7.4. Directives¶

This section details the directives of the Task 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.

7.4.1. rtems_task_create()¶

Creates a task.

CALLING SEQUENCE:

rtems_status_code rtems_task_create(
  rtems_name          name,
  rtems_task_priority initial_priority,
  size_t              stack_size,
  rtems_mode          initial_modes,
  rtems_attribute     attribute_set,
  rtems_id           *id
);

PARAMETERS:

name: This parameter is the object name of the task.
initial_priority: This parameter is the initial task priority.
stack_size: This parameter is the task stack size in bytes.
initial_modes: This parameter is the initial mode set of the task.
attribute_set: This parameter is the attribute set of the task.
id: This parameter is the pointer to an rtems_id object. When the directive call is successful, the identifier of the created task will be stored in this object.

DESCRIPTION:

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

The initial priority of the task is specified in initial_priority. The home scheduler of the created task is the home scheduler of the calling task at some time point during the task creation. The initial task priority specified in initial_priority shall be valid for this scheduler.

The stack size of the task is specified in stack_size. If the requested stack size is less than the configured minimum stack size, then RTEMS will use the configured minimum as the stack size for this task. The configured minimum stack size is defined by the CONFIGURE_MINIMUM_TASK_STACK_SIZE application configuration option. In addition to being able to specify the task stack size as a integer, there are two constants which may be specified:

The RTEMS_MINIMUM_STACK_SIZE constant can be specified to use the recommended minimum stack size for the target processor. This value is selected by the RTEMS maintainers conservatively to minimize the risk of blown stacks for most user applications. Using this constant when specifying the task stack size, indicates that the stack size will be at least RTEMS_MINIMUM_STACK_SIZE bytes in size. If the user configured minimum stack size is larger than the recommended minimum, then it will be used.
The RTEMS_CONFIGURED_MINIMUM_STACK_SIZE constant can be specified to use the minimum stack size that was configured by the application. If not explicitly configured by the application, the default configured minimum stack size is the target processor dependent value RTEMS_MINIMUM_STACK_SIZE. Since this uses the configured minimum stack size value, you may get a stack size that is smaller or larger than the recommended minimum. This can be used to provide large stacks for all tasks on complex applications or small stacks on applications that are trying to conserve memory.

The initial mode set specified in initial_modes is built through a bitwise or of the mode constants described below. Not all combinations of modes are allowed. Some modes are mutually exclusive. If mutually exclusive modes are combined, the behaviour is undefined. Default task modes can be selected by using the RTEMS_DEFAULT_MODES constant. The task mode set defines

the preemption mode of the task: RTEMS_PREEMPT (default) or RTEMS_NO_PREEMPT,
the timeslicing mode of the task: RTEMS_TIMESLICE or RTEMS_NO_TIMESLICE (default),
the ASR processing mode of the task: RTEMS_ASR (default) or RTEMS_NO_ASR,
the interrupt level of the task: RTEMS_INTERRUPT_LEVEL() with a default of RTEMS_INTERRUPT_LEVEL( 0 ) which is associated with enabled interrupts.

The initial preemption mode of the task is enabled or disabled.

An enabled preemption is the default and can be emphasized through the use of the RTEMS_PREEMPT mode constant.
A disabled preemption is set by the RTEMS_NO_PREEMPT mode constant.

The initial timeslicing mode of the task is enabled or disabled.

A disabled timeslicing is the default and can be emphasized through the use of the RTEMS_NO_TIMESLICE mode constant.
An enabled timeslicing is set by the RTEMS_TIMESLICE mode constant.

The initial ASR processing mode of the task is enabled or disabled.

An enabled ASR processing is the default and can be emphasized through the use of the RTEMS_ASR mode constant.
A disabled ASR processing is set by the RTEMS_NO_ASR mode constant.

The initial interrupt level mode of the task is defined by RTEMS_INTERRUPT_LEVEL().

Task execution with interrupts enabled the default and can be emphasized through the use of the RTEMS_INTERRUPT_LEVEL() mode macro with a value of zero (0) for the parameter. An interrupt level of zero is associated with enabled interrupts on all target processors.
Task execution at a non-zero interrupt level can be specified by the RTEMS_INTERRUPT_LEVEL() mode macro with a non-zero value for the parameter. The interrupt level portion of the task mode supports a maximum of 256 interrupt levels. These levels are mapped onto the interrupt levels actually supported by the target processor in a processor dependent fashion.

