crQUEUE_RECEIVE is a macro. The data types are shown in the prototype above for reference only.
The macro’s crQUEUE_SEND() and crQUEUE_RECEIVE() are the co-routine
equivalent to the xQueueSend() and xQueueReceive() functions used by tasks.
crQUEUE_SEND and crQUEUE_RECEIVE can only be used from a co-routine whereas
xQueueSend() and xQueueReceive() can only be used from tasks. Note that co-routines
can only send data to other co-routines. A co-routine cannot use a queue to send data to a
task or vice versa.
crQUEUE_RECEIVE can only be called from the co-routine function itself – not
from within a function called by the co-routine function. This is because
co-routines do not maintain their own stack.
See the co-routine section of the web documentation for information on
passing data between tasks and co-routines and between ISR’s and
The handle of the calling co-routine. This is the xHandle parameter of the co-routine function.
The handle of the queue from which the data will be received. The handle is obtained as the return value when the queue is created using the xQueueCreate() API function.
The buffer into which the received item is to be copied. The number of bytes of each queued item is specified when the queue is created. This number of bytes is copied into pvBuffer.
The number of ticks that the co-routine should block to wait for data to become available from the queue, should data not be available immediately. The actual amount of time this equates to is defined by configTICK_RATE_HZ (set in FreeRTOSConfig.h). The constant portTICK_PERIOD_MS can be used to convert ticks to milliseconds (see the crQUEUE_SEND example).
The variable pointed to by pxResult will be set to pdPASS if data was successfully retrieved from the queue, otherwise it will be set to an error code as defined within ProjDefs.h.
// A co-routine receives the number of an LED to flash from a queue. It
// blocks on the queue until the number is received.
static void prvCoRoutineFlashWorkTask( CoRoutineHandle_t xHandle,
UBaseType_t uxIndex )
// Variables in co-routines must be declared static if they must maintain
// value across a blocking call.
static BaseType_t xResult;
static UBaseType_t uxLEDToFlash;
// All co-routines must start with a call to crSTART().
crSTART( xHandle );
for( ;; )
// Wait for data to become available on the queue.
if( xResult == pdPASS )
// We received the LED to flash - flash it!
vParTestToggleLED( uxLEDToFlash );
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