Source/include/queue.h

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*/

#ifndef QUEUE_H
#define QUEUE_H

typedef void * xQueueHandle;

/**
 * queue. h
 * <pre>
 xQueueHandle xQueueCreate( 
                              unsigned portBASE_TYPE uxQueueLength, 
                              unsigned portBASE_TYPE uxItemSize 
                          );
 * </pre>
 *
 * Creates a new queue instance.  This allocates the storage required by the
 * new queue and returns a handle for the queue.
 *
 * @param uxQueueLength The maximum number of items that the queue can contain.
 *
 * @param uxItemSize The number of bytes each item in the queue will require.  
 * Items are queued by copy, not by reference, so this is the number of bytes
 * that will be copied for each posted item.  Each item on the queue must be
 * the same size.
 *
 * @return If the queue is successfully create then a handle to the newly 
 * created queue is returned.  If the queue cannot be created then 0 is
 * returned.
 * 
 * Example usage:
   <pre>
 struct AMessage
 {
    portCHAR ucMessageID;
    portCHAR ucData[ 20 ];
 };

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

    // Create a queue capable of containing 10 unsigned long values.
    xQueue1 = xQueueCreate( 10, sizeof( unsigned portLONG ) );
    if( xQueue1 == 0 )
    {
        // Queue was not created and must not be used.
    }

    // 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( xQueue2 == 0 )
    {
        // Queue was not created and must not be used.
    }

    // ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueCreate xQueueCreate
 * \ingroup QueueManagement
 */
xQueueHandle xQueueCreate( unsigned portBASE_TYPE uxQueueLength, unsigned portBASE_TYPE uxItemSize );

/**
 * queue. h
 * <pre>
 portBASE_TYPE xQueueSend( 
                             xQueueHandle xQueue, 
                             const void * pvItemToQueue, 
                             portTickType xTicksToWait 
                         );
 * </pre>
 *
 * Post an item on a queue.  The item is queued by copy, not by reference.
 * This function must not be called from an interrupt service routine.
 * See xQueueSendFromISR () for an alternative which may be used in an ISR.
 *
 * @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 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.  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 the item was successfully posted, otherwise errQUEUE_FULL.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    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( xQueueSend( xQueue1, ( void * ) &ulVar, ( portTickType ) 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, ( portTickType ) 0 );
    }

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

/**
 * queue. h
 * <pre>
 portBASE_TYPE xQueueReceive( 
                                xQueueHandle xQueue, 
                                void *pvBuffer, 
                                portTickType xTicksToWait 
                            );</pre>
 *
 * 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.
 *
 * @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
 */
signed portBASE_TYPE xQueueReceive( xQueueHandle xQueue, void *pvBuffer, portTickType xTicksToWait );

/**
 * queue. h
 * <pre>unsigned portBASE_TYPE uxQueueMessagesWaiting( 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( 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 xQueueSendFromISR( 
                                    xQueueHandle pxQueue, 
                                    const void *pvItemToQueue, 
                                    portBASE_TYPE xTaskPreviouslyWoken 
                                );
 </pre>
 *
 * Post an item on a queue.  It is safe to use this function 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 cTaskPreviouslyWoken This is included so an ISR can post onto
 * the same queue multiple times from a single interrupt.  The first call
 * should always pass in pdFALSE.  Subsequent calls should pass in
 * the value returned from the previous call.  See the file serial .c in the
 * PC port for a good example of this mechanism.
 *
 * @return pdTRUE if a task was woken by posting onto the queue.  This is 
 * used by the ISR to determine if a context switch may be required following
 * the ISR.
 *
 * Example usage for buffered IO (where the ISR can obtain more than one value
 * per call):
   <pre>
 void vBufferISR( void )
 {
 portCHAR cIn;
 portBASE_TYPE xTaskWokenByPost;

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

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

        // Post the byte.  The first time round the loop cTaskWokenByPost
        // will be pdFALSE.  If the queue send causes a task to wake we do
        // not want the task to run until we have finished the ISR, so
        // xQueueSendFromISR does not cause a context switch.  Also we 
        // don't want subsequent posts to wake any other tasks, so we store
        // the return value back into cTaskWokenByPost so xQueueSendFromISR
        // knows not to wake any task the next iteration of the loop.
        xTaskWokenByPost = xQueueSendFromISR( xRxQueue, &cIn, cTaskWokenByPost );

