, the postponed dispatch processing must
be performed. No dispatch processing is performed as part of
directives which have been invoked by an ISR.
The RTEMS interrupt manager guarantees that proper task scheduling and
dispatching are performed at the conclusion of an ISR. A system call made by
the ISR may have readied a task of higher priority than the interrupted task.
Therefore, when the ISR completes, the postponed dispatch processing must be
performed. No dispatch processing is performed as part of directives which
have been invoked by an ISR.
Applications must adhere to the following rule if
proper task scheduling and dispatching is to be performed:
Applications must adhere to the following rule if proper task scheduling and
dispatching is to be performed:
- ** *The interrupt manager must be used for all ISRs which
may be interrupted by the highest priority ISR which invokes an
RTEMS directive.*
.. note::
Consider a processor which allows a numerically low
interrupt level to interrupt a numerically greater interrupt
level. In this example, if an RTEMS directive is used in a
level 4 ISR, then all ISRs which execute at levels 0 through 4
must use the interrupt manager.
The interrupt manager must be used for all ISRs which may be interrupted by
the highest priority ISR which invokes an RTEMS directive.
Interrupts are nested whenever an interrupt occurs
during the execution of another ISR. RTEMS supports efficient
interrupt nesting by allowing the nested ISRs to terminate
without performing any dispatch processing. Only when the
Consider a processor which allows a numerically low interrupt level to
interrupt a numerically greater interrupt level. In this example, if an RTEMS
directive is used in a level 4 ISR, then all ISRs which execute at levels 0
through 4 must use the interrupt manager.
Interrupts are nested whenever an interrupt occurs during the execution of
another ISR. RTEMS supports efficient interrupt nesting by allowing the nested
ISRs to terminate without performing any dispatch processing. Only when the
outermost ISR terminates will the postponed dispatching occur.
RTEMS Interrupt Levels
----------------------
.. index:: interrupt levels
Many processors support multiple interrupt levels or
priorities. The exact number of interrupt levels is processor
dependent. RTEMS internally supports 256 interrupt levels which
are mapped to the processor's interrupt levels. For specific
information on the mapping between RTEMS and the target
processor's interrupt levels, refer to the Interrupt Processing
chapter of the Applications Supplement document for a specific
target processor.
Many processors support multiple interrupt levels or priorities. The exact
number of interrupt levels is processor dependent. RTEMS internally supports
256 interrupt levels which are mapped to the processor's interrupt levels. For
specific information on the mapping between RTEMS and the target processor's
interrupt levels, refer to the Interrupt Processing chapter of the Applications
Supplement document for a specific target processor.
Disabling of Interrupts by RTEMS
--------------------------------
.. index:: disabling interrupts
During the execution of directive calls, critical
sections of code may be executed. When these sections are
encountered, RTEMS disables all maskable interrupts before the
execution of the section and restores them to the previous level
upon completion of the section. RTEMS has been optimized to
ensure that interrupts are disabled for a minimum length of
time. The maximum length of time interrupts are disabled by
RTEMS is processor dependent and is detailed in the Timing
Specification chapter of the Applications Supplement document
for a specific target processor.
During the execution of directive calls, critical sections of code may be
executed. When these sections are encountered, RTEMS disables all maskable
interrupts before the execution of the section and restores them to the
previous level upon completion of the section. RTEMS has been optimized to
ensure that interrupts are disabled for a minimum length of time. The maximum
length of time interrupts are disabled by RTEMS is processor dependent and is
detailed in the Timing Specification chapter of the Applications Supplement
document for a specific target processor.
Non-maskable interrupts (NMI) cannot be disabled, and
ISRs which execute at this level MUST NEVER issue RTEMS system
calls. If a directive is invoked, unpredictable results may
occur due to the inability of RTEMS to protect its critical
sections. However, ISRs that make no system calls may safely
execute as non-maskable interrupts.
Non-maskable interrupts (NMI) cannot be disabled, and ISRs which execute at
this level MUST NEVER issue RTEMS system calls. If a directive is invoked,
unpredictable results may occur due to the inability of RTEMS to protect its
critical sections. However, ISRs that make no system calls may safely execute
as non-maskable interrupts.
Operations
==========
@ -153,32 +145,28 @@ Operations
Establishing an ISR
-------------------
The ``rtems_interrupt_catch``
directive establishes an ISR for
the system. The address of the ISR and its associated CPU
vector number are specified to this directive. This directive
installs the RTEMS interrupt wrapper in the processor's
Interrupt Vector Table and the address of the user's ISR in the
RTEMS' Vector Table. This directive returns the previous
contents of the specified vector in the RTEMS' Vector Table.
The ``rtems_interrupt_catch`` directive establishes an ISR for the system. The
address of the ISR and its associated CPU vector number are specified to this
directive. This directive installs the RTEMS interrupt wrapper in the
processor's Interrupt Vector Table and the address of the user's ISR in the
RTEMS' Vector Table. This directive returns the previous contents of the
specified vector in the RTEMS' Vector Table.
Directives Allowed from an ISR
------------------------------
Using the interrupt manager ensures that RTEMS knows
when a directive is being called from an ISR. The ISR may then
use system calls to synchronize itself with an application task.
The synchronization may involve messages, events or signals
being passed by the ISR to the desired task. Directives invoked
by an ISR must operate only on objects which reside on the local
node. The following is a list of RTEMS system calls that may be
made from an ISR:
Using the interrupt manager ensures that RTEMS knows when a directive is being
called from an ISR. The ISR may then use system calls to synchronize itself
with an application task. The synchronization may involve messages, events or
signals being passed by the ISR to the desired task. Directives invoked by an
ISR must operate only on objects which reside on the local node. The following
is a list of RTEMS system calls that may be made from an ISR:
- Task Management
Although it is acceptable to operate on the RTEMS_SELF task (e.g.
the currently executing task), while in an ISR, this will refer
to the interrupted task. Most of the time, it is an application
implementation error to use RTEMS_SELF from an ISR.
Although it is acceptable to operate on the RTEMS_SELF task (e.g. the
currently executing task), while in an ISR, this will refer to the
interrupted task. Most of the time, it is an application implementation
error to use RTEMS_SELF from an ISR.
- rtems_task_suspend
- rtems_task_resume
@ -253,10 +241,11 @@ made from an ISR:
Directives
==========
This section details the interrupt manager's
directives. A subsection is dedicated to each of this manager's
directives and describes the calling sequence, related
constants, usage, and status codes.
This section details the interrupt manager's directives. A subsection is
dedicated to each of this manager's directives and describes the calling
sequence, related constants, usage, and status codes.
.. _rtems_interrupt_catch:
INTERRUPT_CATCH - Establish an ISR
----------------------------------
@ -270,31 +259,38 @@ INTERRUPT_CATCH - Establish an ISR
.. code:: c
rtems_status_code rtems_interrupt_catch(
rtems_isr_entry new_isr_handler,
rtems_vector_number vector,
rtems_isr_entry \*old_isr_handler
rtems_isr_entry new_isr_handler,
rtems_vector_number vector,
rtems_isr_entry *old_isr_handler
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - ISR established successfully
``RTEMS_INVALID_NUMBER`` - illegal vector number
``RTEMS_INVALID_ADDRESS`` - illegal ISR entry point or invalid ``old_isr_handler``
``RTEMS_SUCCESSFUL``
ISR established successfully
``RTEMS_INVALID_NUMBER``
illegal vector number
``RTEMS_INVALID_ADDRESS``
illegal ISR entry point or invalid ``old_isr_handler``
**DESCRIPTION:**
This directive establishes an interrupt service
routine (ISR) for the specified interrupt vector number. The``new_isr_handler`` parameter specifies the entry point of the ISR.
The entry point of the previous ISR for the specified vector is
returned in ``old_isr_handler``.
This directive establishes an interrupt service routine (ISR) for the specified
interrupt vector number. The ``new_isr_handler`` parameter specifies the entry
point of the ISR. The entry point of the previous ISR for the specified vector
is returned in ``old_isr_handler``.
To release an interrupt vector, pass the old handler's address obtained
when the vector was first capture.
To release an interrupt vector, pass the old handler's address obtained when
the vector was first capture.
**NOTES:**
This directive will not cause the calling task to be preempted.
.. _rtems_interrupt_disable:
INTERRUPT_DISABLE - Disable Interrupts
--------------------------------------
.. index:: disable interrupts
@ -306,9 +302,8 @@ INTERRUPT_DISABLE - Disable Interrupts
.. code:: c
void rtems_interrupt_disable(
rtems_interrupt_level level
rtems_interrupt_level level
);
/* this is implemented as a macro and sets level as a side-effect \*/
**DIRECTIVE STATUS CODES:**
@ -316,20 +311,23 @@ NONE
**DESCRIPTION:**
This directive disables all maskable interrupts and returns
the previous ``level``. A later invocation of the``rtems_interrupt_enable`` directive should be used to
restore the interrupt level.
.. sidebar:: *Macro*
This directive is implemented as a macro which modifies the ``level``
parameter.
This directive disables all maskable interrupts and returns the previous
``level``. A later invocation of the ``rtems_interrupt_enable`` directive
should be used to restore the interrupt level.
**NOTES:**
This directive will not cause the calling task to be preempted.
*This directive is implemented as a macro which modifies the ``level``
parameter.*
This directive is only available on uni-processor configurations. The
directive ``rtems_interrupt_local_disable`` is available on all
configurations.
directive ``rtems_interrupt_local_disable`` is available on all configurations.
.. _rtems_interrupt_enable:
INTERRUPT_ENABLE - Enable Interrupts
------------------------------------
@ -342,7 +340,7 @@ INTERRUPT_ENABLE - Enable Interrupts
.. code:: c
void rtems_interrupt_enable(
rtems_interrupt_level level
rtems_interrupt_level level
);
**DIRECTIVE STATUS CODES:**
@ -351,19 +349,20 @@ NONE
**DESCRIPTION:**
This directive enables maskable interrupts to the ``level``
which was returned by a previous call to``rtems_interrupt_disable``.
Immediately prior to invoking this directive, maskable interrupts should
be disabled by a call to ``rtems_interrupt_disable``
and will be enabled when this directive returns to the caller.
This directive enables maskable interrupts to the ``level`` which was returned
by a previous call to ``rtems_interrupt_disable``. Immediately prior to
invoking this directive, maskable interrupts should be disabled by a call to
``rtems_interrupt_disable`` and will be enabled when this directive returns to
the caller.
**NOTES:**
This directive will not cause the calling task to be preempted.
This directive is only available on uni-processor configurations. The
directive ``rtems_interrupt_local_enable`` is available on all
configurations.
directive ``rtems_interrupt_local_enable`` is available on all configurations.
.. _rtems_interrupt_flash:
INTERRUPT_FLASH - Flash Interrupts
----------------------------------
@ -376,7 +375,7 @@ INTERRUPT_FLASH - Flash Interrupts
.. code:: c
void rtems_interrupt_flash(
rtems_interrupt_level level
rtems_interrupt_level level
);
**DIRECTIVE STATUS CODES:**
@ -385,19 +384,21 @@ NONE
**DESCRIPTION:**
This directive temporarily enables maskable interrupts to the ``level``
which was returned by a previous call to``rtems_interrupt_disable``.
Immediately prior to invoking this directive, maskable interrupts should
be disabled by a call to ``rtems_interrupt_disable``
and will be redisabled when this directive returns to the caller.
This directive temporarily enables maskable interrupts to the ``level`` which
was returned by a previous call to ``rtems_interrupt_disable``. Immediately
prior to invoking this directive, maskable interrupts should be disabled by a
call to ``rtems_interrupt_disable`` and will be redisabled when this directive
returns to the caller.
**NOTES:**
This directive will not cause the calling task to be preempted.
This directive is only available on uni-processor configurations. The
directives ``rtems_interrupt_local_disable`` and``rtems_interrupt_local_enable`` is available on all
configurations.
directives ``rtems_interrupt_local_disable``
and``rtems_interrupt_local_enable`` is available on all configurations.
.. _rtems_interrupt_local_disable:
INTERRUPT_LOCAL_DISABLE - Disable Interrupts on Current Processor
-----------------------------------------------------------------
@ -410,9 +411,8 @@ INTERRUPT_LOCAL_DISABLE - Disable Interrupts on Current Processor
.. code:: c
void rtems_interrupt_local_disable(
rtems_interrupt_level level
rtems_interrupt_level level
);
/* this is implemented as a macro and sets level as a side-effect \*/
**DIRECTIVE STATUS CODES:**
@ -420,20 +420,24 @@ NONE
**DESCRIPTION:**
This directive disables all maskable interrupts and returns
the previous ``level``. A later invocation of the``rtems_interrupt_local_enable`` directive should be used to
restore the interrupt level.
.. sidebar:: *Macro*
This directive is implemented as a macro which modifies the ``level``
parameter.
This directive disables all maskable interrupts and returns the previous
``level``. A later invocation of the ``rtems_interrupt_local_enable`` directive
should be used to restore the interrupt level.
**NOTES:**
This directive will not cause the calling task to be preempted.
*This directive is implemented as a macro which modifies the ``level``
parameter.*
On SMP configurations this will not ensure system wide mutual exclusion. Use
interrupt locks instead.
.. _rtems_interrupt_local_enable:
INTERRUPT_LOCAL_ENABLE - Enable Interrupts on Current Processor
---------------------------------------------------------------
.. index:: enable interrupts
@ -445,7 +449,7 @@ INTERRUPT_LOCAL_ENABLE - Enable Interrupts on Current Processor
.. code:: c
void rtems_interrupt_local_enable(
rtems_interrupt_level level
rtems_interrupt_level level
);
**DIRECTIVE STATUS CODES:**
@ -454,16 +458,18 @@ NONE
**DESCRIPTION:**
This directive enables maskable interrupts to the ``level``
which was returned by a previous call to``rtems_interrupt_local_disable``.
Immediately prior to invoking this directive, maskable interrupts should
be disabled by a call to ``rtems_interrupt_local_disable``
and will be enabled when this directive returns to the caller.
This directive enables maskable interrupts to the ``level`` which was returned
by a previous call to ``rtems_interrupt_local_disable``. Immediately prior to
invoking this directive, maskable interrupts should be disabled by a call to
``rtems_interrupt_local_disable`` and will be enabled when this directive
returns to the caller.
**NOTES:**
This directive will not cause the calling task to be preempted.
.. _rtems_interrupt_lock_initialize:
INTERRUPT_LOCK_INITIALIZE - Initialize an ISR Lock
--------------------------------------------------
@ -474,7 +480,7 @@ INTERRUPT_LOCK_INITIALIZE - Initialize an ISR Lock
.. code:: c
void rtems_interrupt_lock_initialize(
rtems_interrupt_lock \*lock
rtems_interrupt_lock *lock
);
**DIRECTIVE STATUS CODES:**
@ -489,6 +495,8 @@ Initializes an interrupt lock.
Concurrent initialization leads to unpredictable results.
.. _rtems_interrupt_lock_acquire:
INTERRUPT_LOCK_ACQUIRE - Acquire an ISR Lock
--------------------------------------------
@ -499,8 +507,8 @@ INTERRUPT_LOCK_ACQUIRE - Acquire an ISR Lock
.. code:: c
void rtems_interrupt_lock_acquire(
rtems_interrupt_lock \*lock,
rtems_interrupt_level level
rtems_interrupt_lock *lock,
rtems_interrupt_level level
);
**DIRECTIVE STATUS CODES:**
@ -517,6 +525,8 @@ SMP lock.
This directive will not cause the calling thread to be preempted. This
directive can be used in thread and interrupt context.
.. _rtems_interrupt_lock_release:
INTERRUPT_LOCK_RELEASE - Release an ISR Lock
--------------------------------------------
@ -527,8 +537,8 @@ INTERRUPT_LOCK_RELEASE - Release an ISR Lock
.. code:: c
void rtems_interrupt_lock_release(
rtems_interrupt_lock \*lock,
rtems_interrupt_level level
rtems_interrupt_lock *lock,
rtems_interrupt_level level
);
**DIRECTIVE STATUS CODES:**
@ -545,6 +555,8 @@ releases a SMP lock.
This directive will not cause the calling thread to be preempted. This
directive can be used in thread and interrupt context.
.. _rtems_interrupt_lock_acquire_isr:
INTERRUPT_LOCK_ACQUIRE_ISR - Acquire an ISR Lock from ISR
---------------------------------------------------------
@ -555,8 +567,8 @@ INTERRUPT_LOCK_ACQUIRE_ISR - Acquire an ISR Lock from ISR
.. code:: c
void rtems_interrupt_lock_acquire_isr(
rtems_interrupt_lock \*lock,
rtems_interrupt_level level
rtems_interrupt_lock *lock,
rtems_interrupt_level level
);
**DIRECTIVE STATUS CODES:**
@ -577,6 +589,8 @@ protected by this lock, then the result is unpredictable.
This directive should be called from the corresponding interrupt service
routine.
.. _rtems_interrupt_lock_release_isr:
INTERRUPT_LOCK_RELEASE_ISR - Release an ISR Lock from ISR
---------------------------------------------------------
@ -587,8 +601,8 @@ INTERRUPT_LOCK_RELEASE_ISR - Release an ISR Lock from ISR
.. code:: c
void rtems_interrupt_lock_release_isr(
rtems_interrupt_lock \*lock,
rtems_interrupt_level level
rtems_interrupt_lock *lock,
rtems_interrupt_level level
);
**DIRECTIVE STATUS CODES:**
@ -605,6 +619,8 @@ directive releases a SMP lock.
This directive should be called from the corresponding interrupt service
routine.
.. _rtems_interrupt_is_in_progress:
INTERRUPT_IS_IN_PROGRESS - Is an ISR in Progress
------------------------------------------------
.. index:: is interrupt in progress
@ -615,7 +631,7 @@ INTERRUPT_IS_IN_PROGRESS - Is an ISR in Progress
.. code:: c
bool rtems_interrupt_is_in_progress( void );
bool rtems_interrupt_is_in_progress(void);
**DIRECTIVE STATUS CODES:**
@ -623,19 +639,11 @@ NONE
**DESCRIPTION:**
This directive returns ``TRUE`` if the processor is currently
servicing an interrupt and ``FALSE`` otherwise. A return value
of ``TRUE`` indicates that the caller is an interrupt service
routine, *NOT* a task. The directives available to an interrupt
service routine are restricted.
This directive returns ``TRUE`` if the processor is currently servicing an
interrupt and ``FALSE`` otherwise. A return value of ``TRUE`` indicates that
the caller is an interrupt service routine, *NOT* a task. The directives
available to an interrupt service routine are restricted.
**NOTES:**
This directive will not cause the calling task to be preempted.
.. COMMENT: COPYRIGHT (c) 1988-2008
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.

355
c_user/key_concepts.rst
View File

@ -1,106 +1,108 @@
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
Key Concepts
############
Introduction
============
The facilities provided by RTEMS are built upon a
foundation of very powerful concepts. These concepts must be
understood before the application developer can efficiently
utilize RTEMS. The purpose of this chapter is to familiarize
The facilities provided by RTEMS are built upon a foundation of very powerful
concepts. These concepts must be understood before the application developer
can efficiently utilize RTEMS. The purpose of this chapter is to familiarize
one with these concepts.
