root/Examples_CP-JR_ARM7_LPC2368/FreeRTOS_Book/Source-Code-For-Examples/FreeRTOS_Source/queue.c

/*
        FreeRTOS.org V5.0.4 - Copyright (C) 2003-2008 Richard Barry.

        This file is part of the FreeRTOS.org distribution.

        FreeRTOS.org is free software; you can redistribute it and/or modify
        it under the terms of the GNU General Public License as published by
        the Free Software Foundation; either version 2 of the License, or
        (at your option) any later version.

        FreeRTOS.org is distributed in the hope that it will be useful,
        but WITHOUT ANY WARRANTY; without even the implied warranty of
        MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
        GNU General Public License for more details.

        You should have received a copy of the GNU General Public License
        along with FreeRTOS.org; if not, write to the Free Software
        Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

        A special exception to the GPL can be applied should you wish to distribute
        a combined work that includes FreeRTOS.org, without being obliged to provide
        the source code for any proprietary components.  See the licensing section
        of http://www.FreeRTOS.org for full details of how and when the exception
        can be applied.

    ***************************************************************************
    ***************************************************************************
    *                                                                         *
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        Please ensure to read the configuration and relevant port sections of the
        online documentation.

        http://www.FreeRTOS.org - Documentation, latest information, license and
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*/

#include <stdlib.h>
#include <string.h>
#include "FreeRTOS.h"
#include "task.h"
#include "croutine.h"

/*-----------------------------------------------------------
 * PUBLIC LIST API documented in list.h
 *----------------------------------------------------------*/

/* Constants used with the cRxLock and cTxLock structure members. */
#define queueUNLOCKED                                                   ( ( signed portBASE_TYPE ) -1 )
#define queueLOCKED_UNMODIFIED                                  ( ( signed portBASE_TYPE ) 0 )

#define queueERRONEOUS_UNBLOCK                                  ( -1 )

/* For internal use only. */
#define queueSEND_TO_BACK       ( 0 )
#define queueSEND_TO_FRONT      ( 1 )

/* Effectively make a union out of the xQUEUE structure. */
#define pxMutexHolder                           pcTail
#define uxQueueType                                     pcHead
#define uxRecursiveCallCount            pcReadFrom
#define queueQUEUE_IS_MUTEX                     NULL

/* Semaphores do not actually store or copy data, so have an items size of
zero. */
#define queueSEMAPHORE_QUEUE_ITEM_LENGTH ( 0 )
#define queueDONT_BLOCK                                  ( ( portTickType ) 0 )
#define queueMUTEX_GIVE_BLOCK_TIME               ( ( portTickType ) 0 )

/*
 * Definition of the queue used by the scheduler.
 * Items are queued by copy, not reference.
 */
typedef struct QueueDefinition
{
        signed portCHAR *pcHead;                                /*< Points to the beginning of the queue storage area. */
        signed portCHAR *pcTail;                                /*< Points to the byte at the end of the queue storage area.  Once more byte is allocated than necessary to store the queue items, this is used as a marker. */

        signed portCHAR *pcWriteTo;                             /*< Points to the free next place in the storage area. */
        signed portCHAR *pcReadFrom;                    /*< Points to the last place that a queued item was read from. */

        xList xTasksWaitingToSend;                              /*< List of tasks that are blocked waiting to post onto this queue.  Stored in priority order. */
        xList xTasksWaitingToReceive;                   /*< List of tasks that are blocked waiting to read from this queue.  Stored in priority order. */

        volatile unsigned portBASE_TYPE uxMessagesWaiting;/*< The number of items currently in the queue. */
        unsigned portBASE_TYPE uxLength;                /*< The length of the queue defined as the number of items it will hold, not the number of bytes. */
        unsigned portBASE_TYPE uxItemSize;              /*< The size of each items that the queue will hold. */

        signed portBASE_TYPE xRxLock;                   /*< Stores the number of items received from the queue (removed from the queue) while the queue was locked.  Set to queueUNLOCKED when the queue is not locked. */
        signed portBASE_TYPE xTxLock;                   /*< Stores the number of items transmitted to the queue (added to the queue) while the queue was locked.  Set to queueUNLOCKED when the queue is not locked. */

} xQUEUE;
/*-----------------------------------------------------------*/

/*
 * Inside this file xQueueHandle is a pointer to a xQUEUE structure.
 * To keep the definition private the API header file defines it as a
 * pointer to void.
 */
typedef xQUEUE * xQueueHandle;

/*
 * Prototypes for public functions are included here so we don't have to
 * include the API header file (as it defines xQueueHandle differently).  These
 * functions are documented in the API header file.
 */
xQueueHandle xQueueCreate( unsigned portBASE_TYPE uxQueueLength, unsigned portBASE_TYPE uxItemSize );
signed portBASE_TYPE xQueueGenericSend( xQueueHandle xQueue, const void * const pvItemToQueue, portTickType xTicksToWait, portBASE_TYPE xCopyPosition );
unsigned portBASE_TYPE uxQueueMessagesWaiting( const xQueueHandle pxQueue );
void vQueueDelete( xQueueHandle xQueue );
signed portBASE_TYPE xQueueGenericSendFromISR( xQueueHandle pxQueue, const void * const pvItemToQueue, signed portBASE_TYPE *pxHigherPriorityTaskWoken, portBASE_TYPE xCopyPosition );
signed portBASE_TYPE xQueueGenericReceive( xQueueHandle pxQueue, void * const pvBuffer, portTickType xTicksToWait, portBASE_TYPE xJustPeeking );
signed portBASE_TYPE xQueueReceiveFromISR( xQueueHandle pxQueue, void * const pvBuffer, signed portBASE_TYPE *pxTaskWoken );
xQueueHandle xQueueCreateMutex( void );
xQueueHandle xQueueCreateCountingSemaphore( unsigned portBASE_TYPE uxCountValue, unsigned portBASE_TYPE uxInitialCount );
portBASE_TYPE xQueueTakeMutexRecursive( xQueueHandle xMutex, portTickType xBlockTime );
portBASE_TYPE xQueueGiveMutexRecursive( xQueueHandle xMutex );
signed portBASE_TYPE xQueueAltGenericSend( xQueueHandle pxQueue, const void * const pvItemToQueue, portTickType xTicksToWait, portBASE_TYPE xCopyPosition );
signed portBASE_TYPE xQueueAltGenericReceive( xQueueHandle pxQueue, void * const pvBuffer, portTickType xTicksToWait, portBASE_TYPE xJustPeeking );
signed portBASE_TYPE xQueueIsQueueEmptyFromISR( const xQueueHandle pxQueue );
signed portBASE_TYPE xQueueIsQueueFullFromISR( const xQueueHandle pxQueue );
unsigned portBASE_TYPE uxQueueMessagesWaitingFromISR( const xQueueHandle pxQueue );

