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c-user: Clarify time formats

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Update #4572.
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Sebastian Huber 2021-12-16 08:20:27 +01:00
parent 732d8bca8f
commit 786b89ac86
1 changed files with 26 additions and 11 deletions
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c-user/clock/background.rst
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@ -1,5 +1,6 @@
.. SPDX-License-Identifier: CC-BY-SA-4.0 .. SPDX-License-Identifier: CC-BY-SA-4.0
.. Copyright (C) 2021 embedded brains GmbH (http://www.embedded-brains.de)
.. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR) .. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR)
Background Background
@ -29,7 +30,7 @@ and date format:
.. code-block:: c .. code-block:: c
struct rtems_tod_control { typedef struct {
uint32_t year; /* greater than 1987 */ uint32_t year; /* greater than 1987 */
uint32_t month; /* 1 - 12 */ uint32_t month; /* 1 - 12 */
uint32_t day; /* 1 - 31 */ uint32_t day; /* 1 - 31 */
@ -37,20 +38,34 @@ and date format:
uint32_t minute; /* 0 - 59 */ uint32_t minute; /* 0 - 59 */
uint32_t second; /* 0 - 59 */ uint32_t second; /* 0 - 59 */
uint32_t ticks; /* elapsed between seconds */ uint32_t ticks; /* elapsed between seconds */
}; } rtems_time_of_day;
typedef struct rtems_tod_control rtems_time_of_day;
The native date and time format is the only format supported when setting the 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 system date and time using the :ref:`InterfaceRtemsClockSet` directive. Some
applications expect to operate on a *UNIX-style* date and time data structure. 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 For example, the :ref:`InterfaceRtemsClockGetTodTimeval` returns the date and
``struct timeval`` format. time in ``struct timeval`` format.
The ``struct timeval`` data structure has two fields: ``tv_sec`` and .. index:: struct timeval
``tv_usec`` which are seconds and microseconds, respectively. The ``tv_sec`` .. index:: struct timespec
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, Some directives use data structures defined by :term:`POSIX`. The ``struct
1988*. timeval`` data structure has two members: ``tv_sec`` and ``tv_usec`` which are
seconds and microseconds, respectively. The ``struct timespec`` data structure
has two members: ``tv_sec`` and ``tv_nsec`` which are seconds and nanoseconds,
respectively. For :term:`CLOCK_REALTIME` time points, the ``tv_sec`` member in
these data structures is the number of seconds since the :term:`Unix epoch` but
will never be prior to the :term:`RTEMS epoch`.
.. index:: struct bintime
.. index:: sbintime_t
The ``struct bintime`` and ``sbintime_t`` time formats used by some directives
originate in FreeBSD. The ``struct bintime`` data structure which represents
time in a binary time format has two members: ``sec`` and ``frac`` which are
seconds and fractions of a second in units of :math:`1 / 2^{64}` seconds,
respectively. The ``sbintime_t`` type is a signed 64-bit integer type used to
represent time in units of :math:`1 / 2^{32}` seconds.
.. index:: timeslicing .. index:: timeslicing