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 attribute set defines

the scope of the task: RTEMS_LOCAL (default) or RTEMS_GLOBAL and
the floating-point unit use of the task: RTEMS_FLOATING_POINT or RTEMS_NO_FLOATING_POINT (default).

The task has a local or global scope in a multiprocessing network (this attribute does not refer to SMP systems). The scope is selected by the mutually exclusive RTEMS_LOCAL and RTEMS_GLOBAL attributes.

A local scope is the default and can be emphasized through the use of the RTEMS_LOCAL attribute. A local task can be only used by the node which created it.
A global scope is established if the RTEMS_GLOBAL attribute is set. Setting the global attribute in a single node system has no effect.the

The use of the floating-point unit is selected by the mutually exclusive RTEMS_FLOATING_POINT and RTEMS_NO_FLOATING_POINT attributes. On some target processors, the use of the floating-point unit can be enabled or disabled for each task. Other target processors may have no hardware floating-point unit or enable the use of the floating-point unit for all tasks. Consult the RTEMS CPU Architecture Supplement for the details.

A disabled floating-point unit is the default and can be emphasized through use of the RTEMS_NO_FLOATING_POINT attribute. For performance reasons, it is recommended that tasks not using the floating-point unit should specify this attribute.
An enabled floating-point unit is selected by the RTEMS_FLOATING_POINT 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_PRIORITY: The initial_priority was invalid.
RTEMS_TOO_MANY: There was no inactive object available to create a task. The number of tasks available to the application is configured through the CONFIGURE_MAXIMUM_TASKS application configuration option.
RTEMS_TOO_MANY: In multiprocessing configurations, there was no inactive global object available to create a global task. The number of global objects available to the application is configured through the CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS application configuration option.
RTEMS_UNSATISFIED: There was not enough memory to allocate the task storage area. The task storage area contains the task stack, the thread-local storage, and the floating point context.
RTEMS_UNSATISFIED: One of the task create extensions failed to create the task.
RTEMS_UNSATISFIED: In SMP configurations, the non-preemption mode was not supported.
RTEMS_UNSATISFIED: In SMP configurations, the interrupt level mode was not supported.

NOTES:

The task processor affinity is initialized to the set of online processors.

When created, a task is placed in the dormant state and can only be made ready to execute using the directive rtems_task_start().

Application developers should consider the stack usage of the device drivers when calculating the stack size required for tasks which utilize the driver. The task stack size shall account for an target processor dependent interrupt stack frame which may be placed on the stack of the interrupted task while servicing an interrupt. The stack checker may be used to monitor the stack usage, see CONFIGURE_STACK_CHECKER_ENABLED.

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

The TCB for a global task is allocated on the local node. Task should not be made global unless remote tasks must interact with the task. This is to avoid the system overhead incurred by the creation of a global task. When a global task is created, the task’s name and identifier must be transmitted to every node in the system for insertion in the local copy of the global object table.

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 directive operates on a global object, the directive sends a message to remote nodes. This may preempt the calling task.
The number of tasks available to the application is configured through the CONFIGURE_MAXIMUM_TASKS 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.
The number of global objects available to the application is configured through the CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS application configuration option.

7.4.2. rtems_task_construct()¶

Constructs a task from the specified task configuration.

CALLING SEQUENCE:

rtems_status_code rtems_task_construct(
  const rtems_task_config *config,
  rtems_id                *id
);

PARAMETERS:

config: This parameter is the pointer to an rtems_task_config object. It configures the task.
id: This parameter is the pointer to an rtems_id object. When the directive call is successful, the identifier of the constructed task will be stored in this object.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The config parameter was NULL.
RTEMS_INVALID_NAME: The task name was invalid.
RTEMS_INVALID_ADDRESS: The id parameter was NULL.
RTEMS_INVALID_PRIORITY: The initial task priority was invalid.
RTEMS_INVALID_SIZE: The thread-local storage size is greater than the maximum thread-local storage size specified in the task configuration. The thread-local storage size is determined by the thread-local variables used by the application and CONFIGURE_MAXIMUM_THREAD_LOCAL_STORAGE_SIZE.
RTEMS_INVALID_SIZE: The task storage area was too small to provide a task stack of the configured minimum size, see CONFIGURE_MINIMUM_TASK_STACK_SIZE. The task storage area contains the task stack, the thread-local storage, and the floating-point context on architectures with a separate floating-point context.
RTEMS_TOO_MANY: There was no inactive task object available to construct a task.
RTEMS_TOO_MANY: In multiprocessing configurations, there was no inactive global object available to construct a global task.
RTEMS_UNSATISFIED: One of the task create extensions failed during the task construction.
RTEMS_UNSATISFIED: In SMP configurations, the non-preemption mode was not supported.
RTEMS_UNSATISFIED: In SMP configurations, the interrupt level mode was not supported.

