xQueueOverwriteFromISR
[Queue Management]

 BaseType_t xQueueOverwrite
                   (
                      QueueHandle_t xQueue,
                      const void * pvItemToQueue
                      BaseType_t *pxHigherPriorityTaskWoken
                    );
 

This is a macro that calls the xQueueGenericSendFromISR() function.

A version of xQueueOverwrite() that can be used in an ISR. xQueueOverwriteFromISR() is similar to xQueueSendToBackFromISR(), but will write to the queue even if the queue is full, overwriting data that is already held in the queue.

xQueueOverwriteFromISR() is intended for use with queues that have a length of one, meaning the queue is either empty or full.

Parameters:

xQueue	The handle of the queue to which the data is to be sent.
pvItemToQueue	A pointer to the item that is to be placed in the queue. The size of the items the queue will hold was defined when the queue was created, and that many bytes will be copied from pvItemToQueue into the queue storage area.
pxHigherPriorityTaskWoken	xQueueOverwriteFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xQueueOverwriteFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited. Refer to the Interrupt Service Routines section of the documentation for the port being used to see how that is done.

Returns:

xQueueOverwriteFromISR() is a macro that calls xQueueGenericSendFromISR(), and therefore has the same return values as xQueueSendToFrontFromISR(). However, pdPASS is the only value that can be returned because xQueueOverwriteFromISR() will write to the queue even when the queue is already full.

QueueHandle_t xQueue;

void vFunction( void *pvParameters )
{
    /* Create a queue to hold one unsigned long value.  It is strongly
    recommended not to use xQueueOverwriteFromISR() on queues that can
    contain more than one value, and doing so will trigger an assertion
    if configASSERT() is defined. */
    xQueue = xQueueCreate( 1, sizeof( unsigned long ) );
}

void vAnInterruptHandler( void )
{
/* xHigherPriorityTaskWoken must be set to pdFALSE before it is used. */
BaseType_t xHigherPriorityTaskWoken = pdFALSE;
unsigned long ulVarToSend, ulValReceived;

    /* Write the value 10 to the queue using xQueueOverwriteFromISR(). */
    ulVarToSend = 10;
    xQueueOverwriteFromISR( xQueue, &ulVarToSend, &xHigherPriorityTaskWoken );

    /* The queue is full, but calling xQueueOverwriteFromISR() again will still
    pass because the value held in the queue will be overwritten with the
    new value. */
    ulVarToSend = 100;
    xQueueOverwriteFromISR( xQueue, &ulVarToSend, &xHigherPriorityTaskWoken );

    /* Reading from the queue will now return 100. */

    /* ... */

    if( xHigherPrioritytaskWoken == pdTRUE )
    {
        /* Writing to the queue caused a task to unblock and the unblocked task
        has a priority higher than or equal to the priority of the currently
        executing task (the task this interrupt interrupted).  Perform a
        context switch so this interrupt returns directly to the unblocked
        task. */
        portYIELD_FROM_ISR(); /* or portEND_SWITCHING_ISR() depending on the
        port.*/
    }
}