15.3. Operations

15.3.1. 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.

15.3.2. 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.

15.3.3. 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.

15.3.4. 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.