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<div class="title">xSemaphoreGiveFromISR</div> </div>
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<p>semphr. h </p><pre>
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xSemaphoreGiveFromISR(
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SemaphoreHandle_t xSemaphore,
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BaseType_t *pxHigherPriorityTaskWoken
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)</pre><p><em>Macro</em> to release a semaphore. The semaphore must have previously been created with a call to xSemaphoreCreateBinary() or xSemaphoreCreateCounting().</p>
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<p>Mutex type semaphores (those created using a call to xSemaphoreCreateMutex()) must not be used with this macro.</p>
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<p>This macro can be used from an ISR.</p>
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<dl class="params"><dt>Parameters</dt><dd>
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<table class="params">
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<tr><td class="paramname">xSemaphore</td><td>A handle to the semaphore being released. This is the handle returned when the semaphore was created.</td></tr>
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<tr><td class="paramname">pxHigherPriorityTaskWoken</td><td><a class="el" href="semphr_8h.html#a68aa43df8b2a0dbe17d05fad74670ef0">xSemaphoreGiveFromISR()</a> will set *pxHigherPriorityTaskWoken to pdTRUE if giving the semaphore caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If <a class="el" href="semphr_8h.html#a68aa43df8b2a0dbe17d05fad74670ef0">xSemaphoreGiveFromISR()</a> sets this value to pdTRUE then a context switch should be requested before the interrupt is exited.</td></tr>
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</table>
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</dd>
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</dl>
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<dl class="section return"><dt>Returns</dt><dd>pdTRUE if the semaphore was successfully given, otherwise errQUEUE_FULL.</dd></dl>
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<p>Example usage: </p><pre>
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#define LONG_TIME 0xffff
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#define TICKS_TO_WAIT 10
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SemaphoreHandle_t xSemaphore = NULL;</pre><pre>// Repetitive task.
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void vATask( void * pvParameters )
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{
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for( ;; )
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{
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// We want this task to run every 10 ticks of a timer. The semaphore
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// was created before this task was started.</pre><pre> // Block waiting for the semaphore to become available.
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if( <a class="el" href="semphr_8h.html#af116e436d2a5ae5bd72dbade2b5ea930">xSemaphoreTake( xSemaphore, LONG_TIME )</a> == pdTRUE )
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{
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// It is time to execute.</pre><pre> // ...</pre><pre> // We have finished our task. Return to the top of the loop where
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// we will block on the semaphore until it is time to execute
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// again. Note when using the semaphore for synchronisation with an
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// ISR in this manner there is no need to 'give' the semaphore back.
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}
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}
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}</pre><pre>// Timer ISR
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void vTimerISR( void * pvParameters )
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{
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static uint8_t ucLocalTickCount = 0;
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static BaseType_t xHigherPriorityTaskWoken;</pre><pre> // A timer tick has occurred.</pre><pre> // ... Do other time functions.</pre><pre> // Is it time for vATask () to run?
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xHigherPriorityTaskWoken = pdFALSE;
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ucLocalTickCount++;
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if( ucLocalTickCount >= TICKS_TO_WAIT )
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{
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// Unblock the task by releasing the semaphore.
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<a class="el" href="semphr_8h.html#a68aa43df8b2a0dbe17d05fad74670ef0">xSemaphoreGiveFromISR( xSemaphore, &xHigherPriorityTaskWoken )</a>;</pre><pre> // Reset the count so we release the semaphore again in 10 ticks time.
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ucLocalTickCount = 0;
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}</pre><pre> if( xHigherPriorityTaskWoken != pdFALSE )
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{
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// We can force a context switch here. Context switching from an
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// ISR uses port specific syntax. Check the demo task for your port
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// to find the syntax required.
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}
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}
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