Chapter 2. API Reference
Example usage:
void vFunction( void *pvParameters )
{
QueueHandle_t xQueue;
uint32_t ulVarToSend, ulValReceived;
// Create a queue to hold one uint32_t value. It is strongly
// recommended *not* to use xQueueOverwrite() 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 ) );
// Write the value 10 to the queue using xQueueOverwrite().
ulVarToSend = 10;
xQueueOverwrite( xQueue, &ulVarToSend );
// Peeking the queue should now return 10, but leave the value 10 in
// the queue. A block time of zero is used as it is known that the
// queue holds a value.
ulValReceived = 0;
xQueuePeek( xQueue, &ulValReceived, 0 );
if( ulValReceived != 10 )
{
// Error unless the item was removed by a different task.
}
// The queue is still full. Use xQueueOverwrite() to overwrite the
// value held in the queue with 100.
ulVarToSend = 100;
xQueueOverwrite( xQueue, &ulVarToSend );
// This time read from the queue, leaving the queue empty once more.
// A block time of 0 is used again.
xQueueReceive( xQueue, &ulValReceived, 0 );
// The value read should be the last value written, even though the
// queue was already full when the value was written.
if( ulValReceived != 100 )
{
// Error!
}
// ...
}
Return xQueueOverwrite() is a macro that calls xQueueGenericSend(), and therefore has the same return
values as xQueueSendToFront(). However, pdPASS is the only value that can be returned because
xQueueOverwrite() will write to the queue even when the queue is already full.
Parameters
• xQueue: The handle of the queue to which the data is being sent.
• 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.
xQueueSendToFrontFromISR(xQueue, pvItemToQueue, pxHigherPriorityTaskWoken)
This is a macro that calls xQueueGenericSendFromISR().
Post an item to the front of a queue. It is safe to use this macro from within an interrupt service routine.
Items are queued by copy not reference so it is preferable to only queue small items, especially when called
from an ISR. In most cases it would be preferable to store a pointer to the item being queued.
Espressif Systems 897
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