    } while( portINPUT_BYTE( BUFFER_COUNT ) );

    // Now the buffer is empty we can switch context if necessary.
    if( cTaskWokenByPost )
    {
        taskYIELD ();
    }
 }
 </pre>
 *
 * \defgroup xQueueSendFromISR xQueueSendFromISR
 * \ingroup QueueManagement
 */
signed portBASE_TYPE xQueueSendFromISR( xQueueHandle pxQueue, const void *pvItemToQueue, signed portBASE_TYPE xTaskPreviouslyWoken );

/**
 * queue. h
 * <pre>
 portBASE_TYPE xQueueReceiveFromISR( 
                                       xQueueHandle pxQueue, 
                                       void *pvBuffer, 
                                       portBASE_TYPE *pxTaskWoken 
                                   ); 
 * </pre>
 *
 * Receive an item from a queue.  It is safe to use this function from within 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 pxTaskWoken A task may be blocked waiting for space to become
 * available on the queue.  If xQueueReceiveFromISR causes such a task to
 * unblock *pxTaskWoken will get set to pdTRUE, otherwise *pxTaskWoken will
 * remain unchanged.
 *
 * @return pdTRUE if an item was successfully received from the queue,
 * otherwise pdFALSE.
 *
 * Example usage:
   <pre>
 
 xQueueHandle xQueue;
 
 // Function to create a queue and post some values.
 void vAFunction( void *pvParameters )
 {
 portCHAR cValueToPost;
 const portTickType xBlockTime = ( portTickType )0xff;

    // Create a queue capable of containing 10 characters.
    xQueue = xQueueCreate( 10, sizeof( portCHAR ) );
    if( xQueue == 0 )
    {
        // Failed to create the queue.
    }

    // ...

    // Post some characters that will be used within an ISR.  If the queue
    // is full then this task will block for xBlockTime ticks.
    cValueToPost = 'a';
    xQueueSend( xQueue, ( void * ) &cValueToPost, xBlockTime );
    cValueToPost = 'b';
    xQueueSend( xQueue, ( void * ) &cValueToPost, xBlockTime );

    // ... keep posting characters ... this task may block when the queue
    // becomes full.

    cValueToPost = 'c';
    xQueueSend( xQueue, ( void * ) &cValueToPost, xBlockTime );
 }

 // ISR that outputs all the characters received on the queue. 
 void vISR_Routine( void )
 {
 portBASE_TYPE xTaskWokenByReceive = pdFALSE;
 portCHAR cRxedChar;

    while( xQueueReceiveFromISR( xQueue, ( void * ) &cRxedChar, &xTaskWokenByReceive) )
    {
        // A character was received.  Output the character now.
        vOutputCharacter( cRxedChar );

        // If removing the character from the queue woke the task that was 
        // posting onto the queue cTaskWokenByReceive will have been set to
        // pdTRUE.  No matter how many times this loop iterates only one
        // task will be woken.
    }

    if( cTaskWokenByPost != ( portCHAR ) pdFALSE;
    {
        taskYIELD ();
    }
 }
 </pre>
 * \defgroup xQueueReceiveFromISR xQueueReceiveFromISR
 * \ingroup QueueManagement
 */
signed portBASE_TYPE xQueueReceiveFromISR( xQueueHandle pxQueue, void *pvBuffer, signed portBASE_TYPE *pxTaskWoken );


/* 
 * The functions defined above are for passing data to and from tasks.  The 
 * functions below are the equivalents for passing data to and from 
 * co-rtoutines.
 *
 * These functions are called from the co-routine macro implementation and
 * should not be called directly from application code.  Instead use the macro
 * wrappers defined within croutine.h.
 */
signed portBASE_TYPE xQueueCRSendFromISR( xQueueHandle pxQueue, const void *pvItemToQueue, signed portBASE_TYPE xCoRoutinePreviouslyWoken );
signed portBASE_TYPE xQueueCRReceiveFromISR( xQueueHandle pxQueue, void *pvBuffer, signed portBASE_TYPE *pxTaskWoken );
signed portBASE_TYPE xQueueCRSend( xQueueHandle pxQueue, const void *pvItemToQueue, portTickType xTicksToWait );
signed portBASE_TYPE xQueueCRReceive( xQueueHandle pxQueue, void *pvBuffer, portTickType xTicksToWait );

#endif