NOTES:

In contrast to tasks created by rtems_task_create(), the tasks constructed by this directive use a user-provided task storage area. The task storage area contains the task stack, the thread-local storage, and the floating-point context on architectures with a separate floating-point context.

This directive is intended for applications which do not want to use the RTEMS Workspace and instead statically allocate all operating system resources. It is not recommended to use rtems_task_create() and rtems_task_construct() together in an application. It is also not recommended to use rtems_task_construct() for drivers or general purpose libraries. The reason for these recommendations is that the task configuration needs settings which can be only given with a through knowledge of the application resources.

An application based solely on static allocation can avoid any runtime memory allocators. This can simplify the application architecture as well as any analysis that may be required.

The stack space estimate done by <rtems/confdefs.h> assumes that all tasks are created by rtems_task_create(). The estimate can be adjusted to take user-provided task storage areas into account through the CONFIGURE_MINIMUM_TASKS_WITH_USER_PROVIDED_STORAGE application configuration option.

The CONFIGURE_MAXIMUM_TASKS should include tasks constructed by rtems_task_construct().

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 directive operates on a global object, the directive sends a message to remote nodes. This may preempt the calling task.
The number of tasks available to the application is configured through the CONFIGURE_MAXIMUM_TASKS 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.
The number of global objects available to the application is configured through the CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS application configuration option.

7.4.3. rtems_task_ident()¶

Identifies a task by the object name.

CALLING SEQUENCE:

rtems_status_code rtems_task_ident(
  rtems_name name,
  uint32_t   node,
  rtems_id  *id
);

PARAMETERS:

name: This parameter is the object name to look up.
node: This parameter is the node or node set to search for a matching object.
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 task identifier associated with the task name specified in name.

A task may obtain its own identifier by specifying RTEMS_WHO_AM_I for the name.

The node to search is specified in node. It shall be

a valid node number,
the constant RTEMS_SEARCH_ALL_NODES to search in all nodes,
the constant RTEMS_SEARCH_LOCAL_NODE to search in the local node only, or
the constant RTEMS_SEARCH_OTHER_NODES to search in all nodes except the local node.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The id parameter was NULL.
RTEMS_INVALID_NAME: There was no object with the specified name on the specified nodes.
RTEMS_INVALID_NODE: In multiprocessing configurations, the specified node was invalid.

NOTES:

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

The objects are searched from lowest to the highest index. If node is RTEMS_SEARCH_ALL_NODES, all nodes are searched with the local node being searched first. All other nodes are searched from lowest to the highest node number.

If node is a valid node number which does not represent the local node, then only the tasks exported by the designated node are searched.

This directive does not generate activity on remote nodes. It accesses only the local copy of the global object table.

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

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.

7.4.4. rtems_task_self()¶

Gets the task identifier of the calling task.

CALLING SEQUENCE:

rtems_id rtems_task_self( void );

DESCRIPTION:

This directive returns the task identifier of the calling task.

RETURN VALUES:

Returns the task identifier of the calling task.

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 will not cause the calling task to be preempted.

7.4.5. rtems_task_start()¶

Starts the task.

CALLING SEQUENCE:

rtems_status_code rtems_task_start(
  rtems_id            id,
  rtems_task_entry    entry_point,
  rtems_task_argument argument
);

PARAMETERS:

id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.
entry_point: This parameter is the task entry point.
argument: This parameter is the task entry point argument.

DESCRIPTION:

This directive readies the task, specified by id, for execution based on the priority and execution mode specified when the task was created. The task entry point of the task is given in entry_point. The task’s entry point argument is contained in argument.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The entry_point parameter was NULL.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by id.
RTEMS_INCORRECT_STATE: The task was not in the dormant state.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The task resided on a remote node.

NOTES:

The type of the entry point argument is an unsigned integer type. However, the integer type has the property that any valid pointer to void can be converted to this type and then converted back to a pointer to void. The result will compare equal to the original pointer. The type can represent at least 32 bits. Some applications use the entry point argument as an index into a parameter table to get task-specific parameters.

