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diff --git a/c-user/event/operations.rst b/c-user/event/operations.rst new file mode 100644 index 0000000..e01b6dc --- /dev/null +++ b/c-user/event/operations.rst @@ -0,0 +1,63 @@ +.. SPDX-License-Identifier: CC-BY-SA-4.0 + +.. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR) + +Operations +========== + +Sending an Event Set +-------------------- + +The ``rtems_event_send`` directive allows a task (or an ISR) to direct an event +set to a target task. Based upon the state of the target task, one of the +following situations applies: + +- Target Task is Blocked Waiting for Events + + - If the waiting task's input event condition is satisfied, then the task is + made ready for execution. + + - If the waiting task's input event condition is not satisfied, then the + event set is posted but left pending and the task remains blocked. + +- Target Task is Not Waiting for Events + + - The event set is posted and left pending. + +Receiving an Event Set +---------------------- + +The ``rtems_event_receive`` directive is used by tasks to accept a specific +input event condition. The task also specifies whether the request is +satisfied when all requested events are available or any single requested event +is available. If the requested event condition is satisfied by pending events, +then a successful return code and the satisfying event set are returned +immediately. If the condition is not satisfied, then one of the following +situations applies: + +- By default, the calling task will wait forever for the event condition to be + satisfied. + +- Specifying the ``RTEMS_NO_WAIT`` option forces an immediate return with an + error status code. + +- Specifying a timeout limits the period the task will wait before returning + with an error status code. + +Determining the Pending Event Set +--------------------------------- + +A task can determine the pending event set by calling the +``rtems_event_receive`` directive with a value of ``RTEMS_PENDING_EVENTS`` for +the input event condition. The pending events are returned to the calling task +but the event set is left unaltered. + +Receiving all Pending Events +---------------------------- + +A task can receive all of the currently pending events by calling the +``rtems_event_receive`` directive with a value of ``RTEMS_ALL_EVENTS`` for the +input event condition and ``RTEMS_NO_WAIT | RTEMS_EVENT_ANY`` for the option +set. The pending events are returned to the calling task and the event set is +cleared. If no events are pending then the ``RTEMS_UNSATISFIED`` status code +will be returned. |