diff options
Diffstat (limited to 'c-user/timer_manager.rst')
| -rw-r--r-- | c-user/timer_manager.rst | 634 |
1 files changed, 634 insertions, 0 deletions
diff --git a/c-user/timer_manager.rst b/c-user/timer_manager.rst new file mode 100644 index 0000000..2b1f2f5 --- /dev/null +++ b/c-user/timer_manager.rst @@ -0,0 +1,634 @@ +.. comment SPDX-License-Identifier: CC-BY-SA-4.0 + +.. COMMENT: COPYRIGHT (c) 1988-2008. +.. COMMENT: On-Line Applications Research Corporation (OAR). +.. COMMENT: All rights reserved. + +Timer Manager +############# + +.. index:: timers + +Introduction +============ + +The timer manager provides support for timer +facilities. The directives provided by the timer manager are: + +- rtems_timer_create_ - Create a timer + +- rtems_timer_ident_ - Get ID of a timer + +- rtems_timer_cancel_ - Cancel a timer + +- rtems_timer_delete_ - Delete a timer + +- rtems_timer_fire_after_ - Fire timer after interval + +- rtems_timer_fire_when_ - Fire timer when specified + +- rtems_timer_initiate_server_ - Initiate server for task-based timers + +- rtems_timer_server_fire_after_ - Fire task-based timer after interval + +- rtems_timer_server_fire_when_ - Fire task-based timer when specified + +- rtems_timer_reset_ - Reset an interval timer + +Background +========== + +Required Support +---------------- + +A clock tick is required to support the functionality provided by this manager. + +Timers +------ + +A timer is an RTEMS object which allows the application to schedule operations +to occur at specific times in the future. User supplied timer service routines +are invoked by either the ``rtems_clock_tick`` directive or a special Timer +Server task when the timer fires. Timer service routines may perform any +operations or directives which normally would be performed by the application +code which invoked the ``rtems_clock_tick`` directive. + +The timer can be used to implement watchdog routines which only fire to denote +that an application error has occurred. The timer is reset at specific points +in the application to ensure that the watchdog does not fire. Thus, if the +application does not reset the watchdog timer, then the timer service routine +will fire to indicate that the application has failed to reach a reset point. +This use of a timer is sometimes referred to as a "keep alive" or a "deadman" +timer. + +Timer Server +------------ + +The Timer Server task is responsible for executing the timer service routines +associated with all task-based timers. This task executes at a priority higher +than any RTEMS application task, and is created non-preemptible, and thus can +be viewed logically as the lowest priority interrupt. + +By providing a mechanism where timer service routines execute in task rather +than interrupt space, the application is allowed a bit more flexibility in what +operations a timer service routine can perform. For example, the Timer Server +can be configured to have a floating point context in which case it would be +safe to perform floating point operations from a task-based timer. Most of the +time, executing floating point instructions from an interrupt service routine +is not considered safe. However, since the Timer Server task is +non-preemptible, only directives allowed from an ISR can be called in the timer +service routine. + +The Timer Server is designed to remain blocked until a task-based timer fires. +This reduces the execution overhead of the Timer Server. + +Timer Service Routines +---------------------- + +The timer service routine should adhere to C calling conventions and have a +prototype similar to the following: + +.. index:: rtems_timer_service_routine + +.. code-block:: c + + rtems_timer_service_routine user_routine( + rtems_id timer_id, + void *user_data + ); + +Where the timer_id parameter is the RTEMS object ID of the timer which is being +fired and user_data is a pointer to user-defined information which may be +utilized by the timer service routine. The argument user_data may be NULL. + +Operations +========== + +Creating a Timer +---------------- + +The ``rtems_timer_create`` directive creates a timer by allocating a Timer +Control Block (TMCB), assigning the timer a user-specified name, and assigning +it a timer ID. Newly created timers do not have a timer service routine +associated with them and are not active. + +Obtaining Timer IDs +------------------- + +When a timer is created, RTEMS generates a unique timer ID and assigns it to +the created timer until it is deleted. The timer ID may be obtained by either +of two methods. First, as the result of an invocation of the +``rtems_timer_create`` directive, the