.. _objects:
Objects
=======
.. index:: objects
RTEMS provides directives which can be used to
dynamically create, delete, and manipulate a set of predefined
object types. These types include tasks, message queues,
semaphores, memory regions, memory partitions, timers, ports,
and rate monotonic periods. The object-oriented nature of RTEMS
encourages the creation of modular applications built upon
re-usable "building block" routines.
RTEMS provides directives which can be used to dynamically create, delete, and
manipulate a set of predefined object types. These types include tasks,
message queues, semaphores, memory regions, memory partitions, timers, ports,
and rate monotonic periods. The object-oriented nature of RTEMS encourages the
creation of modular applications built upon re-usable "building block"
routines.
All objects are created on the local node as required
by the application and have an RTEMS assigned ID. All objects
have a user-assigned name. Although a relationship exists
between an object's name and its RTEMS assigned ID, the name and
ID are not identical. Object names are completely arbitrary and
selected by the user as a meaningful "tag" which may commonly
reflect the object's use in the application. Conversely, object
IDs are designed to facilitate efficient object manipulation by
the executive.
All objects are created on the local node as required by the application and
have an RTEMS assigned ID. All objects have a user-assigned name. Although a
relationship exists between an object's name and its RTEMS assigned ID, the
name and ID are not identical. Object names are completely arbitrary and
selected by the user as a meaningful "tag" which may commonly reflect the
object's use in the application. Conversely, object IDs are designed to
facilitate efficient object manipulation by the executive.
Object Names
------------
.. index:: object name
.. index:: rtems_object_name
An object name is an unsigned thirty-two bit entity
associated with the object by the user. The data type``rtems_name`` is used to store object names... index:: rtems_build_name
An object name is an unsigned thirty-two bit entity associated with the object
by the user. The data type ``rtems_name`` is used to store object
names... index:: rtems_build_name
Although not required by RTEMS, object names are often composed of four ASCII
characters which help identify that object. For example, a task which causes a
light to blink might be called "LITE". The ``rtems_build_name`` routine is
provided to build an object name from four ASCII characters. The following
example illustrates this: .. code:: c
Although not required by RTEMS, object names are often
composed of four ASCII characters which help identify that object.
For example, a task which causes a light to blink might be
called "LITE". The ``rtems_build_name`` routine
is provided to build an object name from four ASCII characters.
The following example illustrates this:
.. code:: c
rtems_object_name my_name;
my_name = rtems_build_name( 'L', 'I', 'T', 'E' );
However, it is not required that the application use ASCII
characters to build object names. For example, if an
application requires one-hundred tasks, it would be difficult to
assign meaningful ASCII names to each task. A more convenient
approach would be to name them the binary values one through
However, it is not required that the application use ASCII characters to build
object names. For example, if an application requires one-hundred tasks, it
would be difficult to assign meaningful ASCII names to each task. A more
convenient approach would be to name them the binary values one through
one-hundred, respectively... index:: rtems_object_get_name
RTEMS provides a helper routine, ``rtems_object_get_name``,
which can be used to obtain the name of any RTEMS object using just
its ID. This routine attempts to convert the name into a printable string.
RTEMS provides a helper routine, ``rtems_object_get_name``, which can be used
to obtain the name of any RTEMS object using just its ID. This routine
attempts to convert the name into a printable string.
The following example illustrates the use of this method to print an object
name:
The following example illustrates the use of this method to print
an object name:
.. code:: c
#include <rtems.h>
#include <rtems/bspIo.h>
void print_name(rtems_id id)
{
char buffer[10]; /* name assumed to be 10 characters or less \*/
char \*result;
result = rtems_object_get_name( id, sizeof(buffer), buffer );
printk( "ID=0x%08x name=%s\\n", id, ((result) ? result : "no name") );
char buffer[10]; /* name assumed to be 10 characters or less */
char *result;
result = rtems_object_get_name( id, sizeof(buffer), buffer );
printk( "ID=0x%08x name=%s\n", id, ((result) ? result : "no name") );
}
Object IDs
----------
.. index:: object ID
.. index:: object ID composition
.. index:: rtems_id
An object ID is a unique unsigned integer value which uniquely identifies
an object instance. Object IDs are passed as arguments to many directives
in RTEMS and RTEMS translates the ID to an internal object pointer. The
efficient manipulation of object IDs is critical to the performance
of RTEMS services. Because of this, there are two object Id formats
defined. Each target architecture specifies which format it will use.
There is a thirty-two bit format which is used for most of the supported
architectures and supports multiprocessor configurations. There is also
a simpler sixteen bit format which is appropriate for smaller target
architectures and does not support multiprocessor configurations.
An object ID is a unique unsigned integer value which uniquely identifies an
object instance. Object IDs are passed as arguments to many directives in
RTEMS and RTEMS translates the ID to an internal object pointer. The efficient
manipulation of object IDs is critical to the performance of RTEMS services.
Because of this, there are two object Id formats defined. Each target
architecture specifies which format it will use. There is a thirty-two bit
format which is used for most of the supported architectures and supports
multiprocessor configurations. There is also a simpler sixteen bit format
which is appropriate for smaller target architectures and does not support
multiprocessor configurations.
Thirty-Two Object ID Format
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The thirty-two bit format for an object ID is composed of four parts: API,
object class, node, and index. The data type ``rtems_id``
is used to store object IDs.
object class, node, and index. The data type ``rtems_id`` is used to store
object IDs.
.. code:: c
@ -111,21 +113,19 @@ is used to store object IDs.
| | | | |
+---------+-------+--------------+-------------------------------+
The most significant five bits are the object class. The next
three bits indicate the API to which the object class belongs.
The next eight bits (16-23) are the number of the node on which
this object was created. The node number is always one (1) in a single
processor system. The least significant sixteen bits form an
identifier within a particular object type. This identifier,
called the object index, ranges in value from 1 to the maximum
The most significant five bits are the object class. The next three bits
indicate the API to which the object class belongs. The next eight bits
(16-23) are the number of the node on which this object was created. The node
number is always one (1) in a single processor system. The least significant
sixteen bits form an identifier within a particular object type. This
identifier, called the object index, ranges in value from 1 to the maximum
number of objects configured for this object type.
Sixteen Bit Object ID Format
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The sixteen bit format for an object ID is composed of three parts: API,
object class, and index. The data type ``rtems_id``
is used to store object IDs.
The sixteen bit format for an object ID is composed of three parts: API, object
class, and index. The data type ``rtems_id`` is used to store object IDs.
.. code:: c
@ -137,39 +137,35 @@ is used to store object IDs.
+---------+-------+--------------+
The sixteen-bit format is designed to be as similar as possible to the
thrity-two bit format. The differences are limited to the eliminatation
of the node field and reduction of the index field from sixteen-bits
to 8-bits. Thus the sixteen bit format only supports up to 255 object
instances per API/Class combination and single processor systems.
As this format is typically utilized by sixteen-bit processors with
limited address space, this is more than enough object instances.
thrity-two bit format. The differences are limited to the eliminatation of the
node field and reduction of the index field from sixteen-bits to 8-bits. Thus
the sixteen bit format only supports up to 255 object instances per API/Class
combination and single processor systems. As this format is typically utilized
by sixteen-bit processors with limited address space, this is more than enough
object instances.
Object ID Description
---------------------
The components of an object ID make it possible
to quickly locate any object in even the most complicated
multiprocessor system. Object ID's are associated with an
object by RTEMS when the object is created and the corresponding
ID is returned by the appropriate object create directive. The
object ID is required as input to all directives involving
objects, except those which create an object or obtain the ID of
an object.
The components of an object ID make it possible to quickly locate any object in
even the most complicated multiprocessor system. Object ID's are associated
with an object by RTEMS when the object is created and the corresponding ID is
returned by the appropriate object create directive. The object ID is required
as input to all directives involving objects, except those which create an
object or obtain the ID of an object.
The object identification directives can be used to
dynamically obtain a particular object's ID given its name.
This mapping is accomplished by searching the name table
associated with this object type. If the name is non-unique,
then the ID associated with the first occurrence of the name
will be returned to the application. Since object IDs are
returned when the object is created, the object identification
directives are not necessary in a properly designed single
processor application.
The object identification directives can be used to dynamically obtain a
particular object's ID given its name. This mapping is accomplished by
searching the name table associated with this object type. If the name is
non-unique, then the ID associated with the first occurrence of the name will
be returned to the application. Since object IDs are returned when the object
is created, the object identification directives are not necessary in a
properly designed single processor application.
In addition, services are provided to portably examine the subcomponents of an
RTEMS ID. These services are described in detail later in this manual but are
prototyped as follows:.. index:: obtaining class from object ID
In addition, services are provided to portably examine the
subcomponents of an RTEMS ID. These services are
described in detail later in this manual but are prototyped
as follows:.. index:: obtaining class from object ID
.. index:: obtaining node from object ID
.. index:: obtaining index from object ID
.. index:: get class from object ID
@ -187,26 +183,24 @@ as follows:.. index:: obtaining class from object ID
uint32_t rtems_object_id_get_node( rtems_id );
uint32_t rtems_object_id_get_index( rtems_id );
An object control block is a data structure defined
by RTEMS which contains the information necessary to manage a
particular object type. For efficiency reasons, the format of
each object type's control block is different. However, many of
the fields are similar in function. The number of each type of
control block is application dependent and determined by the
values specified in the user's Configuration Table. An object
control block is allocated at object create time and freed when
the object is deleted. With the exception of user extension
routines, object control blocks are not directly manipulated by
user applications.
An object control block is a data structure defined by RTEMS which contains the
information necessary to manage a particular object type. For efficiency
reasons, the format of each object type's control block is different. However,
many of the fields are similar in function. The number of each type of control
block is application dependent and determined by the values specified in the
user's Configuration Table. An object control block is allocated at object
create time and freed when the object is deleted. With the exception of user
extension routines, object control blocks are not directly manipulated by user
applications.
Communication and Synchronization
=================================
.. index:: communication and synchronization
In real-time multitasking applications, the ability
for cooperating execution threads to communicate and synchronize
with each other is imperative. A real-time executive should
provide an application with the following capabilities:
In real-time multitasking applications, the ability for cooperating execution
threads to communicate and synchronize with each other is imperative. A
real-time executive should provide an application with the following
capabilities:
- Data transfer between cooperating tasks
@ -216,15 +210,13 @@ provide an application with the following capabilities:
- Synchronization of tasks and ISRs
Most RTEMS managers can be used to provide some form
of communication and/or synchronization. However, managers
dedicated specifically to communication and synchronization
provide well established mechanisms which directly map to the
application's varying needs. This level of flexibility allows
the application designer to match the features of a particular
manager with the complexity of communication and synchronization
required. The following managers were specifically designed for
communication and synchronization:
Most RTEMS managers can be used to provide some form of communication and/or
synchronization. However, managers dedicated specifically to communication and
synchronization provide well established mechanisms which directly map to the
application's varying needs. This level of flexibility allows the application
designer to match the features of a particular manager with the complexity of
communication and synchronization required. The following managers were
specifically designed for communication and synchronization:
- Semaphore
@ -234,83 +226,69 @@ communication and synchronization:
- Signal
The semaphore manager supports mutual exclusion
involving the synchronization of access to one or more shared
user resources. Binary semaphores may utilize the optional
priority inheritance algorithm to avoid the problem of priority
The semaphore manager supports mutual exclusion involving the synchronization
of access to one or more shared user resources. Binary semaphores may utilize
the optional priority inheritance algorithm to avoid the problem of priority
inversion. The message manager supports both communication and
synchronization, while the event manager primarily provides a
high performance synchronization mechanism. The signal manager
supports only asynchronous communication and is typically used
for exception handling.
synchronization, while the event manager primarily provides a high performance
synchronization mechanism. The signal manager supports only asynchronous
communication and is typically used for exception handling.
Time
====
.. index:: time
The development of responsive real-time applications
requires an understanding of how RTEMS maintains and supports
time-related operations. The basic unit of time in RTEMS is
known as a tick. The frequency of clock ticks is completely
application dependent and determines the granularity and
accuracy of all interval and calendar time operations... index:: rtems_interval
The development of responsive real-time applications requires an understanding
of how RTEMS maintains and supports time-related operations. The basic unit of
time in RTEMS is known as a tick. The frequency of clock ticks is completely
application dependent and determines the granularity and accuracy of all
interval and calendar time operations... index:: rtems_interval
By tracking time in units of ticks, RTEMS is capable
of supporting interval timing functions such as task delays,
timeouts, timeslicing, the delayed execution of timer service
routines, and the rate monotonic scheduling of tasks. An
interval is defined as a number of ticks relative to the current
time. For example, when a task delays for an interval of ten
ticks, it is implied that the task will not execute until ten
clock ticks have occurred.
All intervals are specified using data type``rtems_interval``.
By tracking time in units of ticks, RTEMS is capable of supporting interval
timing functions such as task delays, timeouts, timeslicing, the delayed
execution of timer service routines, and the rate monotonic scheduling of
tasks. An interval is defined as a number of ticks relative to the current
time. For example, when a task delays for an interval of ten ticks, it is
implied that the task will not execute until ten clock ticks have occurred.
All intervals are specified using data type ``rtems_interval``.
A characteristic of interval timing is that the
actual interval period may be a fraction of a tick less than the
interval requested. This occurs because the time at which the
delay timer is set up occurs at some time between two clock
ticks. Therefore, the first countdown tick occurs in less than
the complete time interval for a tick. This can be a problem if
the clock granularity is large.
A characteristic of interval timing is that the actual interval period may be a
fraction of a tick less than the interval requested. This occurs because the
time at which the delay timer is set up occurs at some time between two clock
ticks. Therefore, the first countdown tick occurs in less than the complete
time interval for a tick. This can be a problem if the clock granularity is
large.
The rate monotonic scheduling algorithm is a hard
real-time scheduling methodology. This methodology provides
rules which allows one to guarantee that a set of independent
periodic tasks will always meet their deadlines - even under
transient overload conditions. The rate monotonic manager
provides directives built upon the Clock Manager's interval
timer support routines.
The rate monotonic scheduling algorithm is a hard real-time scheduling
methodology. This methodology provides rules which allows one to guarantee
that a set of independent periodic tasks will always meet their deadlines -
even under transient overload conditions. The rate monotonic manager provides
directives built upon the Clock Manager's interval timer support routines.
Interval timing is not sufficient for the many
applications which require that time be kept in wall time or
true calendar form. Consequently, RTEMS maintains the current
date and time. This allows selected time operations to be
scheduled at an actual calendar date and time. For example, a
task could request to delay until midnight on New Year's Eve
before lowering the ball at Times Square.
The data type ``rtems_time_of_day`` is used to specify
calendar time in RTEMS services.
See `Time and Date Data Structures`_
Interval timing is not sufficient for the many applications which require that
time be kept in wall time or true calendar form. Consequently, RTEMS maintains
the current date and time. This allows selected time operations to be
scheduled at an actual calendar date and time. For example, a task could
request to delay until midnight on New Year's Eve before lowering the ball at
Times Square. The data type ``rtems_time_of_day`` is used to specify calendar
time in RTEMS services. See `Time and Date Data Structures`_
... index:: rtems_time_of_day
Obviously, the directives which use intervals or wall
time cannot operate without some external mechanism which
provides a periodic clock tick. This clock tick is typically
provided by a real time clock or counter/timer device.
Obviously, the directives which use intervals or wall time cannot operate
without some external mechanism which provides a periodic clock tick. This
clock tick is typically provided by a real time clock or counter/timer device.
Memory Management
=================
.. index:: memory management
RTEMS memory management facilities can be grouped
into two classes: dynamic memory allocation and address
translation. Dynamic memory allocation is required by
applications whose memory requirements vary through the
application's course of execution. Address translation is
needed by applications which share memory with another CPU or an
intelligent Input/Output processor. The following RTEMS
managers provide facilities to manage memory:
RTEMS memory management facilities can be grouped into two classes: dynamic
memory allocation and address translation. Dynamic memory allocation is
required by applications whose memory requirements vary through the
application's course of execution. Address translation is needed by
applications which share memory with another CPU or an intelligent Input/Output
processor. The following RTEMS managers provide facilities to manage memory:
- Region
@ -318,21 +296,12 @@ managers provide facilities to manage memory:
- Dual Ported Memory
RTEMS memory management features allow an application
to create simple memory pools of fixed size buffers and/or more
complex memory pools of variable size segments. The partition
manager provides directives to manage and maintain pools of
fixed size entities such as resource control blocks.
Alternatively, the region manager provides a more general
purpose memory allocation scheme that supports variable size
blocks of memory which are dynamically obtained and freed by the
application. The dual-ported memory manager provides executive
support for address translation between internal and external
dual-ported RAM address space.
.. COMMENT: COPYRIGHT (c) 1988-2002.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
RTEMS memory management features allow an application to create simple memory
pools of fixed size buffers and/or more complex memory pools of variable size
segments. The partition manager provides directives to manage and maintain
pools of fixed size entities such as resource control blocks. Alternatively,
the region manager provides a more general purpose memory allocation scheme
that supports variable size blocks of memory which are dynamically obtained and
freed by the application. The dual-ported memory manager provides executive
support for address translation between internal and external dual-ported RAM
address space.

540
c_user/overview.rst
View File

@ -1,13 +1,16 @@
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
Overview
########
Introduction
============
RTEMS, Real-Time Executive for Multiprocessor Systems, is a
real-time executive (kernel) which provides a high performance
environment for embedded military applications including the
following features:
RTEMS, Real-Time Executive for Multiprocessor Systems, is a real-time executive
(kernel) which provides a high performance environment for embedded military
applications including the following features:
- multitasking capabilities
@ -27,164 +30,153 @@ following features:
- high level of user configurability
This manual describes the usage of RTEMS for
applications written in the C programming language. Those
implementation details that are processor dependent are provided
in the Applications Supplement documents. A supplement
document which addresses specific architectural issues that
affect RTEMS is provided for each processor type that is
supported.
This manual describes the usage of RTEMS for applications written in the C
programming language. Those implementation details that are processor
dependent are provided in the Applications Supplement documents. A supplement
document which addresses specific architectural issues that affect RTEMS is
provided for each processor type that is supported.
Real-time Application Systems
=============================
Real-time application systems are a special class of
computer applications. They have a complex set of
characteristics that distinguish them from other software
problems. Generally, they must adhere to more rigorous
requirements. The correctness of the system depends not only on
the results of computations, but also on the time at which the
results are produced. The most important and complex
characteristic of real-time application systems is that they
must receive and respond to a set of external stimuli within
rigid and critical time constraints referred to as deadlines.
Systems can be buried by an avalanche of interdependent,
asynchronous or cyclical event streams.
Real-time application systems are a special class of computer applications.