Any actions performed on a dormant task such as suspension or change of priority are nullified when the task is initiated via the rtems_task_start() directive.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
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.

7.4.6. rtems_task_restart()¶

Restarts the task.

CALLING SEQUENCE:

rtems_status_code rtems_task_restart(
  rtems_id            id,
  rtems_task_argument argument
);

PARAMETERS:

id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.
argument: This parameter is the task entry point argument.

DESCRIPTION:

This directive resets the task specified by id to begin execution at its original entry point. The task’s priority and execution mode are set to the original creation values. If the task is currently blocked, RTEMS automatically makes the task ready. A task can be restarted from any state, except the dormant state. The task’s entry point argument is contained in argument.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by id.
RTEMS_INCORRECT_STATE: The task never started.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The task resided on a remote node.

NOTES:

The type of the entry point argument is an unsigned integer type. However, the integer type has the property that any valid pointer to void can be converted to this type and then converted back to a pointer to void. The result will compare equal to the original pointer. The type can represent at least 32 bits. Some applications use the entry point argument as an index into a parameter table to get task-specific parameters.

A new entry point argument may be used to distinguish between the initial rtems_task_start() of the task and any ensuing calls to rtems_task_restart() of the task. This can be beneficial in deleting a task. Instead of deleting a task using the rtems_task_delete() directive, a task can delete another task by restarting that task, and allowing that task to release resources back to RTEMS and then delete itself.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may change the priority of a task. This may cause the calling task to be preempted.
The directive may unblock a task. This may cause the calling task to be preempted.

7.4.7. rtems_task_delete()¶

Deletes the task.

CALLING SEQUENCE:

rtems_status_code rtems_task_delete( rtems_id id );

PARAMETERS:

id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.

DESCRIPTION:

This directive deletes the task, either the calling task or another task, as specified by id.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by id.
RTEMS_CALLED_FROM_ISR: The directive was called from within interrupt context.
RTEMS_INCORRECT_STATE: The task termination procedure was started, however, waiting for the terminating task would have resulted in a deadlock.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The task resided on a remote node.

NOTES:

The task deletion is done in several steps. Firstly, the task is marked as terminating. While the task life of the terminating task is protected, it executes normally until it disables the task life protection or it deletes itself. A terminating task will eventually stop its normal execution and start its termination procedure. The procedure executes in the context of the terminating task. The task termination procedure involves the destruction of POSIX key values and running the task termination user extensions. Once complete the execution of the task is stopped and task-specific resources are reclaimed by the system, such as the stack memory, any allocated delay or timeout timers, the TCB, and, if the task is RTEMS_FLOATING_POINT, its floating point context area. RTEMS explicitly does not reclaim the following resources: region segments, partition buffers, semaphores, timers, or rate monotonic periods.

A task is responsible for releasing its resources back to RTEMS before deletion. To insure proper deallocation of resources, a task should not be deleted unless it is unable to execute or does not hold any RTEMS resources. If a task holds RTEMS resources, the task should be allowed to deallocate its resources before deletion. A task can be directed to release its resources and delete itself by restarting it with a special argument or by sending it a message, an event, or a signal.

Deletion of the calling task (RTEMS_SELF) will force RTEMS to select another task to execute.

When a task deletes another task, the calling task waits until the task termination procedure of the task being deleted has completed. The terminating task inherits the eligible priorities of the calling task.

When a global task is deleted, the task identifier must be transmitted to every node in the system for deletion from the local copy of the global object table.

The task must reside on the local node, even if the task was created with the RTEMS_GLOBAL attribute.

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 directive operates on a global object, the directive sends a message to remote nodes. This may preempt the calling task.
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.

7.4.8. rtems_task_exit()¶

Deletes the calling task.

CALLING SEQUENCE:

void rtems_task_exit( void );

DESCRIPTION:

This directive deletes the calling task.

NOTES:

The directive is an optimized variant of the following code sequences, see also rtems_task_delete():

#include <pthread.h>
#include <rtems.h>

void classic_delete_self( void )
{
  (void) rtems_task_delete( RTEMS_SELF );
}

void posix_delete_self( void )
{
  (void) pthread_detach( pthread_self() );
  (void) pthread_exit( NULL);
}

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within task context.
The directive will not return to the caller.
While thread dispatching is disabled, if the directive performs a thread dispatch, then the fatal error with the fatal source INTERNAL_ERROR_CORE and the fatal code INTERNAL_ERROR_BAD_THREAD_DISPATCH_DISABLE_LEVEL will occur.

