queue.h

FreeRTOS source code as bundled with the book "Using FreeRTOS Real-Time Kernel - A Practical Approac

 {
    portCHAR ucMessageID;
    portCHAR ucData[ 20 ];
 } xMessage;

 unsigned portLONG ulVar = 10UL;

 void vATask( void *pvParameters )
 {
 xQueueHandle xQueue1, xQueue2;
 struct AMessage *pxMessage;

    // Create a queue capable of containing 10 unsigned long values.
    xQueue1 = xQueueCreate( 10, sizeof( unsigned portLONG ) );

    // 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 unsigned long.  Wait for 10 ticks for space to become
        // available if necessary.
        if( xQueueGenericSend( xQueue1, ( void * ) &ulVar, ( portTickType ) 10, queueSEND_TO_BACK ) != 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;
        xQueueGenericSend( xQueue2, ( void * ) &pxMessage, ( portTickType ) 0, queueSEND_TO_BACK );
    }

	// ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueSend xQueueSend
 * \ingroup QueueManagement
 */
signed portBASE_TYPE xQueueGenericSend( xQueueHandle xQueue, const void * const pvItemToQueue, portTickType xTicksToWait, portBASE_TYPE xCopyPosition );

/**
 * queue. h
 * <pre>
 portBASE_TYPE xQueuePeek(
                             xQueueHandle xQueue,
                             void *pvBuffer,
                             portTickType xTicksToWait
                         );</pre>
 *
 * This is a macro that calls the xQueueGenericReceive() function.
 *
 * Receive an item from a queue without removing the item from the 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.
 *
 * Successfully received items remain on the queue so will be returned again
 * by the next call, or a call to xQueueReceive().
 *
 * This macro must not be used in an interrupt service routine.
 *
 * @param pxQueue The handle to the queue from which the item is to be
 * received.
 *
 * @param pvBuffer Pointer to the buffer into which the received item will
 * be copied.
 *
 * @param 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.    The time is defined in tick periods so the constant
 * portTICK_RATE_MS should be used to convert to real time if this is required.
 *
 * @return pdTRUE if an item was successfully received from the queue,
 * otherwise pdFALSE.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    portCHAR ucMessageID;
    portCHAR ucData[ 20 ];
 } xMessage;

 xQueueHandle 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, ( portTickType ) 0 );

	// ... Rest of task code.
 }

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

    if( xQueue != 0 )
    {
        // Peek a message on the created queue.  Block for 10 ticks if a
        // message is not immediately available.
        if( xQueuePeek( xQueue, &( pxRxedMessage ), ( portTickType ) 10 ) )
        {
            // pcRxedMessage now points to the struct AMessage variable posted
            // by vATask, but the item still remains on the queue.
        }
    }

	// ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueReceive xQueueReceive
 * \ingroup QueueManagement
 */
#define xQueuePeek( xQueue, pvBuffer, xTicksToWait ) xQueueGenericReceive( xQueue, pvBuffer, xTicksToWait, pdTRUE )

/**
 * queue. h
 * <pre>
 portBASE_TYPE xQueueReceive(
                                 xQueueHandle xQueue,
                                 void *pvBuffer,
                                 portTickType xTicksToWait
                            );</pre>
 *
 * 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.
 *
 * Successfully received items are removed from the queue.
 *
 * This function must not be used in an interrupt service routine.  See
 * xQueueReceiveFromISR for an alternative that can.
 *
 * @param pxQueue The handle to the queue from which the item is to be
 * received.
 *
 * @param pvBuffer Pointer to the buffer into which the received item will
 * be copied.
 *
 * @param 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.    The time is defined in tick periods so the constant
 * portTICK_RATE_MS should be used to convert to real time if this is required.
 *
 * @return pdTRUE if an item was successfully received from the queue,
 * otherwise pdFALSE.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    portCHAR ucMessageID;
    portCHAR ucData[ 20 ];
 } xMessage;

 xQueueHandle 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, ( portTickType ) 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 ), ( portTickType ) 10 ) )
        {
            // pcRxedMessage now points to the struct AMessage variable posted
            // by vATask.
        }
    }

	// ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueReceive xQueueReceive
 * \ingroup QueueManagement
 */
#define xQueueReceive( xQueue, pvBuffer, xTicksToWait ) xQueueGenericReceive( xQueue, pvBuffer, xTicksToWait, pdFALSE )