timer ID is stored in a user provided +location. Second, the timer ID may be obtained later using the +``rtems_timer_ident`` directive. The timer ID is used by other directives to +manipulate this timer. + +Initiating an Interval Timer +---------------------------- + +The ``rtems_timer_fire_after`` and ``rtems_timer_server_fire_after`` directives +initiate a timer to fire a user provided timer service routine after the +specified number of clock ticks have elapsed. When the interval has elapsed, +the timer service routine will be invoked from the ``rtems_clock_tick`` +directive if it was initiated by the ``rtems_timer_fire_after`` directive and +from the Timer Server task if initiated by the +``rtems_timer_server_fire_after`` directive. + +Initiating a Time of Day Timer +------------------------------ + +The ``rtems_timer_fire_when`` and ``rtems_timer_server_fire_when`` directive +initiate a timer to fire a user provided timer service routine when the +specified time of day has been reached. When the interval has elapsed, the +timer service routine will be invoked from the ``rtems_clock_tick`` directive +by the ``rtems_timer_fire_when`` directive and from the Timer Server task if +initiated by the ``rtems_timer_server_fire_when`` directive. + +Canceling a Timer +----------------- + +The ``rtems_timer_cancel`` directive is used to halt the specified timer. Once +canceled, the timer service routine will not fire unless the timer is +reinitiated. The timer can be reinitiated using the ``rtems_timer_reset``, +``rtems_timer_fire_after``, and ``rtems_timer_fire_when`` directives. + +Resetting a Timer +----------------- + +The ``rtems_timer_reset`` directive is used to restore an interval timer +initiated by a previous invocation of ``rtems_timer_fire_after`` or +``rtems_timer_server_fire_after`` to its original interval length. If the +timer has not been used or the last usage of this timer was by the +``rtems_timer_fire_when`` or ``rtems_timer_server_fire_when`` directive, then +an error is returned. The timer service routine is not changed or fired by +this directive. + +Initiating the Timer Server +--------------------------- + +The ``rtems_timer_initiate_server`` directive is used to allocate and start the +execution of the Timer Server task. The application can specify both the stack +size and attributes of the Timer Server. The Timer Server executes at a +priority higher than any application task and thus the user can expect to be +preempted as the result of executing the ``rtems_timer_initiate_server`` +directive. + +Deleting a Timer +---------------- + +The ``rtems_timer_delete`` directive is used to delete a timer. If the timer +is running and has not expired, the timer is automatically canceled. The +timer's control block is returned to the TMCB free list when it is deleted. A +timer can be deleted by a task other than the task which created the timer. +Any subsequent references to the timer's name and ID are invalid. + +Directives +========== + +This section details the timer manager's directives. A subsection is dedicated +to each of this manager's directives and describes the calling sequence, +related constants, usage, and status codes. + +.. _rtems_timer_create: + +TIMER_CREATE - Create a timer +----------------------------- +.. index:: create a timer + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_create + +.. code-block:: c + + rtems_status_code rtems_timer_create( + rtems_name name, + rtems_id *id + ); + +**DIRECTIVE STATUS CODES:** + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_SUCCESSFUL`` + - timer created successfully + * - ``RTEMS_INVALID_ADDRESS`` + - ``id`` is NULL + * - ``RTEMS_INVALID_NAME`` + - invalid timer name + * - ``RTEMS_TOO_MANY`` + - too many timers created + +**DESCRIPTION:** + +This directive creates a timer. The assigned timer id is returned in id. This +id is used to access the timer with other timer manager directives. For +control and maintenance of the timer, RTEMS allocates a TMCB from the local +TMCB free pool and initializes it. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +.. _rtems_timer_ident: + +TIMER_IDENT - Get ID of a timer +------------------------------- +.. index:: obtain the ID of a timer + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_ident + +.. code-block:: c + + rtems_status_code rtems_timer_ident( + rtems_name name, + rtems_id *id + ); + +**DIRECTIVE STATUS CODES:** + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_SUCCESSFUL`` + - timer identified successfully + * - ``RTEMS_INVALID_ADDRESS`` + - ``id`` is NULL + * - ``RTEMS_INVALID_NAME`` + - timer name not found + +**DESCRIPTION:** + +This directive obtains the timer id associated with the timer name to be +acquired. If the timer name is not unique, then the timer id will match one of +the timers with that name. However, this timer id is not guaranteed to +correspond to the desired timer. The timer id is used to access this timer in +other timer related directives. