Chapter 2. API Reference
the Blocked state, waiting for messages to arrive on the timer command queue. Calling xTimer-
StartFromISR() writes a message to the timer command queue, so has the potential to transition
the timer service/daemon task out of the Blocked state. If calling xTimerStartFromISR() causes
the timer service/daemon task to leave the Blocked state, and the timer service/ daemon task has
a priority equal to or greater than the currently executing task (the task that was interrupted), then
*pxHigherPriorityTaskWoken will get set to pdTRUE internally within the xTimerStartFromISR()
function. If xTimerStartFromISR() sets this value to pdTRUE then a context switch should be per-
formed before the interrupt exits.
xTimerStopFromISR(xTimer, pxHigherPriorityTaskWoken)
BaseType_t xTimerStopFromISR( TimerHandle_t xTimer, BaseType_t *pxHigherPriorityTaskWoken );
A version of xTimerStop() that can be called from an interrupt service routine.
Example usage:
* // This scenario assumes xTimer has already been created and started. When
* // an interrupt occurs, the timer should be simply stopped.
*
* // The interrupt service routine that stops the timer.
* void vAnExampleInterruptServiceRoutine( void )
* {
* BaseType_t xHigherPriorityTaskWoken = pdFALSE;
*
* // The interrupt has occurred - simply stop the timer.
* // xHigherPriorityTaskWoken was set to pdFALSE where it was defined
* // (within this function). As this is an interrupt service routine, only
* // FreeRTOS API functions that end in "FromISR" can be used.
* if( xTimerStopFromISR( xTimer, &xHigherPriorityTaskWoken ) != pdPASS )
* {
* // The stop command was not executed successfully. Take appropriate
* // action here.
* }
*
* // If xHigherPriorityTaskWoken equals pdTRUE, then a context switch
* // should be performed. The syntax required to perform a context switch
* // from inside an ISR varies from port to port, and from compiler to
* // compiler. Inspect the demos for the port you are using to find the
* // actual syntax required.
* if( xHigherPriorityTaskWoken != pdFALSE )
* {
* // Call the interrupt safe yield function here (actual function
* // depends on the FreeRTOS port being used).
* }
* }
*
Return pdFAIL will be returned if the stop command could not be sent to the timer command queue. pdPASS
will be returned if the command was successfully sent to the timer command queue. When the command
is actually processed will depend on the priority of the timer service/daemon task relative to other tasks
in the system. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY
configuration constant.
Parameters
• xTimer: The handle of the timer being stopped.
• pxHigherPriorityTaskWoken: The timer service/daemon task spends most of its time in
the Blocked state, waiting for messages to arrive on the timer command queue. Calling xTimer-
StopFromISR() writes a message to the timer command queue, so has the potential to transition
the timer service/daemon task out of the Blocked state. If calling xTimerStopFromISR() causes
the timer service/daemon task to leave the Blocked state, and the timer service/ daemon task has
a priority equal to or greater than the currently executing task (the task that was interrupted), then
*pxHigherPriorityTaskWoken will get set to pdTRUE internally within the xTimerStopFromISR()
function. If xTimerStopFromISR() sets this value to pdTRUE then a context switch should be per-
Espressif Systems 928
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