They have a complex set of characteristics that distinguish them from other
software problems. Generally, they must adhere to more rigorous requirements.
The correctness of the system depends not only on the results of computations,
but also on the time at which the results are produced. The most important and
complex characteristic of real-time application systems is that they must
receive and respond to a set of external stimuli within rigid and critical time
constraints referred to as deadlines. Systems can be buried by an avalanche of
interdependent, asynchronous or cyclical event streams.
Deadlines can be further characterized as either hard
or soft based upon the value of the results when produced after
the deadline has passed. A deadline is hard if the results have
no value or if their use will result in a catastrophic event.
In contrast, results which are produced after a soft deadline
may have some value.
Deadlines can be further characterized as either hard or soft based upon the
value of the results when produced after the deadline has passed. A deadline
is hard if the results have no value or if their use will result in a
catastrophic event. In contrast, results which are produced after a soft
deadline may have some value.
Another distinguishing requirement of real-time
application systems is the ability to coordinate or manage a
large number of concurrent activities. Since software is a
synchronous entity, this presents special problems. One
instruction follows another in a repeating synchronous cycle.
Even though mechanisms have been developed to allow for the
processing of external asynchronous events, the software design
efforts required to process and manage these events and tasks
are growing more complicated.
Another distinguishing requirement of real-time application systems is the
ability to coordinate or manage a large number of concurrent activities. Since
software is a synchronous entity, this presents special problems. One
instruction follows another in a repeating synchronous cycle. Even though
mechanisms have been developed to allow for the processing of external
asynchronous events, the software design efforts required to process and manage
these events and tasks are growing more complicated.
The design process is complicated further by
spreading this activity over a set of processors instead of a
single processor. The challenges associated with designing and
building real-time application systems become very complex when
multiple processors are involved. New requirements such as
interprocessor communication channels and global resources that
must be shared between competing processors are introduced. The
ramifications of multiple processors complicate each and every
characteristic of a real-time system.
The design process is complicated further by spreading this activity over a set
of processors instead of a single processor. The challenges associated with
designing and building real-time application systems become very complex when
multiple processors are involved. New requirements such as interprocessor
communication channels and global resources that must be shared between
competing processors are introduced. The ramifications of multiple processors
complicate each and every characteristic of a real-time system.
Real-time Executive
===================
Fortunately, real-time operating systems or real-time
executives serve as a cornerstone on which to build the
application system. A real-time multitasking executive allows
an application to be cast into a set of logical, autonomous
processes or tasks which become quite manageable. Each task is
internally synchronous, but different tasks execute
independently, resulting in an asynchronous processing stream.
Tasks can be dynamically paused for many reasons resulting in a
different task being allowed to execute for a period of time.
The executive also provides an interface to other system
components such as interrupt handlers and device drivers.
System components may request the executive to allocate and
coordinate resources, and to wait for and trigger synchronizing
conditions. The executive system calls effectively extend the
CPU instruction set to support efficient multitasking. By
causing tasks to travel through well-defined state transitions,
system calls permit an application to demand-switch between
tasks in response to real-time events.
Fortunately, real-time operating systems or real-time executives serve as a
cornerstone on which to build the application system. A real-time multitasking
executive allows an application to be cast into a set of logical, autonomous
processes or tasks which become quite manageable. Each task is internally
synchronous, but different tasks execute independently, resulting in an
asynchronous processing stream. Tasks can be dynamically paused for many
reasons resulting in a different task being allowed to execute for a period of
time. The executive also provides an interface to other system components such
as interrupt handlers and device drivers. System components may request the
executive to allocate and coordinate resources, and to wait for and trigger
synchronizing conditions. The executive system calls effectively extend the
CPU instruction set to support efficient multitasking. By causing tasks to
travel through well-defined state transitions, system calls permit an
application to demand-switch between tasks in response to real-time events.
By proper grouping of responses to stimuli into
separate tasks, a system can now asynchronously switch between
independent streams of execution, directly responding to
external stimuli as they occur. This allows the system design
to meet critical performance specifications which are typically
measured by guaranteed response time and transaction throughput.
The multiprocessor extensions of RTEMS provide the features
necessary to manage the extra requirements introduced by a
system distributed across several processors. It removes the
physical barriers of processor boundaries from the world of the
system designer, enabling more critical aspects of the system to
receive the required attention. Such a system, based on an
efficient real-time, multiprocessor executive, is a more
realistic model of the outside world or environment for which it
is designed. As a result, the system will always be more
logical, efficient, and reliable.
By proper grouping of responses to stimuli into separate tasks, a system can
now asynchronously switch between independent streams of execution, directly
responding to external stimuli as they occur. This allows the system design to
meet critical performance specifications which are typically measured by
guaranteed response time and transaction throughput. The multiprocessor
extensions of RTEMS provide the features necessary to manage the extra
requirements introduced by a system distributed across several processors. It
removes the physical barriers of processor boundaries from the world of the
system designer, enabling more critical aspects of the system to receive the
required attention. Such a system, based on an efficient real-time,
multiprocessor executive, is a more realistic model of the outside world or
environment for which it is designed. As a result, the system will always be
more logical, efficient, and reliable.
By using the directives provided by RTEMS, the
real-time applications developer is freed from the problem of
controlling and synchronizing multiple tasks and processors. In
addition, one need not develop, test, debug, and document
routines to manage memory, pass messages, or provide mutual
exclusion. The developer is then able to concentrate solely on
the application. By using standard software components, the
time and cost required to develop sophisticated real-time
applications is significantly reduced.
By using the directives provided by RTEMS, the real-time applications developer
is freed from the problem of controlling and synchronizing multiple tasks and
processors. In addition, one need not develop, test, debug, and document
routines to manage memory, pass messages, or provide mutual exclusion. The
developer is then able to concentrate solely on the application. By using
standard software components, the time and cost required to develop
sophisticated real-time applications is significantly reduced.
RTEMS Application Architecture
==============================
One important design goal of RTEMS was to provide a
bridge between two critical layers of typical real-time systems.
As shown in the following figure, RTEMS serves as a buffer between the
project dependent application code and the target hardware.
Most hardware dependencies for real-time applications can be
One important design goal of RTEMS was to provide a bridge between two critical
layers of typical real-time systems. As shown in the following figure, RTEMS
serves as a buffer between the project dependent application code and the
target hardware. Most hardware dependencies for real-time applications can be
localized to the low level device drivers.
.. code:: c
.. COMMENT: .. code:: c
.. COMMENT:
.. COMMENT: +-----------------------------------------------------------+
.. COMMENT: | Application Dependent Software |
.. COMMENT: | +----------------------------------------+ |
.. COMMENT: | | Standard Application Components | |
.. COMMENT: | | +-------------+---+ |
.. COMMENT: | +---+-----------+ | | |
.. COMMENT: | | Board Support | | RTEMS | |
.. COMMENT: | | Package | | | |
.. COMMENT: +----+---------------+--------------+-----------------+-----|
.. COMMENT: | Target Hardware |
.. COMMENT: +-----------------------------------------------------------+
+-----------------------------------------------------------+
| Application Dependent Software |
| +----------------------------------------+ |
| | Standard Application Components | |
| | +-------------+---+ |
| +---+-----------+ | | |
| | Board Support | | RTEMS | |
| | Package | | | |
+----+---------------+--------------+-----------------+-----|
| Target Hardware |
+-----------------------------------------------------------+
.. figure:: rtemsarc.png
:width: 488
:height: 100px
:align: center
:alt: RTEMS Application Architecture
The RTEMS I/O interface manager provides an efficient tool for incorporating
these hardware dependencies into the system while simultaneously
providing a general mechanism to the application code that
accesses them. A well designed real-time system can benefit
from this architecture by building a rich library of standard
application components which can be used repeatedly in other
these hardware dependencies into the system while simultaneously providing a
general mechanism to the application code that accesses them. A well designed
real-time system can benefit from this architecture by building a rich library
of standard application components which can be used repeatedly in other
real-time projects.
RTEMS Internal Architecture
===========================
RTEMS can be viewed as a set of layered components that work in
harmony to provide a set of services to a real-time application
system. The executive interface presented to the application is
formed by grouping directives into logical sets called resource managers.
Functions utilized by multiple managers such as scheduling,
dispatching, and object management are provided in the executive
core. The executive core depends on a small set of CPU dependent routines.
Together these components provide a powerful run time
environment that promotes the development of efficient real-time
application systems. The following figure illustrates this organization:
RTEMS can be viewed as a set of layered components that work in harmony to
provide a set of services to a real-time application system. The executive
interface presented to the application is formed by grouping directives into
logical sets called resource managers. Functions utilized by multiple managers
such as scheduling, dispatching, and object management are provided in the
executive core. The executive core depends on a small set of CPU dependent
routines. Together these components provide a powerful run time environment
that promotes the development of efficient real-time application systems. The
following figure illustrates this organization:
.. code:: c
.. COMMENT: .. code:: c
.. COMMENT:
.. COMMENT: +-----------------------------------------------+
.. COMMENT: | RTEMS Executive Interface |
.. COMMENT: +-----------------------------------------------+
.. COMMENT: | RTEMS Core |
.. COMMENT: +-----------------------------------------------+
.. COMMENT: | CPU Dependent Code |
.. COMMENT: +-----------------------------------------------+
+-----------------------------------------------+
| RTEMS Executive Interface |
+-----------------------------------------------+
| RTEMS Core |
+-----------------------------------------------+
| CPU Dependent Code |
+-----------------------------------------------+
.. figure:: rtemspie.png
:width: 70%
:align: center
:alt: RTEMS Internal Architecture
Subsequent chapters present a detailed description of the capabilities
provided by each of the following RTEMS managers:
Subsequent chapters present a detailed description of the capabilities provided
by each of the following RTEMS managers:
- initialization
@ -223,112 +215,96 @@ provided by each of the following RTEMS managers:
User Customization and Extensibility
====================================
As thirty-two bit microprocessors have decreased in
cost, they have become increasingly common in a variety of
embedded systems. A wide range of custom and general-purpose
processor boards are based on various thirty-two bit processors.
RTEMS was designed to make no assumptions concerning the
characteristics of individual microprocessor families or of
specific support hardware. In addition, RTEMS allows the system
developer a high degree of freedom in customizing and extending
its features.
As thirty-two bit microprocessors have decreased in cost, they have become
increasingly common in a variety of embedded systems. A wide range of custom
and general-purpose processor boards are based on various thirty-two bit
processors. RTEMS was designed to make no assumptions concerning the
characteristics of individual microprocessor families or of specific support
hardware. In addition, RTEMS allows the system developer a high degree of
freedom in customizing and extending its features.
RTEMS assumes the existence of a supported
microprocessor and sufficient memory for both RTEMS and the
real-time application. Board dependent components such as
clocks, interrupt controllers, or I/O devices can be easily
integrated with RTEMS. The customization and extensibility
features allow RTEMS to efficiently support as many environments
as possible.
RTEMS assumes the existence of a supported microprocessor and sufficient memory
for both RTEMS and the real-time application. Board dependent components such
as clocks, interrupt controllers, or I/O devices can be easily integrated with
RTEMS. The customization and extensibility features allow RTEMS to efficiently
support as many environments as possible.
Portability
===========
The issue of portability was the major factor in the
creation of RTEMS. Since RTEMS is designed to isolate the
hardware dependencies in the specific board support packages,
the real-time application should be easily ported to any other
processor. The use of RTEMS allows the development of real-time
applications which can be completely independent of a particular
microprocessor architecture.
The issue of portability was the major factor in the creation of RTEMS. Since
RTEMS is designed to isolate the hardware dependencies in the specific board
support packages, the real-time application should be easily ported to any
other processor. The use of RTEMS allows the development of real-time
applications which can be completely independent of a particular microprocessor
architecture.
Memory Requirements
===================
Since memory is a critical resource in many real-time
embedded systems, RTEMS was specifically designed to automatically
leave out all services that are not required from the run-time
environment. Features such as networking, various fileystems,
and many other features are completely optional. This allows
the application designer the flexibility to tailor RTEMS to most
efficiently meet system requirements while still satisfying even
the most stringent memory constraints. As a result, the size
of the RTEMS executive is application dependent.
Since memory is a critical resource in many real-time embedded systems, RTEMS
was specifically designed to automatically leave out all services that are not
required from the run-time environment. Features such as networking, various
fileystems, and many other features are completely optional. This allows the
application designer the flexibility to tailor RTEMS to most efficiently meet
system requirements while still satisfying even the most stringent memory
constraints. As a result, the size of the RTEMS executive is application
dependent.
RTEMS requires RAM to manage each instance of an RTEMS object
that is created. Thus the more RTEMS objects an application
needs, the more memory that must be reserved. See `Configuring a System`_.
RTEMS requires RAM to manage each instance of an RTEMS object that is created.
Thus the more RTEMS objects an application needs, the more memory that must be
reserved. See Configuring a System_.
RTEMS utilizes memory for both code and data space.
Although RTEMS' data space must be in RAM, its code space can be
located in either ROM or RAM.
RTEMS utilizes memory for both code and data space. Although RTEMS' data space
must be in RAM, its code space can be located in either ROM or RAM.
Audience
========
This manual was written for experienced real-time
software developers. Although some background is provided, it
is assumed that the reader is familiar with the concepts of task
management as well as intertask communication and
synchronization. Since directives, user related data
structures, and examples are presented in C, a basic
understanding of the C programming language
is required to fully
understand the material presented. However, because of the
similarity of the Ada and C RTEMS implementations, users will
find that the use and behavior of the two implementations is
very similar. A working knowledge of the target processor is
helpful in understanding some of RTEMS' features. A thorough
understanding of the executive cannot be obtained without
studying the entire manual because many of RTEMS' concepts and
features are interrelated. Experienced RTEMS users will find
that the manual organization facilitates its use as a reference
document.
This manual was written for experienced real-time software developers.
Although some background is provided, it is assumed that the reader is familiar
with the concepts of task management as well as intertask communication and
synchronization. Since directives, user related data structures, and examples
are presented in C, a basic understanding of the C programming language is
required to fully understand the material presented. However, because of the
similarity of the Ada and C RTEMS implementations, users will find that the use
and behavior of the two implementations is very similar. A working knowledge
of the target processor is helpful in understanding some of RTEMS' features. A
thorough understanding of the executive cannot be obtained without studying the
entire manual because many of RTEMS' concepts and features are interrelated.
Experienced RTEMS users will find that the manual organization facilitates its
use as a reference document.
Conventions
===========
The following conventions are used in this manual:
- Significant words or phrases as well as all directive
names are printed in bold type.
- Significant words or phrases as well as all directive names are printed in
bold type.
- Items in bold capital letters are constants defined by
RTEMS. Each language interface provided by RTEMS includes a
file containing the standard set of constants, data types, and
structure definitions which can be incorporated into the user
application.
- Items in bold capital letters are constants defined by RTEMS. Each language
interface provided by RTEMS includes a file containing the standard set of
constants, data types, and structure definitions which can be incorporated
into the user application.
- A number of type definitions are provided by RTEMS and
can be found in rtems.h.
- A number of type definitions are provided by RTEMS and can be found in
rtems.h.
- The characters "0x" preceding a number indicates that
the number is in hexadecimal format. Any other numbers are
assumed to be in decimal format.
- The characters "0x" preceding a number indicates that the number is in
hexadecimal format. Any other numbers are assumed to be in decimal format.
Manual Organization
===================
This first chapter has presented the introductory and
background material for the RTEMS executive. The remaining
chapters of this manual present a detailed description of RTEMS
and the environment, including run time behavior, it creates for
the user.
This first chapter has presented the introductory and background material for
the RTEMS executive. The remaining chapters of this manual present a detailed
description of RTEMS and the environment, including run time behavior, it
creates for the user.
A chapter is dedicated to each manager and provides a
detailed discussion of each RTEMS manager and the directives
which it provides. The presentation format for each directive
includes the following sections:
A chapter is dedicated to each manager and provides a detailed discussion of
each RTEMS manager and the directives which it provides. The presentation
format for each directive includes the following sections:
- Calling sequence
@ -338,152 +314,136 @@ includes the following sections:
- Notes
The following provides an overview of the remainder
of this manual:
The following provides an overview of the remainder of this manual:
Chapter 2:
Key Concepts: presents an introduction to the ideas which are common
across multiple RTEMS managers.
Key Concepts: presents an introduction to the ideas which are common across
multiple RTEMS managers.
Chapter 3:
RTEMS Data Types: describes the fundamental data types shared
by the services in the RTEMS Classic API.
RTEMS Data Types: describes the fundamental data types shared by the
services in the RTEMS Classic API.
Chapter 4:
Scheduling Concepts: details the various RTEMS scheduling algorithms
and task state transitions.
Scheduling Concepts: details the various RTEMS scheduling algorithms and
task state transitions.
Chapter 5:
Initialization Manager: describes the functionality and directives
provided by the Initialization Manager.
Initialization Manager: describes the functionality and directives provided
by the Initialization Manager.
Chapter 6:
Task Manager: describes the functionality and directives provided
by the Task Manager.
Task Manager: describes the functionality and directives provided by the
Task Manager.
Chapter 7:
Interrupt Manager: describes the functionality and directives
provided by the Interrupt Manager.
Interrupt Manager: describes the functionality and directives provided by
the Interrupt Manager.
Chapter 8:
Clock Manager: describes the functionality and directives
provided by the Clock Manager.
Clock Manager: describes the functionality and directives provided by the
Clock Manager.
Chapter 9:
Timer Manager: describes the functionality and directives provided
by the Timer Manager.
Timer Manager: describes the functionality and directives provided by the
Timer Manager.
Chapter 10:
Rate Monotonic Manager: describes the functionality and directives
provided by the Rate Monotonic Manager.
Rate Monotonic Manager: describes the functionality and directives provided
by the Rate Monotonic Manager.
Chapter 11:
Semaphore Manager: describes the functionality and directives
provided by the Semaphore Manager.
Semaphore Manager: describes the functionality and directives provided by
the Semaphore Manager.
Chapter 12:
Barrier Manager: describes the functionality and directives
provided by the Barrier Manager.
Barrier Manager: describes the functionality and directives provided by the
Barrier Manager.
Chapter 13:
Message Manager: describes the functionality and directives
provided by the Message Manager.
Message Manager: describes the functionality and directives provided by the
Message Manager.
Chapter 14:
Event Manager: describes the
functionality and directives provided by the Event Manager.
Event Manager: describes the functionality and directives provided by the
Event Manager.
Chapter 15:
Signal Manager: describes the
functionality and directives provided by the Signal Manager.
Signal Manager: describes the functionality and directives provided by the
Signal Manager.
Chapter 16:
Partition Manager: describes the
functionality and directives provided by the Partition Manager.
Partition Manager: describes the functionality and directives provided by
the Partition Manager.
Chapter 17:
Region Manager: describes the
functionality and directives provided by the Region Manager.
Region Manager: describes the functionality and directives provided by the
Region Manager.
Chapter 18:
Dual-Ported Memory Manager: describes
the functionality and directives provided by the Dual-Ported
Memory Manager.