/**
 * queue. h
 * <pre>
 portBASE_TYPE xQueueGenericReceive(
                                       xQueueHandle xQueue,
                                       void *pvBuffer,
                                       portTickType xTicksToWait
                                       portBASE_TYPE xJustPeek
                                    );</pre>
 *
 * It is preferred that the macro xQueueReceive() be used rather than calling
 * this function directly.
 *
 * 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.
 *
 * @param pxQueue The handle to the queue from which the item is to be
 * received.
 *
 * @param pvBuffer Pointer to the buffer into which the received item will
 * be copied.
 *
 * @param 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.    The time is defined in tick periods so the constant
 * portTICK_RATE_MS should be used to convert to real time if this is required.
 *
 * @param xJustPeek When set to true, the item received from the queue is not
 * actually removed from the queue - meaning a subsequent call to
 * xQueueReceive() will return the same item.  When set to false, the item
 * being received from the queue is also removed from the queue.
 *
 * @return pdTRUE if an item was successfully received from the queue,
 * otherwise pdFALSE.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    portCHAR ucMessageID;
    portCHAR ucData[ 20 ];
 } xMessage;

 xQueueHandle 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, ( portTickType ) 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( xQueueGenericReceive( xQueue, &( pxRxedMessage ), ( portTickType ) 10 ) )
        {
            // pcRxedMessage now points to the struct AMessage variable posted
            // by vATask.
        }
    }

	// ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueReceive xQueueReceive
 * \ingroup QueueManagement
 */
signed portBASE_TYPE xQueueGenericReceive( xQueueHandle xQueue, void * const pvBuffer, portTickType xTicksToWait, portBASE_TYPE xJustPeek );

/**
 * queue. h
 * <pre>unsigned portBASE_TYPE uxQueueMessagesWaiting( const xQueueHandle xQueue );</pre>
 *
 * Return the number of messages stored in a queue.
 *
 * @param xQueue A handle to the queue being queried.
 *
 * @return The number of messages available in the queue.
 *
 * \page uxQueueMessagesWaiting uxQueueMessagesWaiting
 * \ingroup QueueManagement
 */
unsigned portBASE_TYPE uxQueueMessagesWaiting( const xQueueHandle xQueue );

/**
 * queue. h
 * <pre>void vQueueDelete( xQueueHandle xQueue );</pre>
 *
 * Delete a queue - freeing all the memory allocated for storing of items
 * placed on the queue.
 *
 * @param xQueue A handle to the queue to be deleted.
 *
 * \page vQueueDelete vQueueDelete
 * \ingroup QueueManagement
 */
void vQueueDelete( xQueueHandle xQueue );

/**
 * queue. h
 * <pre>
 portBASE_TYPE xQueueSendToFrontFromISR(
                                         xQueueHandle pxQueue,
                                         const void *pvItemToQueue,
                                         portBASE_TYPE *pxHigherPriorityTaskWoken
                                      );
 </pre>
 *
 * 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.
 *
 * @param xQueue The handle to the queue on which the item is to be posted.
 *
 * @param 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.
 *
 * @param pxHigherPriorityTaskWoken xQueueSendToFrontFromISR() will set
 * *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task
 * to unblock, and the unblocked task has a priority higher than the currently
 * running task.  If xQueueSendToFromFromISR() sets this value to pdTRUE then
 * a context switch should be requested before the interrupt is exited.
 *
 * @return pdTRUE if the data was successfully sent to the queue, otherwise
 * errQUEUE_FULL.
 *
 * Example usage for buffered IO (where the ISR can obtain more than one value
 * per call):
   <pre>
 void vBufferISR( void )
 {
 portCHAR cIn;
 portBASE_TYPE xHigherPrioritTaskWoken;

    // We have not woken a task at the start of the ISR.
    xHigherPriorityTaskWoken = pdFALSE;

    // Loop until the buffer is empty.
    do
    {
        // Obtain a byte from the buffer.
        cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS );						

        // Post the byte.  
        xQueueSendToFrontFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken );

    } while( portINPUT_BYTE( BUFFER_COUNT ) );

    // Now the buffer is empty we can switch context if necessary.
    if( xHigherPriorityTaskWoken )
    {