18.4. Directives¶

This section details the directives of the Region Manager. A subsection is dedicated to each of this manager’s directives and lists the calling sequence, parameters, description, return values, and notes of the directive.

18.4.1. rtems_region_create()¶

Creates a region.

CALLING SEQUENCE:

rtems_status_code rtems_region_create(
  rtems_name      name,
  void           *starting_address,
  uintptr_t       length,
  uintptr_t       page_size,
  rtems_attribute attribute_set,
  rtems_id       *id
);

PARAMETERS:

name: This parameter is the object name of the region.
starting_address: This parameter is the starting address of the memory area managed by the region.
length: This parameter is the length in bytes of the memory area managed by the region.
page_size: This parameter is the alignment of the starting address and length of each allocated segment of the region.
attribute_set: This parameter is the attribute set of the region.
id: This parameter is the pointer to an rtems_id object. When the directive call is successful, the identifier of the created region will be stored in this object.

DESCRIPTION:

This directive creates a region which resides on the local node. The region has the user-defined object name specified in name. The assigned object identifier is returned in id. This identifier is used to access the region with other region related directives.

The region manages the contiguous memory area which starts at starting_address and is length bytes long. The memory area shall be large enough to contain some internal region administration data.

The starting address and length of segments allocated from the region will be an integral multiple of page_size. The specified page size will be aligned to an implementation-dependent minimum alignment if necessary.

The attribute set specified in attribute_set is built through a bitwise or of the attribute constants described below. Not all combinations of attributes are allowed. Some attributes are mutually exclusive. If mutually exclusive attributes are combined, the behaviour is undefined. Attributes not mentioned below are not evaluated by this directive and have no effect. Default attributes can be selected by using the RTEMS_DEFAULT_ATTRIBUTES constant.

The task wait queue discipline is selected by the mutually exclusive RTEMS_FIFO and RTEMS_PRIORITY attributes. The discipline defines the order in which tasks wait for allocatable segments on a currently empty region.

The FIFO discipline is the default and can be emphasized through use of the RTEMS_FIFO attribute.
The priority discipline is selected by the RTEMS_PRIORITY attribute.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_NAME: The name parameter was invalid.
RTEMS_INVALID_ADDRESS: The id parameter was NULL.
RTEMS_INVALID_ADDRESS: The starting_address parameter was NULL.
RTEMS_TOO_MANY: There was no inactive object available to create a region. The number of regions available to the application is configured through the CONFIGURE_MAXIMUM_REGIONS application configuration option.
RTEMS_INVALID_SIZE: The page_size parameter was invalid.
RTEMS_INVALID_SIZE: The memory area specified in starting_address and length was too small.

NOTES:

For control and maintenance of the region, RTEMS allocates a RNCB from the local RNCB free pool and initializes it.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.
The number of regions available to the application is configured through the CONFIGURE_MAXIMUM_REGIONS application configuration option.
Where the object class corresponding to the directive is configured to use unlimited objects, the directive may allocate memory from the RTEMS Workspace.

18.4.2. rtems_region_ident()¶

Identifies a region by the object name.

CALLING SEQUENCE:

rtems_status_code rtems_region_ident( rtems_name name, rtems_id *id );

PARAMETERS:

name: This parameter is the object name to look up.
id: This parameter is the pointer to an rtems_id object. When the directive call is successful, the object identifier of an object with the specified name will be stored in this object.

DESCRIPTION:

This directive obtains a region identifier associated with the region name specified in name.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The id parameter was NULL.
RTEMS_INVALID_NAME: The name parameter was 0.
RTEMS_INVALID_NAME: There was no object with the specified name on the local node.

NOTES:

If the region name is not unique, then the region identifier will match the first region with that name in the search order. However, this region identifier is not guaranteed to correspond to the desired region.

The objects are searched from lowest to the highest index. Only the local node is searched.

The region identifier is used with other region related directives to access the region.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within any runtime context.
The directive will not cause the calling task to be preempted.

18.4.3. rtems_region_delete()¶

Deletes the region.

CALLING SEQUENCE:

rtems_status_code rtems_region_delete( rtems_id id );

PARAMETERS:

id: This parameter is the region identifier.

DESCRIPTION:

This directive deletes the region specified by id.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ID: There was no region associated with the identifier specified by id.
RTEMS_RESOURCE_IN_USE: There were segments of the region still in use.

NOTES:

The region cannot be deleted if any of its segments are still allocated.

The RNCB for the deleted region is reclaimed by RTEMS.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.
The calling task does not have to be the task that created the object. Any local task that knows the object identifier can delete the object.
Where the object class corresponding to the directive is configured to use unlimited objects, the directive may free memory to the RTEMS Workspace.