Dual-Ported Memory Manager: describes the functionality and directives
provided by the Dual-Ported Memory Manager.
Chapter 19:
I/O Manager: describes the
functionality and directives provided by the I/O Manager.
I/O Manager: describes the functionality and directives provided by the I/O
Manager.
Chapter 20:
Fatal Error Manager: describes the functionality and directives
provided by the Fatal Error Manager.
Fatal Error Manager: describes the functionality and directives provided by
the Fatal Error Manager.
Chapter 21:
Board Support Packages: defines the
functionality required of user-supplied board support packages.
Board Support Packages: defines the functionality required of user-supplied
board support packages.
Chapter 22:
User Extensions: shows the user how to
extend RTEMS to incorporate custom features.
User Extensions: shows the user how to extend RTEMS to incorporate custom
features.
Chapter 23:
Configuring a System: details the process by which one tailors RTEMS
for a particular single-processor or multiprocessor application.
Configuring a System: details the process by which one tailors RTEMS for a
particular single-processor or multiprocessor application.
Chapter 24:
Multiprocessing Manager: presents a
conceptual overview of the multiprocessing capabilities provided
by RTEMS as well as describing the Multiprocessing
Communications Interface Layer and Multiprocessing Manager
Multiprocessing Manager: presents a conceptual overview of the
multiprocessing capabilities provided by RTEMS as well as describing the
Multiprocessing Communications Interface Layer and Multiprocessing Manager
directives.
Chapter 25:
Stack Bounds Checker: presents the capabilities of the RTEMS
task stack checker which can report stack usage as well as detect
bounds violations.
Stack Bounds Checker: presents the capabilities of the RTEMS task stack
checker which can report stack usage as well as detect bounds violations.
Chapter 26:
CPU Usage Statistics: presents the capabilities of the CPU Usage
statistics gathered on a per task basis along with the mechanisms
for reporting and resetting the statistics.
CPU Usage Statistics: presents the capabilities of the CPU Usage statistics
gathered on a per task basis along with the mechanisms for reporting and
resetting the statistics.
Chapter 27:
Object Services: presents a collection of helper services useful
when manipulating RTEMS objects. These include methods to assist
in obtaining an object's name in printable form. Additional services
are provided to decompose an object Id and determine which API
and object class it belongs to.
Object Services: presents a collection of helper services useful when
manipulating RTEMS objects. These include methods to assist in obtaining an
object's name in printable form. Additional services are provided to
decompose an object Id and determine which API and object class it belongs
to.
Chapter 28:
Chains: presents the methods provided to build, iterate and
manipulate doubly-linked chains. This manager makes the
chain implementation used internally by RTEMS to user space
applications.
Chains: presents the methods provided to build, iterate and manipulate
doubly-linked chains. This manager makes the chain implementation used
internally by RTEMS to user space applications.
Chapter 29:
Timespec Helpers: presents a set of helper services useful
when manipulating POSIX ``struct timespec`` instances.
Timespec Helpers: presents a set of helper services useful when
manipulating POSIX ``struct timespec`` instances.
Chapter 30:
Constant Bandwidth Server Scheduler API.
Chapter 31:
Directive Status Codes: provides a definition of each of the
directive status codes referenced in this manual.
Directive Status Codes: provides a definition of each of the directive
status codes referenced in this manual.
Chapter 32:
Example Application: provides a template for simple RTEMS applications.
Chapter 33:
Glossary: defines terms used throughout this manual.
.. COMMENT: COPYRIGHT (c) 1988-2007.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
.. COMMENT: The following figure was replaced with an ASCII equivalent.
.. COMMENT: Figure 2-1 Object ID Composition

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@ -1,144 +1,123 @@
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
Preface
#######
In recent years, the cost required to develop a
software product has increased significantly while the target
hardware costs have decreased. Now a larger portion of money is
expended in developing, using, and maintaining software. The
trend in computing costs is the complete dominance of software
over hardware costs. Because of this, it is necessary that
formal disciplines be established to increase the probability
that software is characterized by a high degree of correctness,
maintainability, and portability. In addition, these
disciplines must promote practices that aid in the consistent
and orderly development of a software system within schedule and
budgetary constraints. To be effective, these disciplines must
adopt standards which channel individual software efforts toward
a common goal.
In recent years, the cost required to develop a software product has increased
significantly while the target hardware costs have decreased. Now a larger
portion of money is expended in developing, using, and maintaining software.
The trend in computing costs is the complete dominance of software over
hardware costs. Because of this, it is necessary that formal disciplines be
established to increase the probability that software is characterized by a
high degree of correctness, maintainability, and portability. In addition,
these disciplines must promote practices that aid in the consistent and orderly
development of a software system within schedule and budgetary constraints. To
be effective, these disciplines must adopt standards which channel individual
software efforts toward a common goal.
The push for standards in the software development
field has been met with various degrees of success. The
Microprocessor Operating Systems Interfaces (MOSI) effort has
experienced only limited success. As popular as the UNIX
operating system has grown, the attempt to develop a standard
interface definition to allow portable application development
has only recently begun to produce the results needed in this
area. Unfortunately, very little effort has been expended to
provide standards addressing the needs of the real-time
community. Several organizations have addressed this need
during recent years.
The push for standards in the software development field has been met with
various degrees of success. The Microprocessor Operating Systems Interfaces
(MOSI) effort has experienced only limited success. As popular as the UNIX
operating system has grown, the attempt to develop a standard interface
definition to allow portable application development has only recently begun to
produce the results needed in this area. Unfortunately, very little effort has
been expended to provide standards addressing the needs of the real-time
community. Several organizations have addressed this need during recent years.
The Real Time Executive Interface Definition (RTEID)
was developed by Motorola with technical input from Software
Components Group. RTEID was adopted by the VMEbus International
Trade Association (VITA) as a baseline draft for their proposed
standard multiprocessor, real-time executive interface, Open
Real-Time Kernel Interface Definition (ORKID). These two groups
are currently working together with the IEEE P1003.4 committee
to insure that the functionality of their proposed standards is
adopted as the real-time extensions to POSIX.
The Real Time Executive Interface Definition (RTEID) was developed by Motorola
with technical input from Software Components Group. RTEID was adopted by the
VMEbus International Trade Association (VITA) as a baseline draft for their
proposed standard multiprocessor, real-time executive interface, Open Real-Time
Kernel Interface Definition (ORKID). These two groups are currently working
together with the IEEE P1003.4 committee to insure that the functionality of
their proposed standards is adopted as the real-time extensions to POSIX.
This emerging standard defines an interface for the
development of real-time software to ease the writing of
real-time application programs that are directly portable across
multiple real-time executive implementations. This interface
includes both the source code interfaces and run-time behavior
as seen by a real-time application. It does not include the
details of how a kernel implements these functions. The
standard's goal is to serve as a complete definition of external
interfaces so that application code that conforms to these
interfaces will execute properly in all real-time executive
environments. With the use of a standards compliant executive,
routines that acquire memory blocks, create and manage message
queues, establish and use semaphores, and send and receive
signals need not be redeveloped for a different real-time
environment as long as the new environment is compliant with the
standard. Software developers need only concentrate on the
hardware dependencies of the real-time system. Furthermore,
most hardware dependencies for real-time applications can be
localized to the device drivers.
This emerging standard defines an interface for the development of real-time
software to ease the writing of real-time application programs that are
directly portable across multiple real-time executive implementations. This
interface includes both the source code interfaces and run-time behavior as
seen by a real-time application. It does not include the details of how a
kernel implements these functions. The standard's goal is to serve as a
complete definition of external interfaces so that application code that
conforms to these interfaces will execute properly in all real-time executive
environments. With the use of a standards compliant executive, routines that
acquire memory blocks, create and manage message queues, establish and use
semaphores, and send and receive signals need not be redeveloped for a
different real-time environment as long as the new environment is compliant
with the standard. Software developers need only concentrate on the hardware
dependencies of the real-time system. Furthermore, most hardware dependencies
for real-time applications can be localized to the device drivers.
A compliant executive provides simple and flexible
real-time multiprocessing. It easily lends itself to both
tightly-coupled and loosely-coupled configurations (depending on
the system hardware configuration). Objects such as tasks,
queues, events, signals, semaphores, and memory blocks can be
designated as global objects and accessed by any task regardless
of which processor the object and the accessing task reside.
A compliant executive provides simple and flexible real-time multiprocessing.
It easily lends itself to both tightly-coupled and loosely-coupled
configurations (depending on the system hardware configuration). Objects such
as tasks, queues, events, signals, semaphores, and memory blocks can be
designated as global objects and accessed by any task regardless of which
processor the object and the accessing task reside.
The acceptance of a standard for real-time executives
will produce the same advantages enjoyed from the push for UNIX
standardization by AT&T's System V Interface Definition and
IEEE's POSIX efforts. A compliant multiprocessing executive
will allow close coupling between UNIX systems and real-time
executives to provide the many benefits of the UNIX development
environment to be applied to real-time software development.
Together they provide the necessary laboratory environment to
implement real-time, distributed, embedded systems using a wide
variety of computer architectures.
The acceptance of a standard for real-time executives will produce the same
advantages enjoyed from the push for UNIX standardization by AT&T's System V
Interface Definition and IEEE's POSIX efforts. A compliant multiprocessing
executive will allow close coupling between UNIX systems and real-time
executives to provide the many benefits of the UNIX development environment to
be applied to real-time software development. Together they provide the
necessary laboratory environment to implement real-time, distributed, embedded
systems using a wide variety of computer architectures.
A study was completed in 1988, within the Research,
Development, and Engineering Center, U.S. Army Missile Command,
which compared the various aspects of the Ada programming
language as they related to the application of Ada code in
distributed and/or multiple processing systems. Several
critical conclusions were derived from the study. These
conclusions have a major impact on the way the Army develops
application software for embedded applications. These impacts
apply to both in-house software development and contractor
developed software.
A study was completed in 1988, within the Research, Development, and
Engineering Center, U.S. Army Missile Command, which compared the various
aspects of the Ada programming language as they related to the application of
Ada code in distributed and/or multiple processing systems. Several critical
conclusions were derived from the study. These conclusions have a major impact
on the way the Army develops application software for embedded
applications. These impacts apply to both in-house software development and
contractor developed software.
A conclusion of the analysis, which has been
previously recognized by other agencies attempting to utilize
Ada in a distributed or multiprocessing environment, is that the
Ada programming language does not adequately support
multiprocessing. Ada does provide a mechanism for
multi-tasking, however, this capability exists only for a single
processor system. The language also does not have inherent
capabilities to access global named variables, flags or program
code. These critical features are essential in order for data
to be shared between processors. However, these drawbacks do
have workarounds which are sometimes awkward and defeat the
intent of software maintainability and portability goals.
A conclusion of the analysis, which has been previously recognized by other
agencies attempting to utilize Ada in a distributed or multiprocessing
environment, is that the Ada programming language does not adequately support
multiprocessing. Ada does provide a mechanism for multi-tasking, however, this
capability exists only for a single processor system. The language also does
not have inherent capabilities to access global named variables, flags or
program code. These critical features are essential in order for data to be
shared between processors. However, these drawbacks do have workarounds which
are sometimes awkward and defeat the intent of software maintainability and
portability goals.
Another conclusion drawn from the analysis, was that
the run time executives being delivered with the Ada compilers
were too slow and inefficient to be used in modern missile
systems. A run time executive is the core part of the run time
system code, or operating system code, that controls task
scheduling, input/output management and memory management.
Traditionally, whenever efficient executive (also known as
kernel) code was required by the application, the user developed
in-house software. This software was usually written in
assembly language for optimization.
Another conclusion drawn from the analysis, was that the run time executives
being delivered with the Ada compilers were too slow and inefficient to be used
in modern missile systems. A run time executive is the core part of the run
time system code, or operating system code, that controls task scheduling,
input/output management and memory management. Traditionally, whenever
efficient executive (also known as kernel) code was required by the
application, the user developed in-house software. This software was usually
written in assembly language for optimization.
Because of this shortcoming in the Ada programming
language, software developers in research and development and
contractors for project managed systems, are mandated by
technology to purchase and utilize off-the-shelf third party
kernel code. The contractor, and eventually the Government,
must pay a licensing fee for every copy of the kernel code used
in an embedded system.
Because of this shortcoming in the Ada programming language, software
developers in research and development and contractors for project managed
systems, are mandated by technology to purchase and utilize off-the-shelf third
party kernel code. The contractor, and eventually the Government, must pay a
licensing fee for every copy of the kernel code used in an embedded system.
The main drawback to this development environment is
that the Government does not own, nor has the right to modify
code contained within the kernel. V&V techniques in this
situation are more difficult than if the complete source code
were available. Responsibility for system failures due to faulty
software is yet another area to be resolved under this
environment.
The main drawback to this development environment is that the Government does
not own, nor has the right to modify code contained within the kernel. V&V
techniques in this situation are more difficult than if the complete source
code were available. Responsibility for system failures due to faulty software
is yet another area to be resolved under this environment.
The Guidance and Control Directorate began a software
development effort to address these problems. A project to
develop an experimental run time kernel was begun that will
eliminate the major drawbacks of the Ada programming language
mentioned above. The Real Time Executive for Multiprocessor Systems
(RTEMS) provides full capabilities for management of tasks,
interrupts, time, and multiple processors in addition to those
features typical of generic operating systems. The code is
Government owned, so no licensing fees are necessary. RTEMS has
been implemented in both the Ada and C programming languages.
It has been ported to the following processor families:
The Guidance and Control Directorate began a software development effort to
address these problems. A project to develop an experimental run time kernel
was begun that will eliminate the major drawbacks of the Ada programming
language mentioned above. The Real Time Executive for Multiprocessor Systems
(RTEMS) provides full capabilities for management of tasks, interrupts, time,
and multiple processors in addition to those features typical of generic
operating systems. The code is Government owned, so no licensing fees are
necessary. RTEMS has been implemented in both the Ada and C programming
languages. It has been ported to the following processor families:
- Adapteva Epiphany
- Altera NIOS II
@ -162,6 +141,10 @@ It has been ported to the following processor families:
- MIPS
- Moxie Processor
- OpenRISC
- PowerPC
- Renesas (formerly Hitachi) SuperH
@ -172,38 +155,20 @@ It has been ported to the following processor families:
- SPARC v7, v8, and V9
Support for other processor families, including RISC, CISC, and DSP, is
planned. Since almost all of RTEMS is written in a high level language,
ports to additional processor families require minimal effort.
Since almost all of RTEMS is written in a high level language, ports to
additional processor families require minimal effort.
RTEMS multiprocessor support is capable of handling
either homogeneous or heterogeneous systems. The kernel
automatically compensates for architectural differences (byte
swapping, etc.) between processors. This allows a much easier
transition from one processor family to another without a major
system redesign.
RTEMS multiprocessor support is capable of handling either homogeneous or
heterogeneous systems. The kernel automatically compensates for architectural
differences (byte swapping, etc.) between processors. This allows a much
easier transition from one processor family to another without a major system
redesign.
Since the proposed standards are still in draft form,
RTEMS cannot and does not claim compliance. However, the status
of the standard is being carefully monitored to guarantee that
RTEMS provides the functionality specified in the standard.
Once approved, RTEMS will be made compliant.
This document is a detailed users guide for a
functionally compliant real-time multiprocessor executive. It
describes the user interface and run-time behavior of Release
4.10.99.0 of the C interface
to RTEMS.
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
.. COMMENT: This chapter is missing the following figures:
.. COMMENT: Figure 1-1 RTEMS Application Architecture
.. COMMENT: Figure 1-2 RTEMS Internal Architecture
Since the proposed standards are still in draft form, RTEMS cannot and does not
claim compliance. However, the status of the standard is being carefully
monitored to guarantee that RTEMS provides the functionality specified in the
standard. Once approved, RTEMS will be made compliant.
This document is a detailed users guide for a functionally compliant real-time
multiprocessor executive. It describes the user interface and run-time
behavior of Release 4.10.99.0 of the C interface to RTEMS.

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.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
RTEMS Data Types
################
Introduction
============
This chapter contains a complete list of the RTEMS primitive
data types in alphabetical order. This is intended to be
an overview and the user is encouraged to look at the appropriate
chapters in the manual for more information about the
usage of the various data types.
This chapter contains a complete list of the RTEMS primitive data types in
alphabetical order. This is intended to be an overview and the user is
encouraged to look at the appropriate chapters in the manual for more
information about the usage of the various data types.
List of Data Types
==================
The following is a complete list of the RTEMS primitive
data types in alphabetical order:
The following is a complete list of the RTEMS primitive data types in
alphabetical order:
- .. index:: rtems_address
.. index:: rtems_address
``rtems_address`` is the data type used to manage
addresses. It is equivalent to
a "void \*" pointer.
``rtems_address``
The data type used to manage addresses. It is equivalent to a ``void *``
pointer.
- .. index:: rtems_asr
.. index:: rtems_asr
``rtems_asr`` is the return type for an
RTEMS ASR.
``rtems_asr``
The return type for an RTEMS ASR.
- .. index:: rtems_asr_entry
.. index:: rtems_asr_entry
``rtems_asr_entry`` is the address of
the entry point to an RTEMS ASR.
``rtems_asr_entry``
The address of the entry point to an RTEMS ASR.
- .. index:: rtems_attribute
.. index:: rtems_attribute
``rtems_attribute`` is the data type used
to manage the attributes for RTEMS objects. It is primarily
used as an argument to object create routines to specify
``rtems_attribute``
The data type used to manage the attributes for RTEMS objects. It is
primarily used as an argument to object create routines to specify
characteristics of the new object.
- .. index:: rtems_boolean
.. index:: rtems_boolean
``rtems_boolean`` may only take on the
values of ``TRUE`` and ``FALSE``.
This type is deprecated. Use "bool" instead.
``rtems_boolean``
May only take on the values of ``TRUE`` and ``FALSE``. This type is
deprecated. Use ``bool`` instead.
- .. index:: rtems_context
.. index:: rtems_context
``rtems_context`` is the CPU dependent
data structure used to manage the integer and system
``rtems_context``
The CPU dependent data structure used to manage the integer and system
register portion of each task's context.
- .. index:: rtems_context_fp
.. index:: rtems_context_fp
``rtems_context_fp`` is the CPU dependent
data structure used to manage the floating point portion of
``rtems_context_fp``
The CPU dependent data structure used to manage the floating point portion of
each task's context.
- .. index:: rtems_device_driver
.. index:: rtems_device_driver
``rtems_device_driver`` is the
return type for a RTEMS device driver routine.
``rtems_device_driver``
The return type for a RTEMS device driver routine.
- .. index:: rtems_device_driver_entry
.. index:: rtems_device_driver_entry
``rtems_device_driver_entry`` is the
entry point to a RTEMS device driver routine.
``rtems_device_driver_entry``
The entry point to a RTEMS device driver routine.
- .. index:: rtems_device_major_number
.. index:: rtems_device_major_number
``rtems_device_major_number`` is the
data type used to manage device major numbers.
