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c-user: Remove 16-bit object identifiers

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Close #3603.
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Sebastian Huber 2018-11-16 07:14:37 +01:00
parent fdaef809d5
commit 92745a4baa
1 changed files with 7 additions and 35 deletions
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c-user/key_concepts.rst
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@ -94,19 +94,14 @@ name:
Object IDs Object IDs
---------- ----------
An object ID is a unique unsigned integer value which uniquely identifies an An object ID is a unique 32-bit unsigned integer value which uniquely
object instance. Object IDs are passed as arguments to many directives in identifies an object instance. Object IDs are passed as arguments to many
RTEMS and RTEMS translates the ID to an internal object pointer. The efficient directives in RTEMS and RTEMS translates the ID to an internal object pointer.
manipulation of object IDs is critical to the performance of RTEMS services. The efficient manipulation of object IDs is critical to the performance of some
Because of this, there are two object Id formats defined. Each target RTEMS services.
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 Object ID Format
~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~
The thirty-two bit format for an object ID is composed of four parts: API, 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 class, node, and index. The data type ``rtems_id`` is used to store
@ -129,29 +124,6 @@ sixteen bits form an identifier within a particular object type. This
identifier, called the object index, ranges in value from 1 to the maximum identifier, called the object index, ranges in value from 1 to the maximum
number of objects configured for this object type. 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.
.. code-block:: c
15 11 10 8 7 0
+---------+-------+--------------+
| | | |
| Class | API | Index |
| | | |
+---------+-------+--------------+
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.
Object ID Description Object ID Description
--------------------- ---------------------