/*
 * Co-routine queue functions differ from task queue functions.  Co-routines are
 * an optional component.
 */
#if configUSE_CO_ROUTINES == 1
        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

/*
 * The queue registry is just a means for kernel aware debuggers to locate
 * queue structures.  It has no other purpose so is an optional component.
 */
#if configQUEUE_REGISTRY_SIZE > 0

        /* The type stored within the queue registry array.  This allows a name
        to be assigned to each queue making kernel aware debugging a little
        more user friendly. */
        typedef struct QUEUE_REGISTRY_ITEM
        {
                signed portCHAR *pcQueueName;
                xQueueHandle xHandle;
        } xQueueRegistryItem;

        /* The queue registry is simply an array of xQueueRegistryItem structures.
        The pcQueueName member of a structure being NULL is indicative of the
        array position being vacant. */
        xQueueRegistryItem xQueueRegistry[ configQUEUE_REGISTRY_SIZE ];

        /* Removes a queue from the registry by simply setting the pcQueueName
        member to NULL. */
        static void vQueueUnregisterQueue( xQueueHandle xQueue );
        void vQueueAddToRegistry( xQueueHandle xQueue, signed portCHAR *pcQueueName );
#endif

/*
 * Unlocks a queue locked by a call to prvLockQueue.  Locking a queue does not
 * prevent an ISR from adding or removing items to the queue, but does prevent
 * an ISR from removing tasks from the queue event lists.  If an ISR finds a
 * queue is locked it will instead increment the appropriate queue lock count
 * to indicate that a task may require unblocking.  When the queue in unlocked
 * these lock counts are inspected, and the appropriate action taken.
 */
static void prvUnlockQueue( xQueueHandle pxQueue );

/*
 * Uses a critical section to determine if there is any data in a queue.
 *
 * @return pdTRUE if the queue contains no items, otherwise pdFALSE.
 */
static signed portBASE_TYPE prvIsQueueEmpty( const xQueueHandle pxQueue );

/*
 * Uses a critical section to determine if there is any space in a queue.
 *
 * @return pdTRUE if there is no space, otherwise pdFALSE;
 */
static signed portBASE_TYPE prvIsQueueFull( const xQueueHandle pxQueue );

/*
 * Copies an item into the queue, either at the front of the queue or the
 * back of the queue.
 */
static void prvCopyDataToQueue( xQUEUE *pxQueue, const void *pvItemToQueue, portBASE_TYPE xPosition );

/*
 * Copies an item out of a queue.
 */
static void prvCopyDataFromQueue( xQUEUE * const pxQueue, const void *pvBuffer );
/*-----------------------------------------------------------*/

/*
 * Macro to mark a queue as locked.  Locking a queue prevents an ISR from
 * accessing the queue event lists.
 */
#define prvLockQueue( pxQueue )                                                 \
{                                                                                                               \
        taskENTER_CRITICAL();                                                           \
        {                                                                                                       \
                if( pxQueue->xRxLock == queueUNLOCKED )                 \
                {                                                                                               \
                        pxQueue->xRxLock = queueLOCKED_UNMODIFIED;      \
                }                                                                                               \
                if( pxQueue->xTxLock == queueUNLOCKED )                 \
                {                                                                                               \
                        pxQueue->xTxLock = queueLOCKED_UNMODIFIED;      \
                }                                                                                               \
        }                                                                                                       \
        taskEXIT_CRITICAL();                                                            \
}
/*-----------------------------------------------------------*/


/*-----------------------------------------------------------
 * PUBLIC QUEUE MANAGEMENT API documented in queue.h
 *----------------------------------------------------------*/

xQueueHandle xQueueCreate( unsigned portBASE_TYPE uxQueueLength, unsigned portBASE_TYPE uxItemSize )
{
xQUEUE *pxNewQueue;
size_t xQueueSizeInBytes;

        /* Allocate the new queue structure. */
        if( uxQueueLength > ( unsigned portBASE_TYPE ) 0 )
        {
                pxNewQueue = ( xQUEUE * ) pvPortMalloc( sizeof( xQUEUE ) );
                if( pxNewQueue != NULL )
                {
                        /* Create the list of pointers to queue items.  The queue is one byte
                        longer than asked for to make wrap checking easier/faster. */
                        xQueueSizeInBytes = ( size_t ) ( uxQueueLength * uxItemSize ) + ( size_t ) 1;

                        pxNewQueue->pcHead = ( signed portCHAR * ) pvPortMalloc( xQueueSizeInBytes );
                        if( pxNewQueue->pcHead != NULL )
                        {
                                /* Initialise the queue members as described above where the
                                queue type is defined. */
                                pxNewQueue->pcTail = pxNewQueue->pcHead + ( uxQueueLength * uxItemSize );
                                pxNewQueue->uxMessagesWaiting = 0;
                                pxNewQueue->pcWriteTo = pxNewQueue->pcHead;
                                pxNewQueue->pcReadFrom = pxNewQueue->pcHead + ( ( uxQueueLength - 1 ) * uxItemSize );
                                pxNewQueue->uxLength = uxQueueLength;
                                pxNewQueue->uxItemSize = uxItemSize;
                                pxNewQueue->xRxLock = queueUNLOCKED;
                                pxNewQueue->xTxLock = queueUNLOCKED;

