Chapter 2. API Reference
struct AMessage
{
char ucMessageID;
char ucData[ 20 ];
} xMessage;
uint32_t ulVar = 10UL;
void vATask( void *pvParameters )
{
QueueHandle_t xQueue1, xQueue2;
struct AMessage *pxMessage;
// Create a queue capable of containing 10 uint32_t values.
xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
// Create a queue capable of containing 10 pointers to AMessage structures.
// These should be passed by pointer as they contain a lot of data.
xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );
// ...
if( xQueue1 != 0 )
{
// Send an uint32_t. Wait for 10 ticks for space to become
// available if necessary.
if( xQueueSend( xQueue1, ( void * ) &ulVar, ( TickType_t ) 10 ) != pdPASS␣
,→)
{
// Failed to post the message, even after 10 ticks.
}
}
if( xQueue2 != 0 )
{
// Send a pointer to a struct AMessage object. Don't block if the
// queue is already full.
pxMessage = & xMessage;
xQueueSend( xQueue2, ( void * ) &pxMessage, ( TickType_t ) 0 );
}
// ... Rest of task code.
}
Return pdTRUE if the item was successfully posted, 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.
• xTicksToWait: The maximum amount of time the task should block waiting for space to become
available on the queue, should it already be full. The call will return immediately if this is set to 0
and the queue is full. The time is defined in tick periods so the constant portTICK_PERIOD_MS
should be used to convert to real time if this is required.
xQueueOverwrite(xQueue, pvItemToQueue)
Only for use with queues that have a length of one - 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.
This function must not be called from an interrupt service routine. See xQueueOverwriteFromISR () for an
alternative which may be used in an ISR.
Espressif Systems 896
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