7.4.9. rtems_task_suspend()¶

Suspends the task.

CALLING SEQUENCE:

rtems_status_code rtems_task_suspend( rtems_id id );

PARAMETERS:

id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.

DESCRIPTION:

This directive suspends the task specified by id from further execution by placing it in the suspended state. This state is additive to any other blocked state that the task may already be in. The task will not execute again until another task issues the rtems_task_resume() directive for this task and any blocked state has been removed. The rtems_task_restart() directive will also remove the suspended state.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by id.
RTEMS_ALREADY_SUSPENDED: The task was already suspended.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The task resided on a remote node.

NOTES:

The requesting task can suspend itself for example by specifying RTEMS_SELF as id. In this case, the task will be suspended and a successful return code will be returned when the task is resumed.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
The directive may be called from within device driver initialization context.
The directive may be called from within task context.
When the directive operates on a remote object, the directive sends a message to the remote node and waits for a reply. This will preempt the calling task.

7.4.10. rtems_task_resume()¶

Resumes the task.

CALLING SEQUENCE:

rtems_status_code rtems_task_resume( rtems_id id );

PARAMETERS:

id: This parameter is the task identifier.

DESCRIPTION:

This directive removes the task specified by id from the suspended state. If the task is in the ready state after the suspension is removed, then it will be scheduled to run. If the task is still in a blocked state after the suspension is removed, then it will remain in that blocked state.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by id.
RTEMS_INCORRECT_STATE: The task was not suspended.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
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.
When the directive operates on a remote object, the directive sends a message to the remote node and waits for a reply. This will preempt the calling task.

7.4.11. rtems_task_is_suspended()¶

Checks if the task is suspended.

CALLING SEQUENCE:

rtems_status_code rtems_task_is_suspended( rtems_id id );

PARAMETERS:

id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.

DESCRIPTION:

This directive returns a status code indicating whether or not the task specified by id is currently suspended.

RETURN VALUES:

RTEMS_SUCCESSFUL: The task was not suspended.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by id.
RTEMS_ALREADY_SUSPENDED: The task was suspended.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The task resided on a remote node.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive will not cause the calling task to be preempted.

7.4.12. rtems_task_set_priority()¶

Sets the real priority or gets the current priority of the task.

CALLING SEQUENCE:

rtems_status_code rtems_task_set_priority(
  rtems_id             id,
  rtems_task_priority  new_priority,
  rtems_task_priority *old_priority
);

PARAMETERS:

id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.
new_priority: This parameter is the new real priority or RTEMS_CURRENT_PRIORITY to get the current priority.
old_priority: This parameter is the pointer to an rtems_task_priority object. When the directive call is successful, the current or previous priority of the task with respect to its home scheduler will be stored in this object.

DESCRIPTION:

This directive manipulates the priority of the task specified by id. When new_priority is not equal to RTEMS_CURRENT_PRIORITY, the specified task’s previous priority is returned in old_priority. When new_priority is RTEMS_CURRENT_PRIORITY, the specified task’s current priority is returned in old_priority.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The old_priority parameter was NULL.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by id.
RTEMS_INVALID_PRIORITY: The task priority specified in new_priority was invalid with respect to the home scheduler of the task.

NOTES:

Valid priorities range from one to a maximum value which depends on the configured scheduler. The lower the priority value the higher is the importance of the task.

If the task is currently holding any binary semaphores which use a locking protocol, then the task’s priority cannot be lowered immediately. If the task’s priority were lowered immediately, then this could violate properties of the locking protocol and may result in priority inversion. The requested lowering of the task’s priority will occur when the task has released all binary semaphores which make the task more important. The task’s priority can be increased regardless of the task’s use of binary semaphores with locking protocols.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may change the priority of a task. This may cause the calling task to be preempted.
When the directive operates on a remote object, the directive sends a message to the remote node and waits for a reply. This will preempt the calling task.

7.4.13. rtems_task_get_priority()¶

Gets the current priority of the task with respect to the scheduler.

CALLING SEQUENCE:

rtems_status_code rtems_task_get_priority(
  rtems_id             task_id,
  rtems_id             scheduler_id,
  rtems_task_priority *priority
);

PARAMETERS:

task_id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.
scheduler_id: This parameter is the scheduler identifier.
priority: This parameter is the pointer to an rtems_task_priority object. When the directive call is successful, the current priority of the task with respect to the specified scheduler will be stored in this object.