                                /* Likewise ensure the event queues start with the correct state. */
                                vListInitialise( &( pxNewQueue->xTasksWaitingToSend ) );
                                vListInitialise( &( pxNewQueue->xTasksWaitingToReceive ) );

                                traceQUEUE_CREATE( pxNewQueue );

                                return  pxNewQueue;
                        }
                        else
                        {
                                traceQUEUE_CREATE_FAILED();
                                vPortFree( pxNewQueue );
                        }
                }
        }

        /* Will only reach here if we could not allocate enough memory or no memory
        was required. */
        return NULL;
}
/*-----------------------------------------------------------*/

#if ( configUSE_MUTEXES == 1 )

        xQueueHandle xQueueCreateMutex( void )
        {
        xQUEUE *pxNewQueue;

                /* Allocate the new queue structure. */
                pxNewQueue = ( xQUEUE * ) pvPortMalloc( sizeof( xQUEUE ) );
                if( pxNewQueue != NULL )
                {
                        /* Information required for priority inheritance. */
                        pxNewQueue->pxMutexHolder = NULL;
                        pxNewQueue->uxQueueType = queueQUEUE_IS_MUTEX;

                        /* Queues used as a mutex no data is actually copied into or out
                        of the queue. */
                        pxNewQueue->pcWriteTo = NULL;
                        pxNewQueue->pcReadFrom = NULL;

                        /* Each mutex has a length of 1 (like a binary semaphore) and
                        an item size of 0 as nothing is actually copied into or out
                        of the mutex. */
                        pxNewQueue->uxMessagesWaiting = 0;
                        pxNewQueue->uxLength = 1;
                        pxNewQueue->uxItemSize = 0;
                        pxNewQueue->xRxLock = queueUNLOCKED;
                        pxNewQueue->xTxLock = queueUNLOCKED;

                        /* Ensure the event queues start with the correct state. */
                        vListInitialise( &( pxNewQueue->xTasksWaitingToSend ) );
                        vListInitialise( &( pxNewQueue->xTasksWaitingToReceive ) );

                        /* Start with the semaphore in the expected state. */
                        xQueueGenericSend( pxNewQueue, NULL, 0, queueSEND_TO_BACK );

                        traceCREATE_MUTEX( pxNewQueue );
                }
                else
                {
                        traceCREATE_MUTEX_FAILED();
                }

                return pxNewQueue;
        }

#endif /* configUSE_MUTEXES */
/*-----------------------------------------------------------*/

#if configUSE_RECURSIVE_MUTEXES == 1

        portBASE_TYPE xQueueGiveMutexRecursive( xQueueHandle pxMutex )
        {
        portBASE_TYPE xReturn;

                /* If this is the task that holds the mutex then pxMutexHolder will not
                change outside of this task.  If this task does not hold the mutex then
                pxMutexHolder can never coincidentally equal the tasks handle, and as
                this is the only condition we are interested in it does not matter if
                pxMutexHolder is accessed simultaneously by another task.  Therefore no
                mutual exclusion is required to test the pxMutexHolder variable. */
                if( pxMutex->pxMutexHolder == xTaskGetCurrentTaskHandle() )
                {
                        traceGIVE_MUTEX_RECURSIVE( pxMutex );

                        /* uxRecursiveCallCount cannot be zero if pxMutexHolder is equal to
                        the task handle, therefore no underflow check is required.  Also,
                        uxRecursiveCallCount is only modified by the mutex holder, and as
                        there can only be one, no mutual exclusion is required to modify the
                        uxRecursiveCallCount member. */
                        ( pxMutex->uxRecursiveCallCount )--;

                        /* Have we unwound the call count? */
                        if( pxMutex->uxRecursiveCallCount == 0 )
                        {
                                /* Return the mutex.  This will automatically unblock any other
                                task that might be waiting to access the mutex. */
                xQueueGenericSend( pxMutex, NULL, queueMUTEX_GIVE_BLOCK_TIME, queueSEND_TO_BACK );
                        }

                        xReturn = pdPASS;
                }
                else
                {
                        /* We cannot give the mutex because we are not the holder. */
                        xReturn = pdFAIL;

                        traceGIVE_MUTEX_RECURSIVE_FAILED( pxMutex );
                }

                return xReturn;
        }

#endif /* configUSE_RECURSIVE_MUTEXES */
/*-----------------------------------------------------------*/

#if configUSE_RECURSIVE_MUTEXES == 1

        portBASE_TYPE xQueueTakeMutexRecursive( xQueueHandle pxMutex, portTickType xBlockTime )
        {
        portBASE_TYPE xReturn;

                /* Comments regarding mutual exclusion as per those within
                xQueueGiveMutexRecursive(). */

                traceTAKE_MUTEX_RECURSIVE( pxMutex );

                if( pxMutex->pxMutexHolder == xTaskGetCurrentTaskHandle() )
                {
                        ( pxMutex->uxRecursiveCallCount )++;
                        xReturn = pdPASS;
                }
                else
                {
            xReturn = xQueueGenericReceive( pxMutex, NULL, xBlockTime, pdFALSE );

                        /* pdPASS will only be returned if we successfully obtained the mutex,
                        we may have blocked to reach here. */
                        if( xReturn == pdPASS )
                        {
                                ( pxMutex->uxRecursiveCallCount )++;
                        }
                }

                return xReturn;
        }

#endif /* configUSE_RECURSIVE_MUTEXES */
/*-----------------------------------------------------------*/