``rtems_device_major_number``
The data type used to manage device major numbers.
- .. index:: rtems_device_minor_number
.. index:: rtems_device_minor_number
``rtems_device_minor_number`` is the
data type used to manage device minor numbers.
``rtems_device_minor_number``
The data type used to manage device minor numbers.
- .. index:: rtems_double
.. index:: rtems_double
``rtems_double`` is the RTEMS data
type that corresponds to double precision floating point
on the target hardware.
This type is deprecated. Use "double" instead.
``rtems_double``
The RTEMS data type that corresponds to double precision floating point on
the target hardware. This type is deprecated. Use ``double`` instead.
- .. index:: rtems_event_set
.. index:: rtems_event_set
``rtems_event_set`` is the data
type used to manage and manipulate RTEMS event sets
with the Event Manager.
``rtems_event_set``
The data type used to manage and manipulate RTEMS event sets with the Event
Manager.
- .. index:: rtems_extension
.. index:: rtems_extension
``rtems_extension`` is the return type
for RTEMS user extension routines.
``rtems_extension``
The return type for RTEMS user extension routines.
- .. index:: rtems_fatal_extension
.. index:: rtems_fatal_extension
``rtems_fatal_extension`` is the
entry point for a fatal error user extension handler routine.
``rtems_fatal_extension``
- .. index:: rtems_id
The entry point for a fatal error user extension handler routine.
``rtems_id`` is the data type used
to manage and manipulate RTEMS object IDs.
.. index:: rtems_id
- .. index:: rtems_interrupt_frame
``rtems_id``
The data type used to manage and manipulate RTEMS object IDs.
``rtems_interrupt_frame`` is the
data structure that defines the format of the interrupt
stack frame as it appears to a user ISR. This data
structure may not be defined on all ports.
.. index:: rtems_interrupt_frame
- .. index:: rtems_interrupt_level
``rtems_interrupt_frame``
The data structure that defines the format of the interrupt stack frame as it
appears to a user ISR. This data structure may not be defined on all ports.
``rtems_interrupt_level`` is the
data structure used with the ``rtems_interrupt_disable``,``rtems_interrupt_enable``, and``rtems_interrupt_flash`` routines. This
data type is CPU dependent and usually corresponds to
the contents of the processor register containing
the interrupt mask level.
.. index:: rtems_interrupt_level
- .. index:: rtems_interval
``rtems_interrupt_level``
``rtems_interval`` is the data
type used to manage and manipulate time intervals.
Intervals are non-negative integers used to measure
the length of time in clock ticks.
The data structure used with the ``rtems_interrupt_disable``,
``rtems_interrupt_enable``, and ``rtems_interrupt_flash`` routines. This
data type is CPU dependent and usually corresponds to the contents of the
processor register containing the interrupt mask level.
- .. index:: rtems_isr
.. index:: rtems_interval
``rtems_isr`` is the return type
of a function implementing an RTEMS ISR.
``rtems_interval``
The data type used to manage and manipulate time intervals. Intervals are
non-negative integers used to measure the length of time in clock ticks.
- .. index:: rtems_isr_entry
.. index:: rtems_isr
``rtems_isr_entry`` is the address of
the entry point to an RTEMS ISR. It is equivalent to the
``rtems_isr``
The return type of a function implementing an RTEMS ISR.
.. index:: rtems_isr_entry
``rtems_isr_entry``
The address of the entry point to an RTEMS ISR. It is equivalent to the
entry point of the function implementing the ISR.
- .. index:: rtems_mp_packet_classes
.. index:: rtems_mp_packet_classes
``rtems_mp_packet_classes`` is the
enumerated type which specifies the categories of
multiprocessing messages. For example, one of the
classes is for messages that must be processed by
the Task Manager.
``rtems_mp_packet_classes``
The enumerated type which specifies the categories of multiprocessing
messages. For example, one of the classes is for messages that must be
processed by the Task Manager.
- .. index:: rtems_mode
.. index:: rtems_mode
``rtems_mode`` is the data type
used to manage and dynamically manipulate the execution
mode of an RTEMS task.
``rtems_mode``
The data type used to manage and dynamically manipulate the execution mode of
an RTEMS task.
- .. index:: rtems_mpci_entry
.. index:: rtems_mpci_entry
``rtems_mpci_entry`` is the return type
of an RTEMS MPCI routine.
``rtems_mpci_entry``
The return type of an RTEMS MPCI routine.
- .. index:: rtems_mpci_get_packet_entry
.. index:: rtems_mpci_get_packet_entry
``rtems_mpci_get_packet_entry`` is the address of
the entry point to the get packet routine for an MPCI implementation.
``rtems_mpci_get_packet_entry``
The address of the entry point to the get packet routine for an MPCI
implementation.
- .. index:: rtems_mpci_initialization_entry
.. index:: rtems_mpci_initialization_entry
``rtems_mpci_initialization_entry`` is the address of
the entry point to the initialization routine for an MPCI implementation.
``rtems_mpci_initialization_entry``
The address of the entry point to the initialization routine for an MPCI
implementation.
- .. index:: rtems_mpci_receive_packet_entry
.. index:: rtems_mpci_receive_packet_entry
``rtems_mpci_receive_packet_entry`` is the address of
the entry point to the receive packet routine for an MPCI implementation.
``rtems_mpci_receive_packet_entry``
The address of the entry point to the receive packet routine for an MPCI
implementation.
- .. index:: rtems_mpci_return_packet_entry
.. index:: rtems_mpci_return_packet_entry
``rtems_mpci_return_packet_entry`` is the address of
the entry point to the return packet routine for an MPCI implementation.
``rtems_mpci_return_packet_entry``
The address of the entry point to the return packet routine for an MPCI
implementation.
- .. index:: rtems_mpci_send_packet_entry
.. index:: rtems_mpci_send_packet_entry
``rtems_mpci_send_packet_entry`` is the address of
the entry point to the send packet routine for an MPCI implementation.
``rtems_mpci_send_packet_entry``
The address of the entry point to the send packet routine for an MPCI
implementation.
- .. index:: rtems_mpci_table
.. index:: rtems_mpci_table
``rtems_mpci_table`` is the data structure
containing the configuration information for an MPCI.
``rtems_mpci_table``
The data structure containing the configuration information for an MPCI.
- .. index:: rtems_name
.. index:: rtems_name
``rtems_name`` is the data type used to
contain the name of a Classic API object. It is an unsigned
thirty-two bit integer which can be treated as a numeric
value or initialized using ``rtems_build_name`` to
contain four ASCII characters.
``rtems_name``
The data type used to contain the name of a Classic API object. It is an
unsigned thirty-two bit integer which can be treated as a numeric value or
initialized using ``rtems_build_name`` to contain four ASCII characters.
- .. index:: rtems_option
.. index:: rtems_option
``rtems_option`` is the data type
used to specify which behavioral options the caller desires.
It is commonly used with potentially blocking directives to specify
whether the caller is willing to block or return immediately with an error
indicating that the resource was not available.
``rtems_option``
The data type used to specify which behavioral options the caller desires.
It is commonly used with potentially blocking directives to specify whether
the caller is willing to block or return immediately with an error indicating
that the resource was not available.
- .. index:: rtems_packet_prefix
.. index:: rtems_packet_prefix
``rtems_packet_prefix`` is the data structure
that defines the first bytes in every packet sent between nodes
in an RTEMS multiprocessor system. It contains routing information
``rtems_packet_prefix``
The data structure that defines the first bytes in every packet sent between
nodes in an RTEMS multiprocessor system. It contains routing information
that is expected to be used by the MPCI layer.
- .. index:: rtems_signal_set
.. index:: rtems_signal_set
``rtems_signal_set`` is the data
type used to manage and manipulate RTEMS signal sets
with the Signal Manager.
``rtems_signal_set``
The data type used to manage and manipulate RTEMS signal sets with the Signal
Manager.
- .. index:: int8_t
.. index:: int8_t
``int8_t`` is the C99 data type that corresponds to signed eight
bit integers. This data type is defined by RTEMS in a manner that
ensures it is portable across different target processors.
``int8_t``
The C99 data type that corresponds to signed eight bit integers. This data
type is defined by RTEMS in a manner that ensures it is portable across
different target processors.
- .. index:: int16_t
.. index:: int16_t
``int16_t`` is the C99 data type that corresponds to signed
sixteen bit integers. This data type is defined by RTEMS in a manner
that ensures it is portable across different target processors.
``int16_t``
The C99 data type that corresponds to signed sixteen bit integers. This data
type is defined by RTEMS in a manner that ensures it is portable across
different target processors.
- .. index:: int32_t
.. index:: int32_t
``int32_t`` is the C99 data type that corresponds to signed
thirty-two bit integers. This data type is defined by RTEMS in a manner
that ensures it is portable across different target processors.
``int32_t``
The C99 data type that corresponds to signed thirty-two bit integers. This
data type is defined by RTEMS in a manner that ensures it is portable across
different target processors.
- .. index:: int64_t
.. index:: int64_t
``int64_t`` is the C99 data type that corresponds to signed
sixty-four bit integers. This data type is defined by RTEMS in a manner
that ensures it is portable across different target processors.
``int64_t``
The C99 data type that corresponds to signed sixty-four bit integers. This
data type is defined by RTEMS in a manner that ensures it is portable across
different target processors.
- .. index:: rtems_single
.. index:: rtems_single
``rtems_single`` is the RTEMS data
type that corresponds to single precision floating point
on the target hardware.
This type is deprecated. Use "float" instead.
``rtems_single``
The RTEMS data type that corresponds to single precision floating point on
the target hardware. This type is deprecated. Use ``float`` instead.
- .. index:: rtems_status_codes
.. index:: rtems_status_codes
``rtems_status_codes`` is the return type for most
RTEMS services. This is an enumerated type of approximately twenty-five
values. In general, when a service returns a particular status code, it
indicates that a very specific error condition has occurred.
``rtems_status_codes``
The return type for most RTEMS services. This is an enumerated type of
approximately twenty-five values. In general, when a service returns a
particular status code, it indicates that a very specific error condition has
occurred.
- .. index:: rtems_task
.. index:: rtems_task
``rtems_task`` is the return type for an
RTEMS Task.
``rtems_task``
The return type for an RTEMS Task.
- .. index:: rtems_task_argument
.. index:: rtems_task_argument
``rtems_task_argument`` is the data
type for the argument passed to each RTEMS task. In RTEMS 4.7
and older, this is an unsigned thirty-two bit integer. In
RTEMS 4.8 and newer, this is based upon the C99 type ``uintptr_t``
which is guaranteed to be an integer large enough to hold a
pointer on the target architecture.
``rtems_task_argument``
The data type for the argument passed to each RTEMS task. In RTEMS 4.7 and
older, this is an unsigned thirty-two bit integer. In RTEMS 4.8 and newer,
this is based upon the C99 type ``uintptr_t`` which is guaranteed to be an
integer large enough to hold a pointer on the target architecture.
- .. index:: rtems_task_begin_extension
.. index:: rtems_task_begin_extension
``rtems_task_begin_extension`` is the
entry point for a task beginning execution user extension handler routine.
``rtems_task_begin_extension``
The entry point for a task beginning execution user extension handler
routine.
- .. index:: rtems_task_create_extension
.. index:: rtems_task_create_extension
``rtems_task_create_extension`` is the
entry point for a task creation execution user extension handler routine.
``rtems_task_create_extension``
The entry point for a task creation execution user extension handler routine.
- .. index:: rtems_task_delete_extension
.. index:: rtems_task_delete_extension
``rtems_task_delete_extension`` is the
entry point for a task deletion user extension handler routine.
``rtems_task_delete_extension``
The entry point for a task deletion user extension handler routine.
- .. index:: rtems_task_entry
.. index:: rtems_task_entry
``rtems_task_entry`` is the address of
the entry point to an RTEMS ASR. It is equivalent to the
``rtems_task_entry``
The address of the entry point to an RTEMS ASR. It is equivalent to the
entry point of the function implementing the ASR.
- .. index:: rtems_task_exitted_extension
.. index:: rtems_task_exitted_extension
``rtems_task_exitted_extension`` is the
entry point for a task exitted user extension handler routine.
``rtems_task_exitted_extension``
The entry point for a task exitted user extension handler routine.
- .. index:: rtems_task_priority
.. index:: rtems_task_priority
``rtems_task_priority`` is the data type
used to manage and manipulate task priorities.
``rtems_task_priority``
The data type used to manage and manipulate task priorities.
- .. index:: rtems_task_restart_extension
.. index:: rtems_task_restart_extension
``rtems_task_restart_extension`` is the
entry point for a task restart user extension handler routine.
``rtems_task_restart_extension``
The entry point for a task restart user extension handler routine.
- .. index:: rtems_task_start_extension
.. index:: rtems_task_start_extension
``rtems_task_start_extension`` is the
entry point for a task start user extension handler routine.
``rtems_task_start_extension``
The entry point for a task start user extension handler routine.
- .. index:: rtems_task_switch_extension
.. index:: rtems_task_switch_extension
``rtems_task_switch_extension`` is the
entry point for a task context switch user extension handler routine.
``rtems_task_switch_extension``
The entry point for a task context switch user extension handler routine.
- .. index:: rtems_tcb
.. index:: rtems_tcb
``rtems_tcb`` is the data structure associated
with each task in an RTEMS system.
``rtems_tcb``
The data structure associated with each task in an RTEMS system.
- .. index:: rtems_time_of_day
.. index:: rtems_time_of_day
``rtems_time_of_day`` is the data structure
used to manage and manipulate calendar time in RTEMS.
``rtems_time_of_day``
The data structure used to manage and manipulate calendar time in RTEMS.
- .. index:: rtems_timer_service_routine
.. index:: rtems_timer_service_routine
``rtems_timer_service_routine`` is the
return type for an RTEMS Timer Service Routine.
``rtems_timer_service_routine``
The return type for an RTEMS Timer Service Routine.
- .. index:: rtems_timer_service_routine_entry
.. index:: rtems_timer_service_routine_entry
``rtems_timer_service_routine_entry`` is the address of
the entry point to an RTEMS TSR. It is equivalent to the
``rtems_timer_service_routine_entry``
The address of the entry point to an RTEMS TSR. It is equivalent to the
entry point of the function implementing the TSR.
- .. index:: rtems_vector_number
.. index:: rtems_vector_number
``rtems_vector_number`` is the data
type used to manage and manipulate interrupt vector numbers.
``rtems_vector_number``
The data type used to manage and manipulate interrupt vector numbers.
- .. index:: uint8_t
.. index:: uint8_t
``uint8_t`` is the C99 data type that corresponds to unsigned
eight bit integers. This data type is defined by RTEMS in a manner that
ensures it is portable across different target processors.
``uint8_t``
The C99 data type that corresponds to unsigned eight bit integers. This data
type is defined by RTEMS in a manner that ensures it is portable across
different target processors.
- .. index:: uint16_t
.. index:: uint16_t
``uint16_t`` is the C99 data type that corresponds to unsigned
sixteen bit integers. This data type is defined by RTEMS in a manner
that ensures it is portable across different target processors.
``uint16_t``
The C99 data type that corresponds to unsigned sixteen bit integers. This
data type is defined by RTEMS in a manner that ensures it is portable across
different target processors.
- .. index:: uint32_t
.. index:: uint32_t
``uint32_t`` is the C99 data type that corresponds to unsigned
thirty-two bit integers. This data type is defined by RTEMS in a manner
that ensures it is portable across different target processors.
``uint32_t``
The C99 data type that corresponds to unsigned thirty-two bit integers. This
data type is defined by RTEMS in a manner that ensures it is portable across
different target processors.
- .. index:: uint64_t
.. index:: uint64_t
``uint64_t`` is the C99 data type that corresponds to unsigned
sixty-four bit integers. This data type is defined by RTEMS in a manner
that ensures it is portable across different target processors.
``uint64_t``
The C99 data type that corresponds to unsigned sixty-four bit integers. This
data type is defined by RTEMS in a manner that ensures it is portable across
different target processors.
- .. index:: uintptr_t
``uintptr_t`` is the C99 data type that corresponds to the
unsigned integer type that is of sufficient size to represent addresses
as unsigned integers. This data type is defined by RTEMS in a manner
that ensures it is portable across different target processors.
.. COMMENT: COPYRIGHT (c) 1988-2011.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
.. index:: uintptr_t
``uintptr_t``
The C99 data type that corresponds to the unsigned integer type that is of
sufficient size to represent addresses as unsigned integers. This data type
is defined by RTEMS in a manner that ensures it is portable across different
target processors.

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c_user/scheduling_concepts.rst
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@ -1,3 +1,7 @@
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
Scheduling Concepts
###################
@ -7,102 +11,101 @@ Scheduling Concepts
Introduction
============
The concept of scheduling in real-time systems dictates the ability to
provide immediate response to specific external events, particularly
the necessity of scheduling tasks to run within a specified time limit
after the occurrence of an event. For example, software embedded in
life-support systems used to monitor hospital patients must take instant
action if a change in the patient's status is detected.
The concept of scheduling in real-time systems dictates the ability to provide
immediate response to specific external events, particularly the necessity of
scheduling tasks to run within a specified time limit after the occurrence of
an event. For example, software embedded in life-support systems used to
monitor hospital patients must take instant action if a change in the patient's
status is detected.
The component of RTEMS responsible for providing this capability is
appropriately called the scheduler. The scheduler's sole purpose is
to allocate the all important resource of processor time to the various
tasks competing for attention.
appropriately called the scheduler. The scheduler's sole purpose is to
allocate the all important resource of processor time to the various tasks
competing for attention.
Scheduling Algorithms
=====================
.. index:: scheduling algorithms
RTEMS provides a plugin framework which allows it to support
multiple scheduling algorithms. RTEMS now includes multiple
scheduling algorithms in the SuperCore and the user can select which
of these they wish to use in their application. In addition,
the user can implement their own scheduling algorithm and
configure RTEMS to use it.
RTEMS provides a plugin framework which allows it to support multiple
scheduling algorithms. RTEMS now includes multiple scheduling algorithms in the
SuperCore and the user can select which of these they wish to use in their
application. In addition, the user can implement their own scheduling
algorithm and configure RTEMS to use it.
Supporting multiple scheduling algorithms gives the end user the
option to select the algorithm which is most appropriate to their use
case. Most real-time operating systems schedule tasks using a priority
based algorithm, possibly with preemption control. The classic
RTEMS scheduling algorithm which was the only algorithm available
in RTEMS 4.10 and earlier, is a priority based scheduling algorithm.
This scheduling algoritm is suitable for single core (e.g. non-SMP)
systems and is now known as the *Deterministic Priority Scheduler*.
Unless the user configures another scheduling algorithm, RTEMS will use
this on single core systems.