DESCRIPTION:

This directive returns the current priority in priority of the task specified by task_id with respect to the scheduler specified by scheduler_id.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The priority parameter was NULL.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by task_id.
RTEMS_INVALID_ID: There was no scheduler associated with the identifier specified by scheduler_id.
RTEMS_NOT_DEFINED: The task had no priority with respect to the scheduler.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The task resided on a remote node.

NOTES:

The current priority reflects temporary priority adjustments due to locking protocols, the rate-monotonic period objects on some schedulers such as EDF, and the POSIX sporadic server.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive will not cause the calling task to be preempted.

7.4.14. rtems_task_mode()¶

Gets and optionally sets the mode of the calling task.

CALLING SEQUENCE:

rtems_status_code rtems_task_mode(
  rtems_mode  mode_set,
  rtems_mode  mask,
  rtems_mode *previous_mode_set
);

PARAMETERS:

mode_set: This parameter is the mode set to apply to the calling task. When mask is set to RTEMS_CURRENT_MODE, the value of this parameter is ignored. Only modes requested by mask are applied to the calling task.
mask: This parameter is the mode mask which specifies which modes in mode_set are applied to the calling task. When the value is RTEMS_CURRENT_MODE, the mode of the calling task is not changed.
previous_mode_set: This parameter is the pointer to an rtems_mode object. When the directive call is successful, the mode of the task before any mode changes done by the directive call will be stored in this object.

DESCRIPTION:

This directive queries and optionally manipulates the execution mode of the calling task. A task’s execution mode enables and disables preemption, timeslicing, asynchronous signal processing, as well as specifying the interrupt level. To modify an execution mode, the mode class(es) to be changed must be specified in the mask parameter and the desired mode(s) must be specified in the mode_set parameter.

A task can obtain its current execution mode, without modifying it, by calling this directive with a mask value of RTEMS_CURRENT_MODE.

The mode set specified in mode_set is built through a bitwise or of the mode constants described below. Not all combinations of modes are allowed. Some modes are mutually exclusive. If mutually exclusive modes are combined, the behaviour is undefined. Default task modes can be selected by using the RTEMS_DEFAULT_MODES constant. The task mode set defines

the preemption mode of the task: RTEMS_PREEMPT (default) or RTEMS_NO_PREEMPT,
the timeslicing mode of the task: RTEMS_TIMESLICE or RTEMS_NO_TIMESLICE (default),
the ASR processing mode of the task: RTEMS_ASR (default) or RTEMS_NO_ASR,
the interrupt level of the task: RTEMS_INTERRUPT_LEVEL() with a default of RTEMS_INTERRUPT_LEVEL( 0 ) which is associated with enabled interrupts.

The mode mask specified in mask is built through a bitwise or of the mode mask constants described below.

When the RTEMS_PREEMPT_MASK is set in mask, the preemption mode of the calling task is

enabled by using the RTEMS_PREEMPT mode constant in mode_set and
disabled by using the RTEMS_NO_PREEMPT mode constant in mode_set.

When the RTEMS_TIMESLICE_MASK is set in mask, the timeslicing mode of the calling task is

enabled by using the RTEMS_TIMESLICE mode constant in mode_set and
disabled by using the RTEMS_NO_TIMESLICE mode constant in mode_set.

Enabling timeslicing has no effect if preemption is disabled. For a task to be timesliced, that task must have both preemption and timeslicing enabled.

When the RTEMS_ASR_MASK is set in mask, the ASR processing mode of the calling task is

enabled by using the RTEMS_ASR mode constant in mode_set and
disabled by using the RTEMS_NO_ASR mode constant in mode_set.

When the RTEMS_INTERRUPT_MASK is set in mask, interrupts of the calling task are

enabled by using the RTEMS_INTERRUPT_LEVEL() mode macro with a value of zero (0) in mode_set and
disabled up to the specified level by using the RTEMS_INTERRUPT_LEVEL() mode macro with a positive value in mode_set.