#if configUSE_COUNTING_SEMAPHORES == 1

        xQueueHandle xQueueCreateCountingSemaphore( unsigned portBASE_TYPE uxCountValue, unsigned portBASE_TYPE uxInitialCount )
        {
        xQueueHandle pxHandle;

                pxHandle = xQueueCreate( ( unsigned portBASE_TYPE ) uxCountValue, queueSEMAPHORE_QUEUE_ITEM_LENGTH );

                if( pxHandle != NULL )
                {
                        pxHandle->uxMessagesWaiting = uxInitialCount;

                        traceCREATE_COUNTING_SEMAPHORE();
                }
                else
                {
                        traceCREATE_COUNTING_SEMAPHORE_FAILED();
                }

                return pxHandle;
        }

#endif /* configUSE_COUNTING_SEMAPHORES */
/*-----------------------------------------------------------*/

signed portBASE_TYPE xQueueGenericSend( xQueueHandle pxQueue, const void * const pvItemToQueue, portTickType xTicksToWait, portBASE_TYPE xCopyPosition )
{
signed portBASE_TYPE xReturn = pdTRUE;
xTimeOutType xTimeOut;

        do
        {
        /* If xTicksToWait is zero then we are not going to block even
        if there is no room in the queue to post. */
                if( xTicksToWait > ( portTickType ) 0 )
                {
                        vTaskSuspendAll();
                        prvLockQueue( pxQueue );

                        if( xReturn == pdTRUE )
                        {
                                /* This is the first time through - we need to capture the
                                time while the scheduler is locked to ensure we attempt to
                                block at least once. */
                                vTaskSetTimeOutState( &xTimeOut );
                        }

                        if( prvIsQueueFull( pxQueue ) )
                        {
                        /* Need to call xTaskCheckForTimeout again as time could
                        have passed since it was last called if this is not the
                        first time around this loop.  */
                                if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
                                {
                                        traceBLOCKING_ON_QUEUE_SEND( pxQueue );
                                        vTaskPlaceOnEventList( &( pxQueue->xTasksWaitingToSend ), xTicksToWait );

                                        /* Unlocking the queue means queue events can effect the
                                        event list.  It is possible     that interrupts occurring now
                                        remove this task from the event list again - but as the
                                        scheduler is suspended the task will go onto the pending
                                        ready last instead of the actual ready list. */
                                        prvUnlockQueue( pxQueue );

                                        /* Resuming the scheduler will move tasks from the pending
                                        ready list into the ready list - so it is feasible that this
                                        task is already in a ready list before it yields - in which
                                        case the yield will not cause a context switch unless there
                                        is also a higher priority task in the pending ready list. */
                                        if( !xTaskResumeAll() )
                                        {
                                                taskYIELD();
                                        }
                                }
                                else
                                {
                                        prvUnlockQueue( pxQueue );
                                        ( void ) xTaskResumeAll();
                                }
                        }
                        else
                        {
                        /* The queue was not full so we can just unlock the
                        scheduler and queue again before carrying on. */
                                prvUnlockQueue( pxQueue );
                                ( void ) xTaskResumeAll();
                        }
                }

                /* Higher priority tasks and interrupts can execute during
                this time and could possible refill the queue - even if we
                unblocked because space became available. */

                taskENTER_CRITICAL();
                {
                        /* Is there room on the queue now?  To be running we must be
                        the highest priority task wanting to access the queue. */
                        if( pxQueue->uxMessagesWaiting < pxQueue->uxLength )
                        {
                                traceQUEUE_SEND( pxQueue );
                                prvCopyDataToQueue( pxQueue, pvItemToQueue, xCopyPosition );
                                xReturn = pdPASS;

                                /* If there was a task waiting for data to arrive on the
                                queue then unblock it now. */
                                if( listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) == pdFALSE )
                                {
                                        if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) == pdTRUE )
                                        {
                                            /* The unblocked task has a priority higher than
                                            our own so yield immediately. */
                                            taskYIELD();
                                        }
                                }
                        }
                        else
                        {
                                /* Setting xReturn to errQUEUE_FULL will force its timeout
                                to be re-evaluated.  This is necessary in case interrupts
                                and higher priority tasks accessed the queue between this
                                task being unblocked and subsequently attempting to write
                                to the queue. */
                                xReturn = errQUEUE_FULL;
                        }
                }
                taskEXIT_CRITICAL();

                if( xReturn == errQUEUE_FULL )
                {
                        if( xTicksToWait > ( portTickType ) 0 )
                        {
                                if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
                                {
                                        xReturn = queueERRONEOUS_UNBLOCK;
                                }
                                else
                                {
                                        traceQUEUE_SEND_FAILED( pxQueue );
                                }
                        }
                        else
                        {
                                traceQUEUE_SEND_FAILED( pxQueue );
                        }
                }
        }
        while( xReturn == queueERRONEOUS_UNBLOCK );

        return xReturn;
}
/*-----------------------------------------------------------*/

#if configUSE_ALTERNATIVE_API == 1

        signed portBASE_TYPE xQueueAltGenericSend( xQueueHandle pxQueue, const void * const pvItemToQueue, portTickType xTicksToWait, portBASE_TYPE xCopyPosition )
        {
        signed portBASE_TYPE xReturn = pdPASS;
        xTimeOutType xTimeOut;

                /* The source code that implements the alternative (Alt) API is
                simpler because it makes more use of critical sections.  This is
                the approach taken by many other RTOSes, but FreeRTOS.org has the
                preferred fully featured API too.  The fully featured API has more
                complex code that takes longer to execute, but makes less use of
                critical sections.  */

                do
                {
                /* If xTicksToWait is zero then we are not going to block even
                if there is no room in the queue to post. */
                        if( xTicksToWait > ( portTickType ) 0 )
                        {
                                portENTER_CRITICAL();
                                {
                                        if( xReturn == pdPASS )
                                        {
                                                /* This is the first time through - capture the time
                                                inside the critical section to ensure we attempt to
                                                block at least once. */
                                                vTaskSetTimeOutState( &xTimeOut );
                                        }