Supporting multiple scheduling algorithms gives the end user the option to
select the algorithm which is most appropriate to their use case. Most
real-time operating systems schedule tasks using a priority based algorithm,
possibly with preemption control. The classic RTEMS scheduling algorithm which
was the only algorithm available in RTEMS 4.10 and earlier, is a priority based
scheduling algorithm. This scheduling algoritm is suitable for single core
(e.g. non-SMP) systems and is now known as the *Deterministic Priority
Scheduler*. Unless the user configures another scheduling algorithm, RTEMS
will use this on single core systems.
Priority Scheduling
-------------------
.. index:: priority scheduling
When using priority based scheduling, RTEMS allocates the processor using
a priority-based, preemptive algorithm augmented to provide round-robin
characteristics within individual priority groups. The goal of this
algorithm is to guarantee that the task which is executing on the
processor at any point in time is the one with the highest priority
among all tasks in the ready state.
When using priority based scheduling, RTEMS allocates the processor using a
priority-based, preemptive algorithm augmented to provide round-robin
characteristics within individual priority groups. The goal of this algorithm
is to guarantee that the task which is executing on the processor at any point
in time is the one with the highest priority among all tasks in the ready
state.
When a task is added to the ready chain, it is placed behind all other
tasks of the same priority. This rule provides a round-robin within
priority group scheduling characteristic. This means that in a group of
equal priority tasks, tasks will execute in the order they become ready
or FIFO order. Even though there are ways to manipulate and adjust task
priorities, the most important rule to remember is:
When a task is added to the ready chain, it is placed behind all other tasks of
the same priority. This rule provides a round-robin within priority group
scheduling characteristic. This means that in a group of equal priority tasks,
tasks will execute in the order they become ready or FIFO order. Even though
there are ways to manipulate and adjust task priorities, the most important
rule to remember is:
- *Priority based scheduling algorithms will always select the
highest priority task that is ready to run when allocating the processor
to a task.*
.. note::
Priority scheduling is the most commonly used scheduling algorithm.
It should be used by applications in which multiple tasks contend for
CPU time or other resources and there is a need to ensure certain tasks
are given priority over other tasks.
Priority based scheduling algorithms will always select the highest priority
task that is ready to run when allocating the processor to a task.
Priority scheduling is the most commonly used scheduling algorithm. It should
be used by applications in which multiple tasks contend for CPU time or other
resources and there is a need to ensure certain tasks are given priority over
other tasks.
There are a few common methods of accomplishing the mechanics of this
algorithm. These ways involve a list or chain of tasks in the ready state.
- The least efficient method is to randomly place tasks in the ready
chain forcing the scheduler to scan the entire chain to determine which
task receives the processor.
- The least efficient method is to randomly place tasks in the ready chain
forcing the scheduler to scan the entire chain to determine which task
receives the processor.
- A more efficient method is to schedule the task by placing it
in the proper place on the ready chain based on the designated scheduling
criteria at the time it enters the ready state. Thus, when the processor
is free, the first task on the ready chain is allocated the processor.
- A more efficient method is to schedule the task by placing it in the proper
place on the ready chain based on the designated scheduling criteria at the
time it enters the ready state. Thus, when the processor is free, the first
task on the ready chain is allocated the processor.
- Another mechanism is to maintain a list of FIFOs per priority.
When a task is readied, it is placed on the rear of the FIFO for its
priority. This method is often used with a bitmap to assist in locating
which FIFOs have ready tasks on them.
- Another mechanism is to maintain a list of FIFOs per priority. When a task
is readied, it is placed on the rear of the FIFO for its priority. This
method is often used with a bitmap to assist in locating which FIFOs have
ready tasks on them.
RTEMS currently includes multiple priority based scheduling algorithms
as well as other algorithms which incorporate deadline. Each algorithm
is discussed in the following sections.
RTEMS currently includes multiple priority based scheduling algorithms as well
as other algorithms which incorporate deadline. Each algorithm is discussed in
the following sections.
Deterministic Priority Scheduler
--------------------------------
This is the scheduler implementation which has always been in RTEMS.
After the 4.10 release series, it was factored into pluggable scheduler
selection. It schedules tasks using a priority based algorithm which
takes into account preemption. It is implemented using an array of FIFOs
with a FIFO per priority. It maintains a bitmap which is used to track
which priorities have ready tasks.
This is the scheduler implementation which has always been in RTEMS. After the
4.10 release series, it was factored into pluggable scheduler selection. It
schedules tasks using a priority based algorithm which takes into account
preemption. It is implemented using an array of FIFOs with a FIFO per
priority. It maintains a bitmap which is used to track which priorities have
ready tasks.
This algorithm is deterministic (e.g. predictable and fixed) in execution
time. This comes at the cost of using slightly over three (3) kilobytes
of RAM on a system configured to support 256 priority levels.
This algorithm is deterministic (e.g. predictable and fixed) in execution time.
This comes at the cost of using slightly over three (3) kilobytes of RAM on a
system configured to support 256 priority levels.
This scheduler is only aware of a single core.
@ -110,94 +113,92 @@ Simple Priority Scheduler
-------------------------
This scheduler implementation has the same behaviour as the Deterministic
Priority Scheduler but uses only one linked list to manage all ready
tasks. When a task is readied, a linear search of that linked list is
performed to determine where to insert the newly readied task.
Priority Scheduler but uses only one linked list to manage all ready tasks.
When a task is readied, a linear search of that linked list is performed to
determine where to insert the newly readied task.
This algorithm uses much less RAM than the Deterministic Priority
Scheduler but is *O(n)* where *n* is the number of ready tasks.
In a small system with a small number of tasks, this will not be a
performance issue. Reducing RAM consumption is often critical in small
systems which are incapable of supporting a large number of tasks.
This algorithm uses much less RAM than the Deterministic Priority Scheduler but
is *O(n)* where *n* is the number of ready tasks. In a small system with a
small number of tasks, this will not be a performance issue. Reducing RAM
consumption is often critical in small systems which are incapable of
supporting a large number of tasks.
This scheduler is only aware of a single core.
Simple SMP Priority Scheduler
-----------------------------
This scheduler is based upon the Simple Priority Scheduler and is designed
to have the same behaviour on a single core system. But this scheduler
is capable of scheduling threads across multiple cores in an SMP system.
When given a choice of replacing one of two threads at equal priority
on different cores, this algorithm favors replacing threads which are
preemptible and have executed the longest.
This scheduler is based upon the Simple Priority Scheduler and is designed to
have the same behaviour on a single core system. But this scheduler is capable
of scheduling threads across multiple cores in an SMP system. When given a
choice of replacing one of two threads at equal priority on different cores,
this algorithm favors replacing threads which are preemptible and have executed
the longest.
This algorithm is non-deterministic. When scheduling, it must consider
which tasks are to be executed on each core while avoiding superfluous
task migrations.
This algorithm is non-deterministic. When scheduling, it must consider which
tasks are to be executed on each core while avoiding superfluous task
migrations.
Earliest Deadline First Scheduler
---------------------------------
.. index:: earliest deadline first scheduling
This is an alternative scheduler in RTEMS for single core applications.
The primary EDF advantage is high total CPU utilization (theoretically
up to 100%). It assumes that tasks have priorities equal to deadlines.
This is an alternative scheduler in RTEMS for single core applications. The
primary EDF advantage is high total CPU utilization (theoretically up to
100%). It assumes that tasks have priorities equal to deadlines.
This EDF is initially preemptive, however, individual tasks may be declared
not-preemptive. Deadlines are declared using only Rate Monotonic manager which
goal is to handle periodic behavior. Period is always equal to deadline. All
ready tasks reside in a single ready queue implemented using a red-black tree.
This implementation of EDF schedules two different types of task
priority types while each task may switch between the two types within
its execution. If a task does have a deadline declared using the Rate
Monotonic manager, the task is deadline-driven and its priority is equal
to deadline. On the contrary if a task does not have any deadline or
the deadline is cancelled using the Rate Monotonic manager, the task is
considered a background task with priority equal to that assigned
upon initialization in the same manner as for priority scheduler. Each
background task is of a lower importance than each deadline-driven one
and is scheduled when no deadline-driven task and no higher priority
background task is ready to run.
This implementation of EDF schedules two different types of task priority types
while each task may switch between the two types within its execution. If a
task does have a deadline declared using the Rate Monotonic manager, the task
is deadline-driven and its priority is equal to deadline. On the contrary if a
task does not have any deadline or the deadline is cancelled using the Rate
Monotonic manager, the task is considered a background task with priority equal
to that assigned upon initialization in the same manner as for priority
scheduler. Each background task is of a lower importance than each
deadline-driven one and is scheduled when no deadline-driven task and no higher
priority background task is ready to run.
Every deadline-driven scheduling algorithm requires means for tasks
to claim a deadline. The Rate Monotonic Manager is responsible for
handling periodic execution. In RTEMS periods are equal to deadlines,
thus if a task announces a period, it has to be finished until the
end of this period. The call of ``rtems_rate_monotonic_period``
passes the scheduler the length of oncoming deadline. Moreover, the``rtems_rate_monotonic_cancel`` and ``rtems_rate_monotonic_delete``
calls clear the deadlines assigned to the task.
Every deadline-driven scheduling algorithm requires means for tasks to claim a
deadline. The Rate Monotonic Manager is responsible for handling periodic
execution. In RTEMS periods are equal to deadlines, thus if a task announces a
period, it has to be finished until the end of this period. The call of
``rtems_rate_monotonic_period`` passes the scheduler the length of oncoming
deadline. Moreover, the ``rtems_rate_monotonic_cancel`` and
``rtems_rate_monotonic_delete`` calls clear the deadlines assigned to the task.
Constant Bandwidth Server Scheduling (CBS)
------------------------------------------
.. index:: constant bandwidth server scheduling
This is an alternative scheduler in RTEMS for single core applications.
The CBS is a budget aware extension of EDF scheduler. The main goal of this
This is an alternative scheduler in RTEMS for single core applications. The
CBS is a budget aware extension of EDF scheduler. The main goal of this
scheduler is to ensure temporal isolation of tasks meaning that a task's
execution in terms of meeting deadlines must not be influenced by other
tasks as if they were run on multiple independent processors.
execution in terms of meeting deadlines must not be influenced by other tasks
as if they were run on multiple independent processors.
Each task can be assigned a server (current implementation supports only
one task per server). The server is characterized by period (deadline)
and computation time (budget). The ratio budget/period yields bandwidth,
which is the fraction of CPU to be reserved by the scheduler for each
subsequent period.
Each task can be assigned a server (current implementation supports only one
task per server). The server is characterized by period (deadline) and
computation time (budget). The ratio budget/period yields bandwidth, which is
the fraction of CPU to be reserved by the scheduler for each subsequent period.
The CBS is equipped with a set of rules applied to tasks attached to servers
ensuring that deadline miss because of another task cannot occur.
In case a task breaks one of the rules, its priority is pulled to background
until the end of its period and then restored again. The rules are:
ensuring that deadline miss because of another task cannot occur. In case a
task breaks one of the rules, its priority is pulled to background until the
end of its period and then restored again. The rules are:
- Task cannot exceed its registered budget,
- Task cannot be
unblocked when a ratio between remaining budget and remaining deadline
is higher than declared bandwidth.
- Task cannot be unblocked when a ratio between remaining budget and remaining
deadline is higher than declared bandwidth.
The CBS provides an extensive API. Unlike EDF, the``rtems_rate_monotonic_period`` does not declare a deadline because
it is carried out using CBS API. This call only announces next period.
The CBS provides an extensive API. Unlike EDF, the
``rtems_rate_monotonic_period`` does not declare a deadline because it is
carried out using CBS API. This call only announces next period.
Scheduling Modification Mechanisms
==================================
@ -215,268 +216,249 @@ scheduling decisions:
- manual round-robin selection
Each of these methods provides a powerful capability to customize sets
of tasks to satisfy the unique and particular requirements encountered
in custom real-time applications. Although each mechanism operates
independently, there is a precedence relationship which governs the
effects of scheduling modifications. The evaluation order for scheduling
characteristics is always priority, preemption mode, and timeslicing.
When reading the descriptions of timeslicing and manual round-robin
it is important to keep in mind that preemption (if enabled) of a task
by higher priority tasks will occur as required, overriding the other
factors presented in the description.
Each of these methods provides a powerful capability to customize sets of tasks
to satisfy the unique and particular requirements encountered in custom
real-time applications. Although each mechanism operates independently, there
is a precedence relationship which governs the effects of scheduling
modifications. The evaluation order for scheduling characteristics is always
priority, preemption mode, and timeslicing. When reading the descriptions of
timeslicing and manual round-robin it is important to keep in mind that
preemption (if enabled) of a task by higher priority tasks will occur as
required, overriding the other factors presented in the description.
Task Priority and Scheduling
----------------------------
.. index:: task priority
The most significant task scheduling modification mechanism is the ability
for the user to assign a priority level to each individual task when it
is created and to alter a task's priority at run-time. RTEMS supports
up to 255 priority levels. Level 255 is the lowest priority and level
1 is the highest.
The most significant task scheduling modification mechanism is the ability for
the user to assign a priority level to each individual task when it is created
and to alter a task's priority at run-time. RTEMS supports up to 255 priority
levels. Level 255 is the lowest priority and level 1 is the highest.
Preemption
----------.. index:: preemption
----------
.. index:: preemption
Another way the user can alter the basic scheduling algorithm is by
manipulating the preemption mode flag (``RTEMS_PREEMPT_MASK``)
of individual tasks. If preemption is disabled for a task
(``RTEMS_NO_PREEMPT``), then the task will not relinquish
control of the processor until it terminates, blocks, or re-enables
preemption. Even tasks which become ready to run and possess higher
priority levels will not be allowed to execute. Note that the preemption
setting has no effect on the manner in which a task is scheduled.
manipulating the preemption mode flag (``RTEMS_PREEMPT_MASK``) of individual
tasks. If preemption is disabled for a task (``RTEMS_NO_PREEMPT``), then the
task will not relinquish control of the processor until it terminates, blocks,
or re-enables preemption. Even tasks which become ready to run and possess
higher priority levels will not be allowed to execute. Note that the
preemption setting has no effect on the manner in which a task is scheduled.
It only applies once a task has control of the processor.
Timeslicing
-----------.. index:: timeslicing
-----------
.. index:: timeslicing
.. index:: round robin scheduling
Timeslicing or round-robin scheduling is an additional method which
can be used to alter the basic scheduling algorithm. Like preemption,
timeslicing is specified on a task by task basis using the timeslicing
mode flag (``RTEMS_TIMESLICE_MASK``). If timeslicing is
enabled for a task (``RTEMS_TIMESLICE``), then RTEMS will
limit the amount of time the task can execute before the processor is
allocated to another task. Each tick of the real-time clock reduces
the currently running task's timeslice. When the execution time equals
the timeslice, RTEMS will dispatch another task of the same priority
to execute. If there are no other tasks of the same priority ready to
execute, then the current task is allocated an additional timeslice and
continues to run. Remember that a higher priority task will preempt
the task (unless preemption is disabled) as soon as it is ready to run,
even if the task has not used up its entire timeslice.
Timeslicing or round-robin scheduling is an additional method which can be used
to alter the basic scheduling algorithm. Like preemption, timeslicing is
specified on a task by task basis using the timeslicing mode flag
(``RTEMS_TIMESLICE_MASK``). If timeslicing is enabled for a task
(``RTEMS_TIMESLICE``), then RTEMS will limit the amount of time the task can
execute before the processor is allocated to another task. Each tick of the
real-time clock reduces the currently running task's timeslice. When the
execution time equals the timeslice, RTEMS will dispatch another task of the
same priority to execute. If there are no other tasks of the same priority
ready to execute, then the current task is allocated an additional timeslice
and continues to run. Remember that a higher priority task will preempt the
task (unless preemption is disabled) as soon as it is ready to run, even if the
task has not used up its entire timeslice.
Manual Round-Robin
------------------.. index:: manual round robin
------------------
.. index:: manual round robin
The final mechanism for altering the RTEMS scheduling algorithm is
called manual round-robin. Manual round-robin is invoked by using the``rtems_task_wake_after`` directive with a time interval
of ``RTEMS_YIELD_PROCESSOR``. This allows a task to give
up the processor and be immediately returned to the ready chain at the
end of its priority group. If no other tasks of the same priority are
ready to run, then the task does not lose control of the processor.
The final mechanism for altering the RTEMS scheduling algorithm is called
manual round-robin. Manual round-robin is invoked by using
the ``rtems_task_wake_after`` directive with a time interval of
``RTEMS_YIELD_PROCESSOR``. This allows a task to give up the processor and be
immediately returned to the ready chain at the end of its priority group. If
no other tasks of the same priority are ready to run, then the task does not
lose control of the processor.
Dispatching Tasks
=================.. index:: dispatching
=================
.. index:: dispatching
The dispatcher is the RTEMS component responsible for
allocating the processor to a ready task. In order to allocate
the processor to one task, it must be deallocated or retrieved
from the task currently using it. This involves a concept
called a context switch. To perform a context switch, the
dispatcher saves the context of the current task and restores
the context of the task which has been allocated to the
processor. Saving and restoring a task's context is the
storing/loading of all the essential information about a task to
enable it to continue execution without any effects of the
interruption. For example, the contents of a task's register
set must be the same when it is given the processor as they were
when it was taken away. All of the information that must be
saved or restored for a context switch is located either in the
TCB or on the task's stacks.
The dispatcher is the RTEMS component responsible for allocating the processor
to a ready task. In order to allocate the processor to one task, it must be
deallocated or retrieved from the task currently using it. This involves a
concept called a context switch. To perform a context switch, the dispatcher
saves the context of the current task and restores the context of the task
which has been allocated to the processor. Saving and restoring a task's
context is the storing/loading of all the essential information about a task to
enable it to continue execution without any effects of the interruption. For
example, the contents of a task's register set must be the same when it is
given the processor as they were when it was taken away. All of the
information that must be saved or restored for a context switch is located
either in the TCB or on the task's stacks.
Tasks that utilize a numeric coprocessor and are created with the``RTEMS_FLOATING_POINT`` attribute require additional
operations during a context switch. These additional operations
are necessary to save and restore the floating point context of``RTEMS_FLOATING_POINT`` tasks. To avoid unnecessary save
and restore operations, the state of the numeric coprocessor is only
saved when a ``RTEMS_FLOATING_POINT`` task is dispatched
and that task was not the last task to utilize the coprocessor.
Tasks that utilize a numeric coprocessor and are created with the
``RTEMS_FLOATING_POINT`` attribute require additional operations during a
context switch. These additional operations are necessary to save and restore
the floating point context of ``RTEMS_FLOATING_POINT`` tasks. To avoid
unnecessary save and restore operations, the state of the numeric coprocessor
is only saved when a ``RTEMS_FLOATING_POINT`` task is dispatched and that task
was not the last task to utilize the coprocessor.
Task State Transitions
======================.. index:: task state transitions
======================
.. index:: task state transitions
Tasks in an RTEMS system must always be in one of the
five allowable task states. These states are: executing, ready,
blocked, dormant, and non-existent.
Tasks in an RTEMS system must always be in one of the five allowable task
states. These states are: executing, ready, blocked, dormant, and
non-existent.