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +.. _rtems_timer_cancel: + +TIMER_CANCEL - Cancel a timer +----------------------------- +.. index:: cancel a timer + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_cancel + +.. code-block:: c + + rtems_status_code rtems_timer_cancel( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_SUCCESSFUL`` + - timer canceled successfully + * - ``RTEMS_INVALID_ID`` + - invalid timer id + +**DESCRIPTION:** + +This directive cancels the timer id. This timer will be reinitiated by the +next invocation of ``rtems_timer_reset``, ``rtems_timer_fire_after``, or +``rtems_timer_fire_when`` with this id. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +.. _rtems_timer_delete: + +TIMER_DELETE - Delete a timer +----------------------------- +.. index:: delete a timer + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_delete + +.. code-block:: c + + rtems_status_code rtems_timer_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_SUCCESSFUL`` + - timer deleted successfully + * - ``RTEMS_INVALID_ID`` + - invalid timer id + +**DESCRIPTION:** + +This directive deletes the timer specified by id. If the timer is running, it +is automatically canceled. The TMCB for the deleted timer is reclaimed by +RTEMS. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +A timer can be deleted by a task other than the task which created the timer. + +.. _rtems_timer_fire_after: + +TIMER_FIRE_AFTER - Fire timer after interval +-------------------------------------------- +.. index:: fire a timer after an interval + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_fire_after + +.. code-block:: c + + rtems_status_code rtems_timer_fire_after( + rtems_id id, + rtems_interval ticks, + rtems_timer_service_routine_entry routine, + void *user_data + ); + +**DIRECTIVE STATUS CODES:** + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_SUCCESSFUL`` + - timer initiated successfully + * - ``RTEMS_INVALID_ADDRESS`` + - ``routine`` is NULL + * - ``RTEMS_INVALID_ID`` + - invalid timer id + * - ``RTEMS_INVALID_NUMBER`` + - invalid interval + +**DESCRIPTION:** + +This directive initiates the timer specified by id. If the timer is running, +it is automatically canceled before being initiated. The timer is scheduled to +fire after an interval ticks clock ticks has passed. When the timer fires, the +timer service routine routine will be invoked with the argument user_data. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +.. _rtems_timer_fire_when: + +TIMER_FIRE_WHEN - Fire timer when specified +------------------------------------------- +.. index:: fire a timer at wall time + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_fire_when + +.. code-block:: c + + rtems_status_code rtems_timer_fire_when( + rtems_id id, + rtems_time_of_day *wall_time, + rtems_timer_service_routine_entry routine, + void *user_data + ); + +**DIRECTIVE STATUS CODES:** + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_SUCCESSFUL`` + - timer initiated successfully + * - ``RTEMS_INVALID_ADDRESS`` + - ``routine`` is NULL + * - ``RTEMS_INVALID_ADDRESS`` + - ``wall_time`` is NULL + * - ``RTEMS_INVALID_ID`` + - invalid timer id + * - ``RTEMS_NOT_DEFINED`` + - system date and time is not set + * - ``RTEMS_INVALID_CLOCK`` + - invalid time of day + +**DESCRIPTION:** + +This directive initiates the timer specified by id. If the timer is running, +it is automatically canceled before being initiated. The timer is scheduled to +fire at the time of day specified by wall_time. When the timer fires, the +timer service routine routine will be invoked with the argument user_data. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +.. _rtems_timer_initiate_server: + +TIMER_INITIATE_SERVER - Initiate server for task-based timers +------------------------------------------------------------- +.. index:: initiate the Timer Server + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_initiate_server + +.. code-block:: c + + rtems_status_code rtems_timer_initiate_server( + uint32_t priority, + uint32_t stack_size, + rtems_attribute attribute_set + ); + +**DIRECTIVE STATUS CODES:** + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_SUCCESSFUL`` + - Timer Server initiated successfully + * - ``RTEMS_TOO_MANY`` + - too many tasks created + +**DESCRIPTION:** + +This directive initiates the Timer Server task. This task is responsible for +executing all timers initiated via the ``rtems_timer_server_fire_after`` or +``rtems_timer_server_fire_when`` directives. + +**NOTES:** + +This directive could cause the calling task to be preempted. + +The Timer Server task is created using the ``rtems_task_create`` service and +must be accounted for when configuring the system. + +Even through this directive invokes the ``rtems_task_create`` and +``rtems_task_start`` directives, it should only fail due to resource allocation +problems. + +.. _rtems_timer_server_fire_after: + +TIMER_SERVER_FIRE_AFTER - Fire task-based timer after interval +-------------------------------------------------------------- +.. index:: fire task-based a timer after an interval + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_server_fire_after + +.. code-block:: c + + rtems_status_code rtems_timer_server_fire_after( + rtems_id id, + rtems_interval ticks, + rtems_timer_service_routine_entry routine, + void *user_data + ); + +**DIRECTIVE STATUS CODES:** + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_SUCCESSFUL`` + - timer initiated successfully + * - ``RTEMS_INVALID_ADDRESS`` + - ``routine`` is NULL + * - ``RTEMS_INVALID_ID`` + - invalid timer id + * - ``RTEMS_INVALID_NUMBER`` + - invalid interval + * - ``RTEMS_INCORRECT_STATE`` + - Timer Server not initiated + +**DESCRIPTION:** + +This directive initiates the timer specified by id and specifies that when it +fires it will be executed by the Timer Server. + +If the timer is running, it is automatically canceled before being initiated. +The timer is scheduled to fire after an interval ticks clock ticks has passed. +When the timer fires, the timer service routine routine will be invoked with +the argument user_data. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +.. _rtems_timer_server_fire_when: + +TIMER_SERVER_FIRE_WHEN - Fire task-based timer when specified +------------------------------------------------------------- +.. index:: fire a task-based timer at wall time + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_server_fire_when + +.. code-block:: c + + rtems_status_code rtems_timer_server_fire_when( + rtems_id id, + rtems_time_of_day *wall_time, + rtems_timer_service_routine_entry routine, + void *user_data + ); + +**DIRECTIVE STATUS CODES:** + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_SUCCESSFUL`` + - timer initiated successfully + * - ``RTEMS_INVALID_ADDRESS`` + - ``routine`` is NULL + * - ``RTEMS_INVALID_ADDRESS`` + - ``wall_time`` is NULL + * - ``RTEMS_INVALID_ID`` + - invalid timer id + * - ``RTEMS_NOT_DEFINED`` + - system date and time is not set + * - ``RTEMS_INVALID_CLOCK`` + - invalid time of day + * - ``RTEMS_INCORRECT_STATE`` + - Timer Server not initiated + +**DESCRIPTION:** + +This directive initiates the timer specified by id and specifies that when it +fires it will be executed by the Timer Server. + +If the timer is running, it is automatically canceled before being initiated. +The timer is scheduled to fire at the time of day specified by wall_time. When +the timer fires, the timer service routine routine will be invoked with the +argument user_data. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +.. _rtems_timer_reset: + +TIMER_RESET - Reset an interval timer +------------------------------------- +.. index:: reset a timer + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_reset + +.. code-block:: c + + rtems_status_code rtems_timer_reset( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_SUCCESSFUL`` + - timer reset successfully + * - ``RTEMS_INVALID_ID`` + - invalid timer id + * - ``RTEMS_NOT_DEFINED`` + - attempted to reset a when or newly created timer + +**DESCRIPTION:** + +This directive resets the timer associated with id. This timer must have been +previously initiated with either the ``rtems_timer_fire_after`` or +``rtems_timer_server_fire_after`` directive. If active the timer is canceled, +after which the timer is reinitiated using the same interval and timer service +routine which the original ``rtems_timer_fire_after`` or +``rtems_timer_server_fire_after`` directive used. + +**NOTES:** + +If the timer has not been used or the last usage of this timer was by a +``rtems_timer_fire_when`` or ``rtems_timer_server_fire_when`` directive, then +the ``RTEMS_NOT_DEFINED`` error is returned. + +Restarting a cancelled after timer results in the timer being reinitiated with +its previous timer service routine and interval. + +This directive will not cause the running task to be preempted. |