                                        if( prvIsQueueFull( pxQueue ) )
                                        {
                                        /* Need to call xTaskCheckForTimeout again as time could
                                        have passed since it was last called if this is not the
                                        first time around this loop.  */
                                                if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
                                                {
                                                        traceBLOCKING_ON_QUEUE_SEND( pxQueue );
                                                        vTaskPlaceOnEventList( &( pxQueue->xTasksWaitingToSend ), xTicksToWait );

                                                        /* This will exit the critical section, then re-enter when
                                                        the task next runs. */
                                                        taskYIELD();
                                                }
                                        }
                                }
                                portEXIT_CRITICAL();
                        }

                        /* Higher priority tasks and interrupts can execute during
                        this time and could possible refill the queue - even if we
                        unblocked because space became available. */

                        taskENTER_CRITICAL();
                        {
                                /* Is there room on the queue now?  To be running we must be
                                the highest priority task wanting to access the queue. */
                                if( pxQueue->uxMessagesWaiting < pxQueue->uxLength )
                                {
                                        traceQUEUE_SEND( pxQueue );
                                        prvCopyDataToQueue( pxQueue, pvItemToQueue, xCopyPosition );
                                        xReturn = pdPASS;

                                        /* If there was a task waiting for data to arrive on the
                                        queue then unblock it now. */
                                        if( listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) == pdFALSE )
                                        {
                                                if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) == pdTRUE )
                                                {
                                                        /* The unblocked task has a priority higher than
                                                        our own so yield immediately. */
                                                        taskYIELD();
                                                }
                                        }
                                }
                                else
                                {
                                        /* Setting xReturn to errQUEUE_FULL will force its timeout
                                        to be re-evaluated.  This is necessary in case interrupts
                                        and higher priority tasks accessed the queue between this
                                        task being unblocked and subsequently attempting to write
                                        to the queue. */
                                        xReturn = errQUEUE_FULL;
                                }
                        }
                        taskEXIT_CRITICAL();

                        if( xReturn == errQUEUE_FULL )
                        {
                                if( xTicksToWait > ( portTickType ) 0 )
                                {
                                        if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
                                        {
                                                xReturn = queueERRONEOUS_UNBLOCK;
                                        }
                                        else
                                        {
                                                traceQUEUE_SEND_FAILED( pxQueue );
                                        }
                                }
                                else
                                {
                                        traceQUEUE_SEND_FAILED( pxQueue );
                                }
                        }
                }
                while( xReturn == queueERRONEOUS_UNBLOCK );

                return xReturn;
        }

#endif /* configUSE_ALTERNATIVE_API */
/*-----------------------------------------------------------*/

#if configUSE_ALTERNATIVE_API == 1

        signed portBASE_TYPE xQueueAltGenericReceive( xQueueHandle pxQueue, void * const pvBuffer, portTickType xTicksToWait, portBASE_TYPE xJustPeeking )
        {
        signed portBASE_TYPE xReturn = pdTRUE;
        xTimeOutType xTimeOut;
        signed portCHAR *pcOriginalReadPosition;

                /* The source code that implements the alternative (Alt) API is
                simpler because it makes more use of critical sections.  This is
                the approach taken by many other RTOSes, but FreeRTOS.org has the
                preferred fully featured API too.  The fully featured API has more
                complex code that takes longer to execute, but makes less use of
                critical sections.  */

                do
                {
                        /* If there are no messages in the queue we may have to block. */
                        if( xTicksToWait > ( portTickType ) 0 )
                        {
                                portENTER_CRITICAL();
                                {
                                        if( xReturn == pdPASS )
                                        {
                                                /* This is the first time through - capture the time
                                                inside the critical section to ensure we attempt to
                                                block at least once. */
                                                vTaskSetTimeOutState( &xTimeOut );
                                        }

                                        if( prvIsQueueEmpty( pxQueue ) )
                                        {
                                        /* Need to call xTaskCheckForTimeout again as time could
                                        have passed since it was last called if this is not the
                                        first time around this loop. */
                                                if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
                                                {
                                                        traceBLOCKING_ON_QUEUE_RECEIVE( pxQueue );

                                                        #if ( configUSE_MUTEXES == 1 )
                                                        {
                                                                if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
                                                                {
                                                                        vTaskPriorityInherit( ( void * ) pxQueue->pxMutexHolder );
                                                                }
                                                        }
                                                        #endif

                                                        vTaskPlaceOnEventList( &( pxQueue->xTasksWaitingToReceive ), xTicksToWait );
                                                        taskYIELD();
                                                }
                                        }
                                }
                                portEXIT_CRITICAL();
                        }

                        taskENTER_CRITICAL();
                        {
                                if( pxQueue->uxMessagesWaiting > ( unsigned portBASE_TYPE ) 0 )
                                {
                                        /* Remember our read position in case we are just peeking. */
                                        pcOriginalReadPosition = pxQueue->pcReadFrom;

                                        prvCopyDataFromQueue( pxQueue, pvBuffer );

                                        if( xJustPeeking == pdFALSE )
                                        {
                                                traceQUEUE_RECEIVE( pxQueue );

                                                /* We are actually removing data. */
                                                --( pxQueue->uxMessagesWaiting );

                                                #if ( configUSE_MUTEXES == 1 )
                                                {
                                                        if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
                                                        {
                                                                /* Record the information required to implement
                                                                priority inheritance should it become necessary. */
                                                                pxQueue->pxMutexHolder = xTaskGetCurrentTaskHandle();
                                                        }
                                                }
                                                #endif