A task occupies the non-existent state before
a ``rtems_task_create`` has been issued on its behalf.
A task enters the non-existent state from any other state in the system
when it is deleted with the ``rtems_task_delete`` directive.
While a task occupies this state it does not have a TCB or a task ID
assigned to it; therefore, no other tasks in the system may reference
this task.
A task occupies the non-existent state before a ``rtems_task_create`` has been
issued on its behalf. A task enters the non-existent state from any other
state in the system when it is deleted with the ``rtems_task_delete``
directive. While a task occupies this state it does not have a TCB or a task
ID assigned to it; therefore, no other tasks in the system may reference this
task.
When a task is created via the ``rtems_task_create``
directive it enters the dormant state. This state is not entered through
any other means. Although the task exists in the system, it cannot
actively compete for system resources. It will remain in the dormant
state until it is started via the ``rtems_task_start``
directive, at which time it enters the ready state. The task is now
permitted to be scheduled for the processor and to compete for other
system resources.
When a task is created via the ``rtems_task_create`` directive it enters the
dormant state. This state is not entered through any other means. Although
the task exists in the system, it cannot actively compete for system resources.
It will remain in the dormant state until it is started via the
``rtems_task_start`` directive, at which time it enters the ready state. The
task is now permitted to be scheduled for the processor and to compete for
other system resources.
.. code:: c
.. COMMENT: .. code:: c
.. COMMENT:
.. COMMENT: +-------------------------------------------------------------+
.. COMMENT: | Non-existent |
.. COMMENT: | +-------------------------------------------------------+ |
.. COMMENT: | | | |
.. COMMENT: | | | |
.. COMMENT: | | Creating +---------+ Deleting | |
.. COMMENT: | | -------------------> | Dormant | -------------------> | |
.. COMMENT: | | +---------+ | |
.. COMMENT: | | | | |
.. COMMENT: | | Starting | | |
.. COMMENT: | | | | |
.. COMMENT: | | V Deleting | |
.. COMMENT: | | +-------> +-------+ -------------------> | |
.. COMMENT: | | Yielding / +----- | Ready | ------+ | |
.. COMMENT: | | / / +-------+ <--+ \\ | |
.. COMMENT: | | / / \\ \\ Blocking | |
.. COMMENT: | | / / Dispatching Readying \\ \\ | |
.. COMMENT: | | / V \\ V | |
.. COMMENT: | | +-----------+ Blocking +---------+ | |
.. COMMENT: | | | Executing | --------------> | Blocked | | |
.. COMMENT: | | +-----------+ +---------+ | |
.. COMMENT: | | | |
.. COMMENT: | | | |
.. COMMENT: | +-------------------------------------------------------+ |
.. COMMENT: | Non-existent |
.. COMMENT: +-------------------------------------------------------------+
+-------------------------------------------------------------+
| Non-existent |
| +-------------------------------------------------------+ |
| | | |
| | | |
| | Creating +---------+ Deleting | |
| | -------------------> | Dormant | -------------------> | |
| | +---------+ | |
| | | | |
| | Starting | | |
| | | | |
| | V Deleting | |
| | +-------> +-------+ -------------------> | |
| | Yielding / +----- | Ready | ------+ | |
| | / / +-------+ <--+ \\ | |
| | / / \\ \\ Blocking | |
| | / / Dispatching Readying \\ \\ | |
| | / V \\ V | |
| | +-----------+ Blocking +---------+ | |
| | | Executing | --------------> | Blocked | | |
| | +-----------+ +---------+ | |
| | | |
| | | |
| +-------------------------------------------------------+ |
| Non-existent |
+-------------------------------------------------------------+
.. figure:: states.png
:width: 70%
:align: center
:alt: Task State Transitions
A task occupies the blocked state whenever it is unable to be scheduled
to run. A running task may block itself or be blocked by other tasks in
the system. The running task blocks itself through voluntary operations
that cause the task to wait. The only way a task can block a task other
than itself is with the ``rtems_task_suspend`` directive.
A task enters the blocked state due to any of the following conditions:
A task occupies the blocked state whenever it is unable to be scheduled to run.
A running task may block itself or be blocked by other tasks in the system.
The running task blocks itself through voluntary operations that cause the task
to wait. The only way a task can block a task other than itself is with the
``rtems_task_suspend`` directive. A task enters the blocked state due to any
of the following conditions:
- A task issues a ``rtems_task_suspend`` directive
which blocks either itself or another task in the system.
- A task issues a ``rtems_task_suspend`` directive which blocks either itself
or another task in the system.
- The running task issues a ``rtems_barrier_wait``
directive.
- The running task issues a ``rtems_barrier_wait`` directive.
- The running task issues a ``rtems_message_queue_receive``
directive with the wait option and the message queue is empty.
- The running task issues a ``rtems_message_queue_receive`` directive with the
wait option and the message queue is empty.
- The running task issues an ``rtems_event_receive``
directive with the wait option and the currently pending events do not
satisfy the request.
- The running task issues an ``rtems_event_receive`` directive with the wait
option and the currently pending events do not satisfy the request.
- The running task issues a ``rtems_semaphore_obtain``
directive with the wait option and the requested semaphore is unavailable.
- The running task issues a ``rtems_semaphore_obtain`` directive with the wait
option and the requested semaphore is unavailable.
- The running task issues a ``rtems_task_wake_after``
directive which blocks the task for the given time interval. If the time
interval specified is zero, the task yields the processor and remains
in the ready state.
- The running task issues a ``rtems_task_wake_after`` directive which blocks
the task for the given time interval. If the time interval specified is
zero, the task yields the processor and remains in the ready state.
- The running task issues a ``rtems_task_wake_when``
directive which blocks the task until the requested date and time arrives.
- The running task issues a ``rtems_task_wake_when`` directive which blocks the
task until the requested date and time arrives.
- The running task issues a ``rtems_rate_monotonic_period``
directive and must wait for the specified rate monotonic period
to conclude.
- The running task issues a ``rtems_rate_monotonic_period`` directive and must
wait for the specified rate monotonic period to conclude.
- The running task issues a ``rtems_region_get_segment``
directive with the wait option and there is not an available segment large
enough to satisfy the task's request.
- The running task issues a ``rtems_region_get_segment`` directive with the
wait option and there is not an available segment large enough to satisfy the
task's request.
A blocked task may also be suspended. Therefore, both the suspension
and the blocking condition must be removed before the task becomes ready
to run again.
A blocked task may also be suspended. Therefore, both the suspension and the
blocking condition must be removed before the task becomes ready to run again.
A task occupies the ready state when it is able to be scheduled to run,
but currently does not have control of the processor. Tasks of the same
or higher priority will yield the processor by either becoming blocked,
completing their timeslice, or being deleted. All tasks with the same
priority will execute in FIFO order. A task enters the ready state due
to any of the following conditions:
A task occupies the ready state when it is able to be scheduled to run, but
currently does not have control of the processor. Tasks of the same or higher
priority will yield the processor by either becoming blocked, completing their
timeslice, or being deleted. All tasks with the same priority will execute in
FIFO order. A task enters the ready state due to any of the following
conditions:
- A running task issues a ``rtems_task_resume``
directive for a task that is suspended and the task is not blocked
waiting on any resource.
- A running task issues a ``rtems_task_resume`` directive for a task that is
suspended and the task is not blocked waiting on any resource.
- A running task issues a ``rtems_message_queue_send``,``rtems_message_queue_broadcast``, or a``rtems_message_queue_urgent`` directive
which posts a message to the queue on which the blocked task is
- A running task issues a ``rtems_message_queue_send``,
``rtems_message_queue_broadcast``, or a ``rtems_message_queue_urgent``
directive which posts a message to the queue on which the blocked task is
waiting.
- A running task issues an ``rtems_event_send``
directive which sends an event condition to a task which is blocked
waiting on that event condition.
- A running task issues an ``rtems_event_send`` directive which sends an event
condition to a task which is blocked waiting on that event condition.
- A running task issues a ``rtems_semaphore_release``
directive which releases the semaphore on which the blocked task is
waiting.
- A running task issues a ``rtems_semaphore_release`` directive which releases
the semaphore on which the blocked task is waiting.
- A timeout interval expires for a task which was blocked
by a call to the ``rtems_task_wake_after`` directive.
- A timeout interval expires for a task which was blocked by a call to the
``rtems_task_wake_after`` directive.
- A timeout period expires for a task which blocked by a
call to the ``rtems_task_wake_when`` directive.
- A timeout period expires for a task which blocked by a call to the
``rtems_task_wake_when`` directive.
- A running task issues a ``rtems_region_return_segment``
directive which releases a segment to the region on which the blocked task
is waiting and a resulting segment is large enough to satisfy
the task's request.
- A running task issues a ``rtems_region_return_segment`` directive which
releases a segment to the region on which the blocked task is waiting and a
resulting segment is large enough to satisfy the task's request.
- A rate monotonic period expires for a task which blocked
by a call to the ``rtems_rate_monotonic_period`` directive.
- A rate monotonic period expires for a task which blocked by a call to the
``rtems_rate_monotonic_period`` directive.
- A timeout interval expires for a task which was blocked
waiting on a message, event, semaphore, or segment with a
timeout specified.
- A timeout interval expires for a task which was blocked waiting on a message,
event, semaphore, or segment with a timeout specified.
- A running task issues a directive which deletes a
message queue, a semaphore, or a region on which the blocked
task is waiting.
- A running task issues a directive which deletes a message queue, a semaphore,
or a region on which the blocked task is waiting.
- A running task issues a ``rtems_task_restart``
directive for the blocked task.
- A running task issues a ``rtems_task_restart`` directive for the blocked
task.
- The running task, with its preemption mode enabled, may
be made ready by issuing any of the directives that may unblock
a task with a higher priority. This directive may be issued
from the running task itself or from an ISR.
A ready task occupies the executing state when it has
control of the CPU. A task enters the executing state due to
any of the following conditions:
- The running task, with its preemption mode enabled, may be made ready by
issuing any of the directives that may unblock a task with a higher priority.
This directive may be issued from the running task itself or from an ISR. A
ready task occupies the executing state when it has control of the CPU. A
task enters the executing state due to any of the following conditions:
- The task is the highest priority ready task in the
system.
- The task is the highest priority ready task in the system.
- The running task blocks and the task is next in the
scheduling queue. The task may be of equal priority as in
round-robin scheduling or the task may possess the highest
priority of the remaining ready tasks.
- The running task blocks and the task is next in the scheduling queue. The
task may be of equal priority as in round-robin scheduling or the task may
possess the highest priority of the remaining ready tasks.
- The running task may reenable its preemption mode and a
task exists in the ready queue that has a higher priority than
the running task.
- The running task may reenable its preemption mode and a task exists in the
ready queue that has a higher priority than the running task.
- The running task lowers its own priority and another
task is of higher priority as a result.
- The running task raises the priority of a task above its
own and the running task is in preemption mode.
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
- The running task lowers its own priority and another task is of higher
priority as a result.
- The running task raises the priority of a task above its own and the running
task is in preemption mode.

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@ -1,3 +1,7 @@
.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
Timer Manager
#############
@ -9,25 +13,25 @@ Introduction
The timer manager provides support for timer
facilities. The directives provided by the timer manager are:
- ``rtems_timer_create`` - Create a timer
- rtems_timer_create_ - Create a timer
- ``rtems_timer_ident`` - Get ID of a timer
- rtems_timer_ident_ - Get ID of a timer
- ``rtems_timer_cancel`` - Cancel a timer
- rtems_timer_cancel_ - Cancel a timer
- ``rtems_timer_delete`` - Delete a timer
- rtems_timer_delete_ - Delete a timer
- ``rtems_timer_fire_after`` - Fire timer after interval
- rtems_timer_fire_after_ - Fire timer after interval
- ``rtems_timer_fire_when`` - Fire timer when specified
- rtems_timer_fire_when_ - Fire timer when specified
- ``rtems_timer_initiate_server`` - Initiate server for task-based timers
- rtems_timer_initiate_server_ - Initiate server for task-based timers
- ``rtems_timer_server_fire_after`` - Fire task-based timer after interval
- rtems_timer_server_fire_after_ - Fire task-based timer after interval
- ``rtems_timer_server_fire_when`` - Fire task-based timer when specified
- rtems_timer_server_fire_when_ - Fire task-based timer when specified
- ``rtems_timer_reset`` - Reset an interval timer
- rtems_timer_reset_ - Reset an interval timer
Background
==========
@ -40,65 +44,60 @@ A clock tick is required to support the functionality provided by this manager.
Timers
------
A timer is an RTEMS object which allows the
application to schedule operations to occur at specific times in
the future. User supplied timer service routines are invoked by
either the ``rtems_clock_tick`` directive or
a special Timer Server task when the timer fires. Timer service
routines may perform any operations or directives which normally
would be performed by the application code which invoked the``rtems_clock_tick`` directive.
A timer is an RTEMS object which allows the application to schedule operations
to occur at specific times in the future. User supplied timer service routines
are invoked by either the ``rtems_clock_tick`` directive or a special Timer
Server task when the timer fires. Timer service routines may perform any
operations or directives which normally would be performed by the application
code which invoked the ``rtems_clock_tick`` directive.
The timer can be used to implement watchdog routines
which only fire to denote that an application error has
occurred. The timer is reset at specific points in the
application to ensure that the watchdog does not fire. Thus, if
the application does not reset the watchdog timer, then the
timer service routine will fire to indicate that the application
has failed to reach a reset point. This use of a timer is
sometimes referred to as a "keep alive" or a "deadman" timer.
The timer can be used to implement watchdog routines which only fire to denote
that an application error has occurred. The timer is reset at specific points
in the application to ensure that the watchdog does not fire. Thus, if the
application does not reset the watchdog timer, then the timer service routine
will fire to indicate that the application has failed to reach a reset point.
This use of a timer is sometimes referred to as a "keep alive" or a "deadman"
timer.
Timer Server
------------
The Timer Server task is responsible for executing the timer
service routines associated with all task-based timers.
This task executes at a priority higher than any RTEMS application
task, and is created non-preemptible, and thus can be viewed logically as
the lowest priority interrupt.
The Timer Server task is responsible for executing the timer service routines
associated with all task-based timers. This task executes at a priority higher
than any RTEMS application task, and is created non-preemptible, and thus can
be viewed logically as the lowest priority interrupt.
By providing a mechanism where timer service routines execute
in task rather than interrupt space, the application is
allowed a bit more flexibility in what operations a timer
service routine can perform. For example, the Timer Server
can be configured to have a floating point context in which case
it would be safe to perform floating point operations
from a task-based timer. Most of the time, executing floating
point instructions from an interrupt service routine
is not considered safe. However, since the Timer Server task
is non-preemptible, only directives allowed from an ISR can be
called in the timer service routine.
By providing a mechanism where timer service routines execute in task rather
than interrupt space, the application is allowed a bit more flexibility in what
operations a timer service routine can perform. For example, the Timer Server
can be configured to have a floating point context in which case it would be
safe to perform floating point operations from a task-based timer. Most of the
time, executing floating point instructions from an interrupt service routine
is not considered safe. However, since the Timer Server task is
non-preemptible, only directives allowed from an ISR can be called in the timer
service routine.
The Timer Server is designed to remain blocked until a
task-based timer fires. This reduces the execution overhead
of the Timer Server.
The Timer Server is designed to remain blocked until a task-based timer fires.
This reduces the execution overhead of the Timer Server.
Timer Service Routines
----------------------
The timer service routine should adhere to C calling
conventions and have a prototype similar to the following:.. index:: rtems_timer_service_routine
The timer service routine should adhere to C calling conventions and have a
prototype similar to the following:
.. index:: rtems_timer_service_routine
.. code:: c
rtems_timer_service_routine user_routine(
rtems_id timer_id,
void \*user_data
rtems_id timer_id,
void *user_data
);
Where the timer_id parameter is the RTEMS object ID
of the timer which is being fired and user_data is a pointer to
user-defined information which may be utilized by the timer
service routine. The argument user_data may be NULL.
Where the timer_id parameter is the RTEMS object ID of the timer which is being
fired and user_data is a pointer to user-defined information which may be
utilized by the timer service routine. The argument user_data may be NULL.
Operations
==========
@ -106,95 +105,89 @@ Operations
Creating a Timer
----------------
The ``rtems_timer_create`` directive creates a timer by
allocating a Timer Control Block (TMCB), assigning the timer a
user-specified name, and assigning it a timer ID. Newly created
timers do not have a timer service routine associated with them
and are not active.
The ``rtems_timer_create`` directive creates a timer by allocating a Timer
Control Block (TMCB), assigning the timer a user-specified name, and assigning
it a timer ID. Newly created timers do not have a timer service routine
associated with them and are not active.
Obtaining Timer IDs
-------------------
When a timer is created, RTEMS generates a unique
timer ID and assigns it to the created timer until it is
deleted. The timer ID may be obtained by either of two methods.
First, as the result of an invocation of the``rtems_timer_create``
directive, the timer ID is stored in a user provided location.
Second, the timer ID may be obtained later using the``rtems_timer_ident`` directive. The timer ID
is used by other directives to manipulate this timer.
When a timer is created, RTEMS generates a unique timer ID and assigns it to
the created timer until it is deleted. The timer ID may be obtained by either
of two methods. First, as the result of an invocation of the
``rtems_timer_create`` directive, the timer ID is stored in a user provided
location. Second, the timer ID may be obtained later using the
``rtems_timer_ident`` directive. The timer ID is used by other directives to
manipulate this timer.
Initiating an Interval Timer
----------------------------
The ``rtems_timer_fire_after``
and ``rtems_timer_server_fire_after``
directives initiate a timer to fire a user provided
timer service routine after the specified
number of clock ticks have elapsed. When the interval has
elapsed, the timer service routine will be invoked from the``rtems_clock_tick`` directive if it was initiated
by the ``rtems_timer_fire_after`` directive
and from the Timer Server task if initiated by the``rtems_timer_server_fire_after`` directive.
The ``rtems_timer_fire_after`` and ``rtems_timer_server_fire_after`` directives
initiate a timer to fire a user provided timer service routine after the
specified number of clock ticks have elapsed. When the interval has elapsed,
the timer service routine will be invoked from the ``rtems_clock_tick``
directive if it was initiated by the ``rtems_timer_fire_after`` directive and
from the Timer Server task if initiated by the
``rtems_timer_server_fire_after`` directive.
Initiating a Time of Day Timer
------------------------------
The ``rtems_timer_fire_when``
and ``rtems_timer_server_fire_when``
directive initiate a timer to
fire a user provided timer service routine when the specified
time of day has been reached. When the interval has elapsed,
the timer service routine will be invoked from the``rtems_clock_tick`` directive
by the ``rtems_timer_fire_when`` directive
and from the Timer Server task if initiated by the``rtems_timer_server_fire_when`` directive.