18.4.4. rtems_region_extend()¶

Extends the region.

CALLING SEQUENCE:

rtems_status_code rtems_region_extend(
  rtems_id  id,
  void     *starting_address,
  uintptr_t length
);

PARAMETERS:

id: This parameter is the region identifier.
starting_address: This parameter is the starting address of the memory area to extend the region.
length: This parameter is the length in bytes of the memory area to extend the region.

DESCRIPTION:

This directive adds the memory area which starts at starting_address for length bytes to the region specified by id.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The starting_address parameter was NULL.
RTEMS_INVALID_ID: There was no region associated with the identifier specified by id.
RTEMS_INVALID_ADDRESS: The memory area specified by starting_address and length was insufficient to extend the heap.

NOTES:

There are no alignment requirements for the memory area. The memory area must be big enough to contain some maintenance blocks. It must not overlap parts of the current heap memory areas. Disconnected memory areas added to the heap will lead to used blocks which cover the gaps. Extending with an inappropriate memory area will corrupt the heap resulting in undefined behaviour.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.

18.4.5. rtems_region_get_segment()¶

Gets a segment from the region.

CALLING SEQUENCE:

rtems_status_code rtems_region_get_segment(
  rtems_id       id,
  uintptr_t      size,
  rtems_option   option_set,
  rtems_interval timeout,
  void         **segment
);

PARAMETERS:

id: This parameter is the region identifier.
size: This parameter is the size in bytes of the segment to allocate.
option_set: This parameter is the option set.
timeout: This parameter is the timeout in clock ticks if the RTEMS_WAIT option is set. Use RTEMS_NO_TIMEOUT to wait potentially forever.
segment: This parameter is the pointer to a void pointer object. When the directive call is successful, the begin address of the allocated segment will be stored in this object.

DESCRIPTION:

This directive gets a segment from the region specified by id.

The option set specified in option_set is built through a bitwise or of the option constants described below. Not all combinations of options are allowed. Some options are mutually exclusive. If mutually exclusive options are combined, the behaviour is undefined. Options not mentioned below are not evaluated by this directive and have no effect. Default options can be selected by using the RTEMS_DEFAULT_OPTIONS constant.

The calling task can wait or try to get a segment from the region according to the mutually exclusive RTEMS_WAIT and RTEMS_NO_WAIT options.

Waiting to get a segment from the region is the default and can be emphasized through the use of the RTEMS_WAIT option. The timeout parameter defines how long the calling task is willing to wait. Use RTEMS_NO_TIMEOUT to wait potentially forever, otherwise set a timeout interval in clock ticks.
Trying to get a segment from the region is selected by the RTEMS_NO_WAIT option. If this option is defined, then the timeout parameter is ignored. When a segment from the region cannot be immediately allocated, then the RTEMS_UNSATISFIED status is returned.

With either RTEMS_WAIT or RTEMS_NO_WAIT if there is a segment of the requested size is available, then it is returned in segment and this directive returns immediately with the RTEMS_SUCCESSFUL status code.

If the calling task chooses to return immediately and the region has no segment of the requested size available, then the directive returns immediately with the RTEMS_UNSATISFIED status code. If the calling task chooses to wait for a segment, then the calling task is placed on the region wait queue and blocked. If the region was created with the RTEMS_PRIORITY option specified, then the calling task is inserted into the wait queue according to its priority. But, if the region was created with the RTEMS_FIFO option specified, then the calling task is placed at the rear of the wait queue.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The segment parameter was NULL.
RTEMS_INVALID_SIZE: The size parameter was zero.
RTEMS_INVALID_ID: There was no region associated with the identifier specified by id.
RTEMS_INVALID_SIZE: The size parameter exceeded the maximum segment size which is possible for the region.
RTEMS_UNSATISFIED: The region had no segment of the requested size immediately available.
RTEMS_TIMEOUT: The timeout happened while the calling task was waiting to get a segment from the region.

NOTES:

The actual length of the allocated segment may be larger than the requested size because a segment size is always a multiple of the region’s page size.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.
When the request cannot be immediately satisfied and the RTEMS_WAIT option is set, the calling task blocks at some point during the directive call.
The timeout functionality of the directive requires a clock tick.

18.4.6. rtems_region_return_segment()¶

Returns the segment to the region.

CALLING SEQUENCE:

rtems_status_code rtems_region_return_segment( rtems_id id, void *segment );

PARAMETERS:

id: This parameter is the region identifier.
segment: This parameter is the begin address of the segment to return.

DESCRIPTION:

This directive returns the segment specified by segment to the region specified by id. The returned segment is merged with its 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.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ID: There was no region associated with the identifier specified by id.
RTEMS_INVALID_ADDRESS: The segment was not within the region.

