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[Queue Management]

queue. h
BaseType_t xQueueReceive( QueueHandle_t xQueue, void *pvBuffer, TickType_t xTicksToWait );

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

Receive an item from a queue. The item is received by copy so a buffer of adequate size must be provided. The number of bytes copied into the buffer was defined when the queue was created.

This function must not be used in an interrupt service routine. See xQueueReceiveFromISR for an alternative that can.

xQueue The handle to the queue from which the item is to be received.
pvBuffer Pointer to the buffer into which the received item will be copied.
xTicksToWait The maximum amount of time the task should block waiting for an item to receive should the queue be empty at the time of the call. Setting xTicksToWait to 0 will cause the function to return immediately if the queue is empty. 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.

If INCLUDE_vTaskSuspend is set to ‘1’ then specifying the block time as portMAX_DELAY will cause the task to block indefinitely (without a timeout).

pdTRUE if an item was successfully received from the queue, otherwise pdFALSE.
Example usage:
struct AMessage { char ucMessageID; char ucData[ 20 ]; } xMessage;

QueueHandle_t xQueue;

// Task to create a queue and post a value. void vATask( void *pvParameters ) { struct AMessage *pxMessage;

// Create a queue capable of containing 10 pointers to AMessage structures. // These should be passed by pointer as they contain a lot of data. xQueue = xQueueCreate( 10, sizeof( struct AMessage * ) ); if( xQueue == 0 ) { // Failed to create the queue. }

// ...

// Send a pointer to a struct AMessage object. Don't block if the // queue is already full. pxMessage = & xMessage; xQueueSend( xQueue, ( void * ) &pxMessage, ( TickType_t ) 0 );

// ... Rest of task code. }

// Task to receive from the queue. void vADifferentTask( void *pvParameters ) { struct AMessage *pxRxedMessage;

if( xQueue != 0 ) { // Receive a message on the created queue. Block for 10 ticks if a // message is not immediately available. if( xQueueReceive( xQueue, &( pxRxedMessage ), ( TickType_t ) 10 ) ) { // pcRxedMessage now points to the struct AMessage variable posted // by vATask. } }

// ... Rest of task code. }

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