An interrupt level of zero is associated with enabled interrupts on all target processors. The interrupt level portion of the task mode supports a maximum of 256 interrupt levels. These levels are mapped onto the interrupt levels actually supported by the target processor in a processor dependent fashion.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_NOT_IMPLEMENTED: The RTEMS_NO_PREEMPT was set in mode_set and setting the preemption mode was requested by RTEMS_PREEMPT_MASK in mask and the system configuration had no implementation for this mode.
RTEMS_NOT_IMPLEMENTED: The RTEMS_INTERRUPT_LEVEL() was set to a positive level in mode_set and setting the interrupt level was requested by RTEMS_INTERRUPT_MASK in mask and the system configuration had no implementation for this mode.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within task context.
When the directive enables preemption for the calling task, another task may preempt the calling task.
While thread dispatching is disabled, if the directive performs a thread dispatch, then the fatal error with the fatal source INTERNAL_ERROR_CORE and the fatal code INTERNAL_ERROR_BAD_THREAD_DISPATCH_DISABLE_LEVEL will occur.

7.4.15. rtems_task_wake_after()¶

Wakes up after a count of clock ticks have occurred or yields the processor.

CALLING SEQUENCE:

rtems_status_code rtems_task_wake_after( rtems_interval ticks );

PARAMETERS:

ticks: This parameter is the count of clock ticks to delay the task or RTEMS_YIELD_PROCESSOR to yield the processor.

DESCRIPTION:

This directive blocks the calling task for the specified ticks count of clock ticks if the value is not equal to RTEMS_YIELD_PROCESSOR. When the requested count of ticks have occurred, the task is made ready. The clock tick directives automatically update the delay period. The calling task may give up the processor and remain in the ready state by specifying a value of RTEMS_YIELD_PROCESSOR in ticks.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.

NOTES:

Setting the system date and time with the rtems_clock_set() directive and similar directives which set CLOCK_REALTIME have no effect on a rtems_task_wake_after() blocked task. The delay until first clock tick will never be a whole clock tick interval since this directive will never execute exactly on a clock tick. Applications requiring use of a clock (CLOCK_REALTIME or CLOCK_MONOTONIC) instead of clock ticks should make use of clock_nanosleep().

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within task context.
The directive requires a Clock Driver.
While thread dispatching is disabled, if the directive performs a thread dispatch, then the fatal error with the fatal source INTERNAL_ERROR_CORE and the fatal code INTERNAL_ERROR_BAD_THREAD_DISPATCH_DISABLE_LEVEL will occur.

7.4.16. rtems_task_wake_when()¶

Wakes up when specified.

CALLING SEQUENCE:

rtems_status_code rtems_task_wake_when( const rtems_time_of_day *time_buffer );

PARAMETERS:

time_buffer: This parameter is the date and time to wake up.

DESCRIPTION:

This directive blocks a task until the date and time specified in time_buffer. At the requested date and time, the calling task will be unblocked and made ready to execute.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_NOT_DEFINED: The system date and time was not set.
RTEMS_INVALID_ADDRESS: The time_buffer parameter was NULL.
RTEMS_INVALID_CLOCK: The time of day was invalid.

NOTES:

The ticks portion of time_buffer structure is ignored. The timing granularity of this directive is a second.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within task context.
The directive requires a Clock Driver.
While thread dispatching is disabled, if the directive performs a thread dispatch, then the fatal error with the fatal source INTERNAL_ERROR_CORE and the fatal code INTERNAL_ERROR_BAD_THREAD_DISPATCH_DISABLE_LEVEL will occur.

7.4.17. rtems_task_get_scheduler()¶

Gets the home scheduler of the task.

CALLING SEQUENCE:

rtems_status_code rtems_task_get_scheduler(
  rtems_id  task_id,
  rtems_id *scheduler_id
);

PARAMETERS:

task_id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.
scheduler_id: This parameter is the pointer to an rtems_id object. When the directive call is successful, the identifier of the home scheduler of the task will be stored in this object.

DESCRIPTION:

This directive returns the identifier of the home scheduler of the task specified by task_id in scheduler_id.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The scheduler_id parameter was NULL.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by task_id.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The task resided on a remote node.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive will not cause the calling task to be preempted.

7.4.18. rtems_task_set_scheduler()¶

Sets the home scheduler for the task.

CALLING SEQUENCE:

rtems_status_code rtems_task_set_scheduler(
  rtems_id            task_id,
  rtems_id            scheduler_id,
  rtems_task_priority priority
);

PARAMETERS:

task_id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.
scheduler_id: This parameter is the scheduler identifier of the new home scheduler for the task specified by task_id.
priority: This parameter is the new real priority for the task with respect to the scheduler specified by scheduler_id.

