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author | Sebastian Huber <sebastian.huber@embedded-brains.de> | 2020-08-20 10:06:42 +0200 |
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committer | Sebastian Huber <sebastian.huber@embedded-brains.de> | 2020-09-02 17:57:10 +0200 |
commit | aebb6fd7c7abd598d803ca0b8013e2761633f03a (patch) | |
tree | f03ca76d0b69ac932b19fd779d6b2afe065aa9cd /c-user/region_manager.rst | |
parent | c-user: Split up rate-monotonic manager (diff) | |
download | rtems-docs-aebb6fd7c7abd598d803ca0b8013e2761633f03a.tar.bz2 |
c-user: Split up region manager
This makes it easier to automatically generate parts of the manager
documentation in the future.
Update #3993.
Diffstat (limited to '')
-rw-r--r-- | c-user/region/directives.rst (renamed from c-user/region_manager.rst) | 213 |
1 files changed, 0 insertions, 213 deletions
diff --git a/c-user/region_manager.rst b/c-user/region/directives.rst index f9cfb46..be994f6 100644 --- a/c-user/region_manager.rst +++ b/c-user/region/directives.rst @@ -2,219 +2,6 @@ .. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR) -.. index:: regions - -Region Manager -************** - -Introduction -============ - -The region manager provides facilities to dynamically allocate memory in -variable sized units. The directives provided by the region manager are: - -- rtems_region_create_ - Create a region - -- rtems_region_ident_ - Get ID of a region - -- rtems_region_delete_ - Delete a region - -- rtems_region_extend_ - Add memory to a region - -- rtems_region_get_segment_ - Get segment from a region - -- rtems_region_return_segment_ - Return segment to a region - -- rtems_region_get_segment_size_ - Obtain size of a segment - -- rtems_region_resize_segment_ - Change size of a segment - -- rtems_region_get_information_ - Get region information - -- rtems_region_get_free_information_ - Get region free information - -Background -========== - -.. index:: region, definition -.. index:: segment, definition - -Region Manager Definitions --------------------------- - -A region makes up a physically contiguous memory space with user-defined -boundaries from which variable-sized segments are dynamically allocated and -deallocated. A segment is a variable size section of memory which is allocated -in multiples of a user-defined page size. This page size is required to be a -multiple of four greater than or equal to four. For example, if a request for -a 350-byte segment is made in a region with 256-byte pages, then a 512-byte -segment is allocated. - -Regions are organized as doubly linked chains of variable sized memory blocks. -Memory requests are allocated using a first-fit algorithm. If available, the -requester receives the number of bytes requested (rounded up to the next page -size). RTEMS requires some overhead from the region's memory for each segment -that is allocated. Therefore, an application should only modify the memory of -a segment that has been obtained from the region. The application should NOT -modify the memory outside of any obtained segments and within the region's -boundaries while the region is currently active in the system. - -Upon return to the region, the free block is coalesced with its neighbors (if -free) on both sides to produce the largest possible unused block. - -.. index:: region attribute set, building - -Building an Attribute Set -------------------------- - -In general, an attribute set is built by a bitwise OR of the desired attribute -components. The set of valid region attributes is provided in the following -table: - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_FIFO`` - - tasks wait by FIFO (default) - * - ``RTEMS_PRIORITY`` - - tasks wait by priority - -Attribute values are specifically designed to be mutually exclusive, therefore -bitwise OR and addition operations are equivalent as long as each attribute -appears exactly once in the component list. An attribute listed as a default -is not required to appear in the attribute list, although it is a good -programming practice to specify default attributes. If all defaults are -desired, the attribute ``RTEMS_DEFAULT_ATTRIBUTES`` should be specified on this -call. - -This example demonstrates the attribute_set parameter needed to create a region -with the task priority waiting queue discipline. The attribute_set parameter -to the ``rtems_region_create`` directive should be ``RTEMS_PRIORITY``. - -Building an Option Set ----------------------- - -In general, an option is built by a bitwise OR of the desired option -components. The set of valid options for the ``rtems_region_get_segment`` -directive are listed in the following table: - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_WAIT`` - - task will wait for segment (default) - * - ``RTEMS_NO_WAIT`` - - task should not wait - -Option values are specifically designed to be mutually exclusive, therefore -bitwise OR and addition operations