xSemaphoreGiveFromISR macro

semphr. h @code{c} xSemaphoreGiveFromISR( SemaphoreHandle_t xSemaphore, BaseType_t *pxHigherPriorityTaskWoken ); @endcode Macro to release a semaphore. The semaphore must have previously been created with a call to xSemaphoreCreateBinary() or xSemaphoreCreateCounting(). Mutex type semaphores (those created using a call to xSemaphoreCreateMutex()) must not be used with this macro. This macro can be used from an ISR. Example usage: @code{c} \#define LONG_TIME 0xffff \#define TICKS_TO_WAIT 10 SemaphoreHandle_t xSemaphore = NULL; // Repetitive task. void vATask( void * pvParameters ) { for( ;; ) { // We want this task to run every 10 ticks of a timer. The semaphore // was created before this task was started. // Block waiting for the semaphore to become available. if( xSemaphoreTake( xSemaphore, LONG_TIME ) == pdTRUE ) { // It is time to execute. // ... // We have finished our task. Return to the top of the loop where // we will block on the semaphore until it is time to execute // again. Note when using the semaphore for synchronisation with an // ISR in this manner there is no need to 'give' the semaphore back. } } } // Timer ISR void vTimerISR( void * pvParameters ) { static uint8_t ucLocalTickCount = 0; static BaseType_t xHigherPriorityTaskWoken; // A timer tick has occurred. // ... Do other time functions. // Is it time for vATask () to run? xHigherPriorityTaskWoken = pdFALSE; ucLocalTickCount++; if( ucLocalTickCount >= TICKS_TO_WAIT ) { // Unblock the task by releasing the semaphore. xSemaphoreGiveFromISR( xSemaphore, &xHigherPriorityTaskWoken ); // Reset the count so we release the semaphore again in 10 ticks time. ucLocalTickCount = 0; } if( xHigherPriorityTaskWoken != pdFALSE ) { // We can force a context switch here. Context switching from an // ISR uses port specific syntax. Check the demo task for your port // to find the syntax required. } } @endcode