                                                if( listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) == pdFALSE )
                                                {
                                                        if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) == pdTRUE )
                                                        {
                                                                taskYIELD();
                                                        }
                                                }
                                        }
                                        else
                                        {
                                                traceQUEUE_PEEK( pxQueue );

                                                /* We are not removing the data, so reset our read
                                                pointer. */
                                                pxQueue->pcReadFrom = pcOriginalReadPosition;

                                                /* The data is being left in the queue, so see if there are
                                                any other tasks waiting for the data. */
                                                if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) )
                                                {
                                                        /* Tasks that are removed from the event list will get added to
                                                        the pending ready list as the scheduler is still suspended. */
                                                        if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) != pdFALSE )
                                                        {
                                                                /* The task waiting has a higher priority that this task. */
                                                                taskYIELD();
                                                        }
                                                }

                                        }

                                        xReturn = pdPASS;
                                }
                                else
                                {
                                        xReturn = errQUEUE_EMPTY;
                                }
                        }
                        taskEXIT_CRITICAL();

                        if( xReturn == errQUEUE_EMPTY )
                        {
                                if( xTicksToWait > ( portTickType ) 0 )
                                {
                                        if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
                                        {
                                                xReturn = queueERRONEOUS_UNBLOCK;
                                        }
                                        else
                                        {
                                                traceQUEUE_RECEIVE_FAILED( pxQueue );
                                        }
                                }
                                else
                                {
                                        traceQUEUE_RECEIVE_FAILED( pxQueue );
                                }
                        }
                } while( xReturn == queueERRONEOUS_UNBLOCK );

                return xReturn;
        }


#endif /* configUSE_ALTERNATIVE_API */
/*-----------------------------------------------------------*/

signed portBASE_TYPE xQueueGenericSendFromISR( xQueueHandle pxQueue, const void * const pvItemToQueue, signed portBASE_TYPE *pxHigherPriorityTaskWoken, portBASE_TYPE xCopyPosition )
{
signed portBASE_TYPE xReturn;
unsigned portBASE_TYPE uxSavedInterruptStatus;

        /* Similar to xQueueGenericSend, except we don't block if there is no room
        in the queue.  Also we don't directly wake a task that was blocked on a
        queue read, instead we return a flag to say whether a context switch is
        required or not (i.e. has a task with a higher priority than us been woken
        by this post). */
        uxSavedInterruptStatus = portSET_INTERRUPT_MASK_FROM_ISR();
        {
                if( pxQueue->uxMessagesWaiting < pxQueue->uxLength )
                {
                        traceQUEUE_SEND_FROM_ISR( pxQueue );

                        prvCopyDataToQueue( pxQueue, pvItemToQueue, xCopyPosition );

                        /* If the queue is locked we do not alter the event list.  This will
                        be done when the queue is unlocked later. */
                        if( pxQueue->xTxLock == queueUNLOCKED )
                        {
                                if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) )
                                {
                                        if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) != pdFALSE )
                                        {
                                                /* The task waiting has a higher priority so record that a
                                                context switch is required. */
                                                *pxHigherPriorityTaskWoken = pdTRUE;
                                        }
                                }
                        }
                        else
                        {
                                /* Increment the lock count so the task that unlocks the queue
                                knows that data was posted while it was locked. */
                                ++( pxQueue->xTxLock );
                        }

                        xReturn = pdPASS;
                }
                else
                {
                        traceQUEUE_SEND_FROM_ISR_FAILED( pxQueue );
                        xReturn = errQUEUE_FULL;
                }
        }
        portCLEAR_INTERRUPT_MASK_FROM_ISR( uxSavedInterruptStatus );

        return xReturn;
}
/*-----------------------------------------------------------*/

signed portBASE_TYPE xQueueGenericReceive( xQueueHandle pxQueue, void * const pvBuffer, portTickType xTicksToWait, portBASE_TYPE xJustPeeking )
{
signed portBASE_TYPE xReturn = pdTRUE;
xTimeOutType xTimeOut;
signed portCHAR *pcOriginalReadPosition;

        do
        {
                /* If there are no messages in the queue we may have to block. */
                if( xTicksToWait > ( portTickType ) 0 )
                {
                        vTaskSuspendAll();
                        prvLockQueue( pxQueue );

                        if( xReturn == pdTRUE )
                        {
                                /* This is the first time through - we need to capture the
                                time while the scheduler is locked to ensure we attempt to
                                block at least once. */
                                vTaskSetTimeOutState( &xTimeOut );
                        }

                        if( prvIsQueueEmpty( pxQueue ) )
                        {
                        /* Need to call xTaskCheckForTimeout again as time could
                        have passed since it was last called if this is not the
                        first time around this loop. */
                                if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
                                {
                                        traceBLOCKING_ON_QUEUE_RECEIVE( pxQueue );

                                        #if ( configUSE_MUTEXES == 1 )
                                        {
                                                if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
                                                {
                                                        portENTER_CRITICAL();
                                                                vTaskPriorityInherit( ( void * ) pxQueue->pxMutexHolder );
                                                        portEXIT_CRITICAL();
                                                }
                                        }
                                        #endif

                                        vTaskPlaceOnEventList( &( pxQueue->xTasksWaitingToReceive ), xTicksToWait );
                                        prvUnlockQueue( pxQueue );
                                        if( !xTaskResumeAll() )
                                        {
                                                taskYIELD();
                                        }
                                }
                                else
                                {
                                        prvUnlockQueue( pxQueue );
                                        ( void ) xTaskResumeAll();
                                }
                        }
                        else
                        {
                                prvUnlockQueue( pxQueue );
                                ( void ) xTaskResumeAll();
                        }
                }

/* The two tasks are blocked on the queue, the low priority task is polling/running. */

/* An interrupt occurs here - which unblocks the HP tasks, but they do not run. */
                taskENTER_CRITICAL();
                {
/* Because the interrupt occurred the LP task manages to grab the data as the other two tasks are not yet running. */
                        if( pxQueue->uxMessagesWaiting > ( unsigned portBASE_TYPE ) 0 )
                        {
                                /* Remember our read position in case we are just peeking. */
                                pcOriginalReadPosition = pxQueue->pcReadFrom;