The ``rtems_timer_fire_when`` and ``rtems_timer_server_fire_when`` directive
initiate a timer to fire a user provided timer service routine when the
specified time of day has been reached. When the interval has elapsed, the
timer service routine will be invoked from the ``rtems_clock_tick`` directive
by the ``rtems_timer_fire_when`` directive and from the Timer Server task if
initiated by the ``rtems_timer_server_fire_when`` directive.
Canceling a Timer
-----------------
The ``rtems_timer_cancel`` directive is used to halt the
specified timer. Once canceled, the timer service routine will
not fire unless the timer is reinitiated. The timer can be
reinitiated using the ``rtems_timer_reset``,``rtems_timer_fire_after``, and``rtems_timer_fire_when`` directives.
The ``rtems_timer_cancel`` directive is used to halt the specified timer. Once
canceled, the timer service routine will not fire unless the timer is
reinitiated. The timer can be reinitiated using the ``rtems_timer_reset``,
``rtems_timer_fire_after``, and ``rtems_timer_fire_when`` directives.
Resetting a Timer
-----------------
The ``rtems_timer_reset`` directive is used to restore an
interval timer initiated by a previous invocation of``rtems_timer_fire_after`` or``rtems_timer_server_fire_after`` to
its original interval length. If the
timer has not been used or the last usage of this timer
was by the ``rtems_timer_fire_when``
or ``rtems_timer_server_fire_when``
directive, then an error is returned. The timer service routine
is not changed or fired by this directive.
The ``rtems_timer_reset`` directive is used to restore an interval timer
initiated by a previous invocation of ``rtems_timer_fire_after`` or
``rtems_timer_server_fire_after`` to its original interval length. If the
timer has not been used or the last usage of this timer was by the
``rtems_timer_fire_when`` or ``rtems_timer_server_fire_when`` directive, then
an error is returned. The timer service routine is not changed or fired by
this directive.
Initiating the Timer Server
---------------------------
The ``rtems_timer_initiate_server`` directive is used to
allocate and start the execution of the Timer Server task. The
application can specify both the stack size and attributes of the
Timer Server. The Timer Server executes at a priority higher than
any application task and thus the user can expect to be preempted
as the result of executing the ``rtems_timer_initiate_server``
The ``rtems_timer_initiate_server`` directive is used to allocate and start the
execution of the Timer Server task. The application can specify both the stack
size and attributes of the Timer Server. The Timer Server executes at a
priority higher than any application task and thus the user can expect to be
preempted as the result of executing the ``rtems_timer_initiate_server``
directive.
Deleting a Timer
----------------
The ``rtems_timer_delete`` directive is used to delete a timer.
If the timer is running and has not expired, the timer is
automatically canceled. The timer's control block is returned
to the TMCB free list when it is deleted. A timer can be
deleted by a task other than the task which created the timer.
The ``rtems_timer_delete`` directive is used to delete a timer. If the timer
is running and has not expired, the timer is automatically canceled. The
timer's control block is returned to the TMCB free list when it is deleted. A
timer can be deleted by a task other than the task which created the timer.
Any subsequent references to the timer's name and ID are invalid.
Directives
==========
This section details the timer manager's directives.
A subsection is dedicated to each of this manager's directives
and describes the calling sequence, related constants, usage,
and status codes.
This section details the timer manager's directives. A subsection is dedicated
to each of this manager's directives and describes the calling sequence,
related constants, usage, and status codes.
.. _rtems_timer_create:
TIMER_CREATE - Create a timer
-----------------------------
@ -207,29 +200,36 @@ TIMER_CREATE - Create a timer
.. code:: c
rtems_status_code rtems_timer_create(
rtems_name name,
rtems_id \*id
rtems_name name,
rtems_id *id
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - timer created successfully
``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL
``RTEMS_INVALID_NAME`` - invalid timer name
``RTEMS_TOO_MANY`` - too many timers created
``RTEMS_SUCCESSFUL``
timer created successfully
``RTEMS_INVALID_ADDRESS``
``id`` is NULL
``RTEMS_INVALID_NAME``
invalid timer name
``RTEMS_TOO_MANY``
too many timers created
**DESCRIPTION:**
This directive creates a timer. The assigned timer
id is returned in id. This id is used to access the timer with
other timer manager directives. For control and maintenance of
the timer, RTEMS allocates a TMCB from the local TMCB free pool
and initializes it.
This directive creates a timer. The assigned timer id is returned in id. This
id is used to access the timer with other timer manager directives. For
control and maintenance of the timer, RTEMS allocates a TMCB from the local
TMCB free pool and initializes it.
**NOTES:**
This directive will not cause the calling task to be
preempted.
This directive will not cause the calling task to be preempted.
.. _rtems_timer_ident:
TIMER_IDENT - Get ID of a timer
-------------------------------
@ -242,29 +242,34 @@ TIMER_IDENT - Get ID of a timer
.. code:: c
rtems_status_code rtems_timer_ident(
rtems_name name,
rtems_id \*id
rtems_name name,
rtems_id *id
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - timer identified successfully
``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL
``RTEMS_INVALID_NAME`` - timer name not found
``RTEMS_SUCCESSFUL``
timer identified successfully
``RTEMS_INVALID_ADDRESS``
``id`` is NULL
``RTEMS_INVALID_NAME``
timer name not found
**DESCRIPTION:**
This directive obtains the timer id associated with
the timer name to be acquired. If the timer name is not unique,
then the timer id will match one of the timers with that name.
However, this timer id is not guaranteed to correspond to the
desired timer. The timer id is used to access this timer in
This directive obtains the timer id associated with the timer name to be
acquired. If the timer name is not unique, then the timer id will match one of
the timers with that name. However, this timer id is not guaranteed to
correspond to the desired timer. The timer id is used to access this timer in
other timer related directives.
**NOTES:**
This directive will not cause the running task to be
preempted.
This directive will not cause the running task to be preempted.
.. _rtems_timer_cancel:
TIMER_CANCEL - Cancel a timer
-----------------------------
@ -277,23 +282,29 @@ TIMER_CANCEL - Cancel a timer
.. code:: c
rtems_status_code rtems_timer_cancel(
rtems_id id
rtems_id id
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - timer canceled successfully
``RTEMS_INVALID_ID`` - invalid timer id
``RTEMS_SUCCESSFUL``
timer canceled successfully
``RTEMS_INVALID_ID``
invalid timer id
**DESCRIPTION:**
This directive cancels the timer id. This timer will
be reinitiated by the next invocation of ``rtems_timer_reset``,``rtems_timer_fire_after``, or``rtems_timer_fire_when`` with this id.
This directive cancels the timer id. This timer will be reinitiated by the
next invocation of ``rtems_timer_reset``, ``rtems_timer_fire_after``, or
``rtems_timer_fire_when`` with this id.
**NOTES:**
This directive will not cause the running task to be preempted.
.. _rtems_timer_delete:
TIMER_DELETE - Delete a timer
-----------------------------
.. index:: delete a timer
@ -305,27 +316,30 @@ TIMER_DELETE - Delete a timer
.. code:: c
rtems_status_code rtems_timer_delete(
rtems_id id
rtems_id id
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - timer deleted successfully
``RTEMS_INVALID_ID`` - invalid timer id
``RTEMS_SUCCESSFUL``
timer deleted successfully
``RTEMS_INVALID_ID``
invalid timer id
**DESCRIPTION:**
This directive deletes the timer specified by id. If
the timer is running, it is automatically canceled. The TMCB
for the deleted timer is reclaimed by RTEMS.
This directive deletes the timer specified by id. If the timer is running, it
is automatically canceled. The TMCB for the deleted timer is reclaimed by
RTEMS.
**NOTES:**
This directive will not cause the running task to be
preempted.
This directive will not cause the running task to be preempted.
A timer can be deleted by a task other than the task
which created the timer.
A timer can be deleted by a task other than the task which created the timer.
.. _rtems_timer_fire_after:
TIMER_FIRE_AFTER - Fire timer after interval
--------------------------------------------
@ -338,32 +352,38 @@ TIMER_FIRE_AFTER - Fire timer after interval
.. code:: c
rtems_status_code rtems_timer_fire_after(
rtems_id id,
rtems_interval ticks,
rtems_timer_service_routine_entry routine,
void \*user_data
rtems_id id,
rtems_interval ticks,
rtems_timer_service_routine_entry routine,
void *user_data
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - timer initiated successfully
``RTEMS_INVALID_ADDRESS`` - ``routine`` is NULL
``RTEMS_INVALID_ID`` - invalid timer id
``RTEMS_INVALID_NUMBER`` - invalid interval
``RTEMS_SUCCESSFUL``
timer initiated successfully
``RTEMS_INVALID_ADDRESS``
``routine`` is NULL
``RTEMS_INVALID_ID``
invalid timer id
``RTEMS_INVALID_NUMBER``
invalid interval
**DESCRIPTION:**
This directive initiates the timer specified by id.
If the timer is running, it is automatically canceled before
being initiated. The timer is scheduled to fire after an
interval ticks clock ticks has passed. When the timer fires,
the timer service routine routine will be invoked with the
argument user_data.
This directive initiates the timer specified by id. If the timer is running,
it is automatically canceled before being initiated. The timer is scheduled to
fire after an interval ticks clock ticks has passed. When the timer fires, the
timer service routine routine will be invoked with the argument user_data.
**NOTES:**
This directive will not cause the running task to be
preempted.
This directive will not cause the running task to be preempted.
.. _rtems_timer_fire_when:
TIMER_FIRE_WHEN - Fire timer when specified
-------------------------------------------
@ -376,34 +396,44 @@ TIMER_FIRE_WHEN - Fire timer when specified
.. code:: c
rtems_status_code rtems_timer_fire_when(
rtems_id id,
rtems_time_of_day \*wall_time,
rtems_timer_service_routine_entry routine,
void \*user_data
rtems_id id,
rtems_time_of_day *wall_time,
rtems_timer_service_routine_entry routine,
void *user_data
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - timer initiated successfully
``RTEMS_INVALID_ADDRESS`` - ``routine`` is NULL
``RTEMS_INVALID_ADDRESS`` - ``wall_time`` is NULL
``RTEMS_INVALID_ID`` - invalid timer id
``RTEMS_NOT_DEFINED`` - system date and time is not set
``RTEMS_INVALID_CLOCK`` - invalid time of day
``RTEMS_SUCCESSFUL``
timer initiated successfully
``RTEMS_INVALID_ADDRESS``
``routine`` is NULL
``RTEMS_INVALID_ADDRESS``
``wall_time`` is NULL
``RTEMS_INVALID_ID``
invalid timer id
``RTEMS_NOT_DEFINED``
system date and time is not set
``RTEMS_INVALID_CLOCK``
invalid time of day
**DESCRIPTION:**
This directive initiates the timer specified by id.
If the timer is running, it is automatically canceled before
being initiated. The timer is scheduled to fire at the time of
day specified by wall_time. When the timer fires, the timer
service routine routine will be invoked with the argument
user_data.
This directive initiates the timer specified by id. If the timer is running,
it is automatically canceled before being initiated. The timer is scheduled to
fire at the time of day specified by wall_time. When the timer fires, the
timer service routine routine will be invoked with the argument user_data.
**NOTES:**
This directive will not cause the running task to be
preempted.
This directive will not cause the running task to be preempted.
.. _rtems_timer_initiate_server:
TIMER_INITIATE_SERVER - Initiate server for task-based timers
-------------------------------------------------------------
@ -416,32 +446,38 @@ TIMER_INITIATE_SERVER - Initiate server for task-based timers
.. code:: c
rtems_status_code rtems_timer_initiate_server(
uint32_t priority,
uint32_t stack_size,
rtems_attribute attribute_set
uint32_t priority,
uint32_t stack_size,
rtems_attribute attribute_set
)
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - Timer Server initiated successfully
``RTEMS_TOO_MANY`` - too many tasks created
``RTEMS_SUCCESSFUL``
Timer Server initiated successfully
``RTEMS_TOO_MANY``
too many tasks created
**DESCRIPTION:**
This directive initiates the Timer Server task. This task
is responsible for executing all timers initiated via the``rtems_timer_server_fire_after`` or``rtems_timer_server_fire_when`` directives.
This directive initiates the Timer Server task. This task is responsible for
executing all timers initiated via the ``rtems_timer_server_fire_after`` or
``rtems_timer_server_fire_when`` directives.
**NOTES:**
This directive could cause the calling task to be preempted.
The Timer Server task is created using the``rtems_task_create`` service and must be accounted
for when configuring the system.
The Timer Server task is created using the ``rtems_task_create`` service and
must be accounted for when configuring the system.
Even through this directive invokes the ``rtems_task_create``
and ``rtems_task_start`` directives, it should only fail
due to resource allocation problems.
Even through this directive invokes the ``rtems_task_create`` and
``rtems_task_start`` directives, it should only fail due to resource allocation
problems.
.. _rtems_timer_server_fire_after:
TIMER_SERVER_FIRE_AFTER - Fire task-based timer after interval
--------------------------------------------------------------
@ -454,35 +490,44 @@ TIMER_SERVER_FIRE_AFTER - Fire task-based timer after interval
.. code:: c
rtems_status_code rtems_timer_server_fire_after(
rtems_id id,
rtems_interval ticks,
rtems_timer_service_routine_entry routine,
void \*user_data
rtems_id id,
rtems_interval ticks,
rtems_timer_service_routine_entry routine,
void *user_data
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - timer initiated successfully
``RTEMS_INVALID_ADDRESS`` - ``routine`` is NULL
``RTEMS_INVALID_ID`` - invalid timer id
``RTEMS_INVALID_NUMBER`` - invalid interval
``RTEMS_INCORRECT_STATE`` - Timer Server not initiated
``RTEMS_SUCCESSFUL``
timer initiated successfully
``RTEMS_INVALID_ADDRESS``
``routine`` is NULL
``RTEMS_INVALID_ID``
invalid timer id
``RTEMS_INVALID_NUMBER``
invalid interval
``RTEMS_INCORRECT_STATE``
Timer Server not initiated
**DESCRIPTION:**
This directive initiates the timer specified by id and specifies
that when it fires it will be executed by the Timer Server.
This directive initiates the timer specified by id and specifies that when it
fires it will be executed by the Timer Server.
If the timer is running, it is automatically canceled before
being initiated. The timer is scheduled to fire after an
interval ticks clock ticks has passed. When the timer fires,
the timer service routine routine will be invoked with the
argument user_data.
If the timer is running, it is automatically canceled before being initiated.
The timer is scheduled to fire after an interval ticks clock ticks has passed.
When the timer fires, the timer service routine routine will be invoked with
the argument user_data.
**NOTES:**
This directive will not cause the running task to be
preempted.
This directive will not cause the running task to be preempted.
.. _rtems_timer_server_fire_when:
TIMER_SERVER_FIRE_WHEN - Fire task-based timer when specified
-------------------------------------------------------------
@ -495,37 +540,50 @@ TIMER_SERVER_FIRE_WHEN - Fire task-based timer when specified
.. code:: c
rtems_status_code rtems_timer_server_fire_when(
rtems_id id,
rtems_time_of_day \*wall_time,
rtems_timer_service_routine_entry routine,
void \*user_data
rtems_id id,
rtems_time_of_day *wall_time,
rtems_timer_service_routine_entry routine,
void *user_data
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - timer initiated successfully
``RTEMS_INVALID_ADDRESS`` - ``routine`` is NULL
``RTEMS_INVALID_ADDRESS`` - ``wall_time`` is NULL
``RTEMS_INVALID_ID`` - invalid timer id
``RTEMS_NOT_DEFINED`` - system date and time is not set
``RTEMS_INVALID_CLOCK`` - invalid time of day
``RTEMS_INCORRECT_STATE`` - Timer Server not initiated
``RTEMS_SUCCESSFUL``
timer initiated successfully
``RTEMS_INVALID_ADDRESS``
``routine`` is NULL
``RTEMS_INVALID_ADDRESS``
``wall_time`` is NULL
``RTEMS_INVALID_ID``
invalid timer id
``RTEMS_NOT_DEFINED``
system date and time is not set
``RTEMS_INVALID_CLOCK``
invalid time of day
``RTEMS_INCORRECT_STATE``
Timer Server not initiated
**DESCRIPTION:**
This directive initiates the timer specified by id and specifies
that when it fires it will be executed by the Timer Server.
This directive initiates the timer specified by id and specifies that when it
fires it will be executed by the Timer Server.
If the timer is running, it is automatically canceled before
being initiated. The timer is scheduled to fire at the time of
day specified by wall_time. When the timer fires, the timer
service routine routine will be invoked with the argument
user_data.
If the timer is running, it is automatically canceled before being initiated.
The timer is scheduled to fire at the time of day specified by wall_time. When
the timer fires, the timer service routine routine will be invoked with the
argument user_data.
**NOTES:**
This directive will not cause the running task to be
preempted.
This directive will not cause the running task to be preempted.
.. _rtems_timer_reset:
TIMER_RESET - Reset an interval timer
-------------------------------------
@ -538,45 +596,36 @@ TIMER_RESET - Reset an interval timer
.. code:: c
rtems_status_code rtems_timer_reset(
rtems_id id
rtems_id id
);
**DIRECTIVE STATUS CODES:**
``RTEMS_SUCCESSFUL`` - timer reset successfully
``RTEMS_INVALID_ID`` - invalid timer id
``RTEMS_NOT_DEFINED`` - attempted to reset a when or newly created timer
``RTEMS_SUCCESSFUL``
timer reset successfully
``RTEMS_INVALID_ID``
invalid timer id
``RTEMS_NOT_DEFINED``
attempted to reset a when or newly created timer
**DESCRIPTION:**
This directive resets the timer associated with id.
This timer must have been previously initiated with either the``rtems_timer_fire_after`` or``rtems_timer_server_fire_after``
directive. If active the timer is canceled,
after which the timer is reinitiated using the same interval and
timer service routine which the original``rtems_timer_fire_after````rtems_timer_server_fire_after``
directive used.
This directive resets the timer associated with id. This timer must have been
previously initiated with either the ``rtems_timer_fire_after`` or
``rtems_timer_server_fire_after`` directive. If active the timer is canceled,
after which the timer is reinitiated using the same interval and timer service
routine which the original ``rtems_timer_fire_after`` or
``rtems_timer_server_fire_after`` directive used.
**NOTES:**
If the timer has not been used or the last usage of this timer
was by a ``rtems_timer_fire_when`` or``rtems_timer_server_fire_when``
directive, then the ``RTEMS_NOT_DEFINED`` error is
returned.
If the timer has not been used or the last usage of this timer was by a
``rtems_timer_fire_when`` or ``rtems_timer_server_fire_when`` directive, then
the ``RTEMS_NOT_DEFINED`` error is returned.
Restarting a cancelled after timer results in the timer being
reinitiated with its previous timer service routine and interval.
Restarting a cancelled after timer results in the timer being reinitiated with
its previous timer service routine and interval.
This directive will not cause the running task to be preempted.
.. COMMENT: COPYRIGHT (c) 1988-2013.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
.. COMMENT: Open Issues
.. COMMENT: - nicen up the tables
.. COMMENT: - use math mode to print formulas