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Diffstat (limited to 'c-user/key_concepts.rst')
| -rw-r--r-- | c-user/key_concepts.rst | 44 |
1 files changed, 8 insertions, 36 deletions
diff --git a/c-user/key_concepts.rst b/c-user/key_concepts.rst index f717a87..25f9249 100644 --- a/c-user/key_concepts.rst +++ b/c-user/key_concepts.rst @@ -94,19 +94,14 @@ name: Object IDs ---------- -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 -~~~~~~~~~~~~~~~~~~~~~~~~~~~ +An object ID is a unique 32-bit 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 some +RTEMS services. + +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 @@ -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 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 --------------------- |