                                prvCopyDataFromQueue( pxQueue, pvBuffer );

                                if( xJustPeeking == pdFALSE )
                                {
                                        traceQUEUE_RECEIVE( pxQueue );

                                        /* We are actually removing data. */
                                        --( pxQueue->uxMessagesWaiting );

                                        #if ( configUSE_MUTEXES == 1 )
                                        {
                                                if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
                                                {
                                                        /* Record the information required to implement
                                                        priority inheritance should it become necessary. */
                                                        pxQueue->pxMutexHolder = xTaskGetCurrentTaskHandle();
                                                }
                                        }
                                        #endif

                                        if( listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) == pdFALSE )
                                        {
                                                if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) == pdTRUE )
                                                {
                                                        taskYIELD();
                                                }
                                        }
                                }
                                else
                                {
                                        traceQUEUE_PEEK( pxQueue );

                                        /* We are not removing the data, so reset our read
                                        pointer. */
                                        pxQueue->pcReadFrom = pcOriginalReadPosition;

                                        /* The data is being left in the queue, so see if there are
                                        any other tasks waiting for the data. */
                                        if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) )
                                        {
                                                /* Tasks that are removed from the event list will get added to
                                                the pending ready list as the scheduler is still suspended. */
                                                if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) != pdFALSE )
                                                {
                                                        /* The task waiting has a higher priority than this task. */
                                                        taskYIELD();
                                                }
                                        }

                                }

                                xReturn = pdPASS;
                        }
                        else
                        {
                                xReturn = errQUEUE_EMPTY;
                        }
                }
                taskEXIT_CRITICAL();

                if( xReturn == errQUEUE_EMPTY )
                {
                        if( xTicksToWait > ( portTickType ) 0 )
                        {
                                if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
                                {
                                        xReturn = queueERRONEOUS_UNBLOCK;
                                }
                                else
                                {
                                        traceQUEUE_RECEIVE_FAILED( pxQueue );
                                }
                        }
                        else
                        {
                                traceQUEUE_RECEIVE_FAILED( pxQueue );
                        }
                }

        } while( xReturn == queueERRONEOUS_UNBLOCK );

        return xReturn;
}
/*-----------------------------------------------------------*/

signed portBASE_TYPE xQueueReceiveFromISR( xQueueHandle pxQueue, void * const pvBuffer, signed portBASE_TYPE *pxTaskWoken )
{
signed portBASE_TYPE xReturn;
unsigned portBASE_TYPE uxSavedInterruptStatus;

        uxSavedInterruptStatus = portSET_INTERRUPT_MASK_FROM_ISR();
        {
                /* We cannot block from an ISR, so check there is data available. */
                if( pxQueue->uxMessagesWaiting > ( unsigned portBASE_TYPE ) 0 )
                {
                        traceQUEUE_RECEIVE_FROM_ISR( pxQueue );

                        prvCopyDataFromQueue( pxQueue, pvBuffer );
                        --( pxQueue->uxMessagesWaiting );

                        /* If the queue is locked we will not modify the event list.  Instead
                        we update the lock count so the task that unlocks the queue will know
                        that an ISR has removed data while the queue was locked. */
                        if( pxQueue->xRxLock == queueUNLOCKED )
                        {
                                if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) )
                                {
                                        if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) != pdFALSE )
                                        {
                                                /* The task waiting has a higher priority than us so
                                                force a context switch. */
                                                *pxTaskWoken = pdTRUE;
                                        }
                                }
                        }
                        else
                        {
                                /* Increment the lock count so the task that unlocks the queue
                                knows that data was removed while it was locked. */
                                ++( pxQueue->xRxLock );
                        }

                        xReturn = pdPASS;
                }
                else
                {
                        xReturn = pdFAIL;
                        traceQUEUE_RECEIVE_FROM_ISR_FAILED( pxQueue );
                }
        }
        portCLEAR_INTERRUPT_MASK_FROM_ISR( uxSavedInterruptStatus );

        return xReturn;
}
/*-----------------------------------------------------------*/

unsigned portBASE_TYPE uxQueueMessagesWaiting( const xQueueHandle pxQueue )
{
unsigned portBASE_TYPE uxReturn;

        taskENTER_CRITICAL();
                uxReturn = pxQueue->uxMessagesWaiting;
        taskEXIT_CRITICAL();

        return uxReturn;
}
/*-----------------------------------------------------------*/

unsigned portBASE_TYPE uxQueueMessagesWaitingFromISR( const xQueueHandle pxQueue )
{
unsigned portBASE_TYPE uxReturn;

        uxReturn = pxQueue->uxMessagesWaiting;

        return uxReturn;
}
/*-----------------------------------------------------------*/

void vQueueDelete( xQueueHandle pxQueue )
{
        traceQUEUE_DELETE( pxQueue );
        vQueueUnregisterQueue( pxQueue );
        vPortFree( pxQueue->pcHead );
        vPortFree( pxQueue );
}
/*-----------------------------------------------------------*/

static void prvCopyDataToQueue( xQUEUE *pxQueue, const void *pvItemToQueue, portBASE_TYPE xPosition )
{
        if( pxQueue->uxItemSize == ( unsigned portBASE_TYPE ) 0 )
        {
                #if ( configUSE_MUTEXES == 1 )
                {
                        if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
                        {
                                /* The mutex is no longer being held. */
                                vTaskPriorityDisinherit( ( void * ) pxQueue->pxMutexHolder );
                pxQueue->pxMutexHolder = NULL;
                        }
                }
                #endif
        }
        else if( xPosition == queueSEND_TO_BACK )
        {
                memcpy( ( void * ) pxQueue->pcWriteTo, pvItemToQueue, ( unsigned ) pxQueue->uxItemSize );
                pxQueue->pcWriteTo += pxQueue->uxItemSize;
                if( pxQueue->pcWriteTo >= pxQueue->pcTail )
                {
                        pxQueue->pcWriteTo = pxQueue->pcHead;
                }
        }
        else
        {
                memcpy( ( void * ) pxQueue->pcReadFrom, pvItemToQueue, ( unsigned ) pxQueue->uxItemSize );
                pxQueue->pcReadFrom -= pxQueue->uxItemSize;
                if( pxQueue->pcReadFrom < pxQueue->pcHead )
                {
                        pxQueue->pcReadFrom = ( pxQueue->pcTail - pxQueue->uxItemSize );
                }
        }