are equivalent as long as each option -appears exactly once in the component list. An option listed as a default is -not required to appear in the option list, although it is a good programming -practice to specify default options. If all defaults are desired, the -option ``RTEMS_DEFAULT_OPTIONS`` should be specified on this call. - -This example demonstrates the option parameter needed to poll for a segment. -The option parameter passed to the ``rtems_region_get_segment`` directive -should be ``RTEMS_NO_WAIT``. - -Operations -========== - -Creating a Region ------------------ - -The ``rtems_region_create`` directive creates a region with the user-defined -name. The user may select FIFO or task priority as the method for placing -waiting tasks in the task wait queue. RTEMS allocates a Region Control Block -(RNCB) from the RNCB free list to maintain the newly created region. RTEMS -also generates a unique region ID which is returned to the calling task. - -It is not possible to calculate the exact number of bytes available to the user -since RTEMS requires overhead for each segment allocated. For example, a -region with one segment that is the size of the entire region has more -available bytes than a region with two segments that collectively are the size -of the entire region. This is because the region with one segment requires -only the overhead for one segment, while the other region requires the overhead -for two segments. - -Due to automatic coalescing, the number of segments in the region dynamically -changes. Therefore, the total overhead required by RTEMS dynamically changes. - -Obtaining Region IDs --------------------- - -When a region is created, RTEMS generates a unique region ID and assigns it to -the created region until it is deleted. The region ID may be obtained by -either of two methods. First, as the result of an invocation of the -``rtems_region_create`` directive, the region ID is stored in a user provided -location. Second, the region ID may be obtained later using the -``rtems_region_ident`` directive. The region ID is used by other region -manager directives to access this region. - -Adding Memory to a Region -------------------------- - -The ``rtems_region_extend`` directive may be used to add memory to an existing -region. The caller specifies the size in bytes and starting address of the -memory being added. - -Acquiring a Segment -------------------- - -The ``rtems_region_get_segment`` directive attempts to acquire a segment from a -specified region. If the region has enough available free memory, then a -segment is returned successfully to the caller. When the segment cannot be -allocated, one of the following situations applies: - -- By default, the calling task will wait forever to acquire the segment. - -- Specifying the ``RTEMS_NO_WAIT`` option forces an immediate return with an - error status code. - -- Specifying a timeout limits the interval the task will wait before returning - with an error status code. - -If the task waits for the segment, then it is placed in the region's task wait -queue in either FIFO or task priority order. All tasks waiting on a region are -returned an error when the message queue is deleted. - -Releasing a Segment -------------------- - -When a segment is returned to a region by the ``rtems_region_return_segment`` -directive, it is merged with its unallocated neighbors to form the largest -possible segment. The first task on the wait queue is examined to determine if -its segment request can now be satisfied. If so, it is given a segment and -unblocked. This process is repeated until the first task's segment request -cannot be satisfied. - -Obtaining the Size of a Segment -------------------------------- - -The ``rtems_region_get_segment_size`` directive returns the size in bytes of -the specified segment. The size returned includes any "extra" memory included -in the segment because of rounding up to a page size boundary. - -Changing the Size of a Segment ------------------------------- - -The ``rtems_region_resize_segment`` directive is used to change the size in -bytes of the specified segment. The size may be increased or decreased. When -increasing the size of a segment, it is possible that the request cannot be -satisfied. This directive provides functionality similar to the ``realloc()`` -function in the Standard C Library. - -Deleting a Region ------------------ - -A region can be removed from the system and returned to RTEMS with the -``rtems_region_delete`` directive. When a region is deleted, its control block -is returned to the RNCB free list. A region with segments still allocated is -not allowed to be deleted. Any task attempting to do so will be returned an -error. As a result of this directive, all tasks blocked waiting to obtain a -segment from the region will be readied and returned a status code which -indicates that the region was deleted. - Directives ========== |