Chapter 2. API Reference
(continued from previous page)
// Post the byte.
xQueueSendToBackFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken );
} while( portINPUT_BYTE( BUFFER_COUNT ) );
// Now the buffer is empty we can switch context if necessary.
if( xHigherPriorityTaskWoken )
{
portYIELD_FROM_ISR ();
}
}
Return pdTRUE if the data was successfully sent to the queue, otherwise errQUEUE_FULL.
Parameters
• xQueue: The handle to the queue on which the item is to be posted.
• pvItemToQueue: A pointer to the item that is to be placed on the queue. The size of the items
the queue will hold was defined when the queue was created, so this many bytes will be copied from
pvItemToQueue into the queue storage area.
• [out] pxHigherPriorityTaskWoken: xQueueSendToBackFromISR() will set *pxHigh-
erPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the un-
blocked task has a priority higher than the currently running task. If xQueueSendToBackFromISR()
sets this value to pdTRUE then a context switch should be requested before the interrupt is exited.
xQueueOverwriteFromISR(xQueue, pvItemToQueue, pxHigherPriorityTaskWoken)
A version of xQueueOverwrite() that can be used in an interrupt service routine (ISR).
Only for use with queues that can hold a single item - so the queue is either empty or full.
Post an item on a queue. If the queue is already full then overwrite the value held in the queue. The item is
queued by copy, not by reference.
Example usage:
QueueHandle_t xQueue;
void vFunction( void *pvParameters )
{
// Create a queue to hold one uint32_t 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( uint32_t ) );
}
void vAnInterruptHandler( void )
{
// xHigherPriorityTaskWoken must be set to pdFALSE before it is used.
BaseType_t xHigherPriorityTaskWoken = pdFALSE;
uint32_t 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.
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Espressif Systems 899
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