NOTES:

This directive will cause the calling task to be preempted if one or more local tasks are waiting for a segment and the following conditions exist:

A waiting task has a higher priority than the calling task.
The size of the segment required by the waiting task is less than or equal to the size of the segment returned.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may unblock a task. This may cause the calling task to be preempted.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.

18.4.7. rtems_region_resize_segment()¶

Changes the size of the segment.

CALLING SEQUENCE:

rtems_status_code rtems_region_resize_segment(
  rtems_id   id,
  void      *segment,
  uintptr_t  size,
  uintptr_t *old_size
);

PARAMETERS:

id: This parameter is the region identifier.
segment: This parameter is the begin address of the segment to resize.
size: This parameter is the requested new size of the segment.
old_size: This parameter is the pointer to an uintptr_t object. When the directive call is successful, the old size of the segment will be stored in this object.

DESCRIPTION:

This directive is used to increase or decrease the size of the segment of the region specified by id. When increasing the size of a segment, it is possible that there is no memory available contiguous to the segment. In this case, the request is unsatisfied.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The old_size parameter was NULL.
RTEMS_INVALID_ID: There was no region associated with the identifier specified by id.
RTEMS_INVALID_ADDRESS: The segment was not within the region.
RTEMS_UNSATISFIED: The region was unable to resize the segment.

NOTES:

If an attempt to increase the size of a segment fails, then the application may want to allocate a new segment of the desired size, copy the contents of the original segment to the new, larger segment and then return the original segment.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.

18.4.8. rtems_region_get_information()¶

Gets the region information.

CALLING SEQUENCE:

rtems_status_code rtems_region_get_information(
  rtems_id                id,
  Heap_Information_block *the_info
);

PARAMETERS:

id: This parameter is the region identifier.
the_info: This parameter is the pointer to a Heap_Information_block object. When the directive call is successful, the information of the region will be stored in this object.

DESCRIPTION:

This directive is used to obtain information about the used and free memory in the region specified by id. This is a snapshot at the time of the call. The information will be returned in the structure pointed to by the_info.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The the_info parameter was NULL.
RTEMS_INVALID_ID: There was no region associated with the identifier specified by id.

NOTES:

This is primarily intended as a mechanism to obtain a diagnostic information. This method forms am O(n) scan of the free and an O(n) scan of the used blocks in the region to calculate the information provided. Given that the execution time is driven by the number of used and free blocks, it can take a non-deterministic time to execute.

To get only the free information of the region use rtems_region_get_free_information().

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.

18.4.9. rtems_region_get_free_information()¶

Gets the region free information.

CALLING SEQUENCE:

rtems_status_code rtems_region_get_free_information(
  rtems_id                id,
  Heap_Information_block *the_info
);

PARAMETERS:

id: This parameter is the region identifier.
the_info: This parameter is the pointer to a Heap_Information_block object. When the directive call is successful, the free information of the region will be stored in this object.

DESCRIPTION:

This directive is used to obtain information about the free memory in the region specified by id. This is a snapshot at the time of the call. The information will be returned in the structure pointed to by the_info.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The the_info parameter was NULL.
RTEMS_INVALID_ID: There was no region associated with the identifier specified by id.

NOTES:

This directive uses the same structure to return information as the rtems_region_get_information() directive but does not fill in the used information.

This is primarily intended as a mechanism to obtain a diagnostic information. This method forms am O(n) scan of the free in the region to calculate the information provided. Given that the execution time is driven by the number of used and free blocks, it can take a non-deterministic time to execute. Typically, there are many used blocks and a much smaller number of used blocks making a call to this directive less expensive than a call to rtems_region_get_information().

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.

18.4.10. rtems_region_get_segment_size()¶

Gets the size of the region segment.

CALLING SEQUENCE:

rtems_status_code rtems_region_get_segment_size(
  rtems_id   id,
  void      *segment,
  uintptr_t *size
);

PARAMETERS:

id: This parameter is the region identifier.
segment: This parameter is the begin address of the segment.
size: This parameter is the pointer to a uintptr_t object. When the directive call is successful, the size of the segment in bytes will be stored in this object.

DESCRIPTION:

This directive obtains the size in bytes of the segment specified by segment of the region specified by id in size.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The segment parameter was NULL.
RTEMS_INVALID_ADDRESS: The size parameter was NULL.
RTEMS_INVALID_ID: There was no region associated with the identifier specified by id.
RTEMS_INVALID_ADDRESS: The segment was not within the region.

NOTES:

The actual length of the allocated segment may be larger than the requested size because a segment size is always a multiple of the region’s page size.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.