DESCRIPTION:

This directive sets the home scheduler to the scheduler specified by scheduler_id for the task specified by task_id.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ID: There was no scheduler associated with the identifier specified by scheduler_id.
RTEMS_INVALID_PRIORITY: The task priority specified by priority was invalid with respect to the scheduler specified by scheduler_id.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by task_id.
RTEMS_RESOURCE_IN_USE: The task specified by task_id was enqueued on a wait queue.
RTEMS_RESOURCE_IN_USE: The task specified by task_id had a current priority which consisted of more than the real priority.
RTEMS_RESOURCE_IN_USE: The task specified by task_id had a helping scheduler.
RTEMS_RESOURCE_IN_USE: The task specified by task_id was pinned.
RTEMS_UNSATISFIED: The scheduler specified by scheduler_id owned no processor.
RTEMS_UNSATISFIED: The scheduler specified by scheduler_id did not support the affinity set of the task specified by task_id.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The task resided on a remote node.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may change the priority of a task. This may cause the calling task to be preempted.

7.4.19. rtems_task_get_affinity()¶

Gets the processor affinity of the task.

CALLING SEQUENCE:

rtems_status_code rtems_task_get_affinity(
  rtems_id   id,
  size_t     cpusetsize,
  cpu_set_t *cpuset
);

PARAMETERS:

id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.
cpusetsize: This parameter is the size of the processor set referenced by cpuset in bytes.
cpuset: This parameter is the pointer to a cpu_set_t object. When the directive call is successful, the processor affinity set of the task will be stored in this object. A set bit in the processor set means that the corresponding processor is in the processor affinity set of the task, otherwise the bit is cleared.

DESCRIPTION:

This directive returns the processor affinity of the task in cpuset of the task specified by id.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The cpuset parameter was NULL.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by id.
RTEMS_INVALID_SIZE: The size specified by cpusetsize of the processor set was too small for the processor affinity set of the task.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The task resided on a remote node.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive will not cause the calling task to be preempted.

7.4.20. rtems_task_set_affinity()¶

Sets the processor affinity of the task.

CALLING SEQUENCE:

rtems_status_code rtems_task_set_affinity(
  rtems_id         id,
  size_t           cpusetsize,
  const cpu_set_t *cpuset
);

PARAMETERS:

id: This parameter is the task identifier. The constant RTEMS_SELF may be used to specify the calling task.
cpusetsize: This parameter is the size of the processor set referenced by cpuset in bytes.
cpuset: This parameter is the pointer to a cpu_set_t object. The processor set defines the new processor affinity set of the task. A set bit in the processor set means that the corresponding processor shall be in the processor affinity set of the task, otherwise the bit shall be cleared.

DESCRIPTION:

This directive sets the processor affinity of the task specified by id.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The cpuset parameter was NULL.
RTEMS_INVALID_ID: There was no task associated with the identifier specified by id.
RTEMS_INVALID_NUMBER: The referenced processor set was not a valid new processor affinity set for the task.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The task resided on a remote node.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within interrupt context.
The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may change the processor affinity of a task. This may cause the calling task to be preempted.

7.4.21. rtems_task_iterate()¶

Iterates over all tasks and invokes the visitor routine for each task.

CALLING SEQUENCE:

void rtems_task_iterate( rtems_task_visitor visitor, void *arg );

PARAMETERS:

visitor: This parameter is the visitor routine invoked for each task.
arg: This parameter is the argument passed to each visitor routine invocation during the iteration.

DESCRIPTION:

This directive iterates over all tasks in the system. This operation covers all tasks of all APIs. The user should be careful in accessing the contents of the TCB. The visitor argument arg is passed to all invocations of visitor in addition to the TCB. The iteration stops immediately in case the visitor routine returns true.

NOTES:

The visitor routine is invoked while owning the objects allocator lock. It is allowed to perform blocking operations in the visitor routine, however, care must be taken so that no deadlocks via the object allocator lock can occur.

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.

7.4.22. RTEMS_TASK_STORAGE_SIZE()¶

Gets the recommended task storage area size for the size and task attributes.

CALLING SEQUENCE:

size_t RTEMS_TASK_STORAGE_SIZE( size_t size, rtems_attribute attributes );

PARAMETERS:

size: This parameter is the size dedicated to the task stack and thread-local storage in bytes.
attributes: This parameter is the attribute set of the task using the storage area.

RETURN VALUES:

Returns the recommended task storage area size calculated from the input parameters.