        ++( pxQueue->uxMessagesWaiting );
}
/*-----------------------------------------------------------*/

static void prvCopyDataFromQueue( xQUEUE * const pxQueue, const void *pvBuffer )
{
        if( pxQueue->uxQueueType != queueQUEUE_IS_MUTEX )
        {
                pxQueue->pcReadFrom += pxQueue->uxItemSize;
                if( pxQueue->pcReadFrom >= pxQueue->pcTail )
                {
                        pxQueue->pcReadFrom = pxQueue->pcHead;
                }
                memcpy( ( void * ) pvBuffer, ( void * ) pxQueue->pcReadFrom, ( unsigned ) pxQueue->uxItemSize );
        }
}
/*-----------------------------------------------------------*/

static void prvUnlockQueue( xQueueHandle pxQueue )
{
        /* THIS FUNCTION MUST BE CALLED WITH THE SCHEDULER SUSPENDED. */

        /* The lock counts contains the number of extra data items placed or
        removed from the queue while the queue was locked.  When a queue is
        locked items can be added or removed, but the event lists cannot be
        updated. */
        taskENTER_CRITICAL();
        {
                /* See if data was added to the queue while it was locked. */
                while( pxQueue->xTxLock > queueLOCKED_UNMODIFIED )
                {
                        /* Data was posted while the queue was locked.  Are any tasks
                        blocked waiting for data to become available? */
                        if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) )
                        {
                                /* Tasks that are removed from the event list will get added to
                                the pending ready list as the scheduler is still suspended. */
                                if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) != pdFALSE )
                                {
                                        /* The task waiting has a higher priority so record that a
                                        context switch is required. */
                                        vTaskMissedYield();
                                }

                                --( pxQueue->xTxLock );
                        }
                        else
                        {
                                break;
                        }
                }

                pxQueue->xTxLock = queueUNLOCKED;
        }
        taskEXIT_CRITICAL();

        /* Do the same for the Rx lock. */
        taskENTER_CRITICAL();
        {
                while( pxQueue->xRxLock > queueLOCKED_UNMODIFIED )
                {
                        if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) )
                        {
                                if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) != pdFALSE )
                                {
                                        vTaskMissedYield();
                                }

                                --( pxQueue->xRxLock );
                        }
                        else
                        {
                                break;
                        }
                }

                pxQueue->xRxLock = queueUNLOCKED;
        }
        taskEXIT_CRITICAL();
}
/*-----------------------------------------------------------*/

static signed portBASE_TYPE prvIsQueueEmpty( const xQueueHandle pxQueue )
{
signed portBASE_TYPE xReturn;

        taskENTER_CRITICAL();
                xReturn = ( pxQueue->uxMessagesWaiting == ( unsigned portBASE_TYPE ) 0 );
        taskEXIT_CRITICAL();

        return xReturn;
}
/*-----------------------------------------------------------*/

signed portBASE_TYPE xQueueIsQueueEmptyFromISR( const xQueueHandle pxQueue )
{
signed portBASE_TYPE xReturn;

        xReturn = ( pxQueue->uxMessagesWaiting == ( unsigned portBASE_TYPE ) 0 );

        return xReturn;
}
/*-----------------------------------------------------------*/

static signed portBASE_TYPE prvIsQueueFull( const xQueueHandle pxQueue )
{
signed portBASE_TYPE xReturn;

        taskENTER_CRITICAL();
                xReturn = ( pxQueue->uxMessagesWaiting == pxQueue->uxLength );
        taskEXIT_CRITICAL();

        return xReturn;
}
/*-----------------------------------------------------------*/

signed portBASE_TYPE xQueueIsQueueFullFromISR( const xQueueHandle pxQueue )
{
signed portBASE_TYPE xReturn;

        xReturn = ( pxQueue->uxMessagesWaiting == pxQueue->uxLength );

        return xReturn;
}
/*-----------------------------------------------------------*/

#if configUSE_CO_ROUTINES == 1
signed portBASE_TYPE xQueueCRSend( xQueueHandle pxQueue, const void *pvItemToQueue, portTickType xTicksToWait )
{
signed portBASE_TYPE xReturn;

        /* If the queue is already full we may have to block.  A critical section
        is required to prevent an interrupt removing something from the queue
        between the check to see if the queue is full and blocking on the queue. */
        portDISABLE_INTERRUPTS();
        {
                if( prvIsQueueFull( pxQueue ) )
                {
                        /* The queue is full - do we want to block or just leave without
                        posting? */
                        if( xTicksToWait > ( portTickType ) 0 )
                        {
                                /* As this is called from a coroutine we cannot block directly, but
                                return indicating that we need to block. */
                                vCoRoutineAddToDelayedList( xTicksToWait, &( pxQueue->xTasksWaitingToSend ) );
                                portENABLE_INTERRUPTS();
                                return errQUEUE_BLOCKED;
                        }
                        else
                        {
                                portENABLE_INTERRUPTS();
                                return errQUEUE_FULL;
                        }
                }
        }
        portENABLE_INTERRUPTS();

        portNOP();

        portDISABLE_INTERRUPTS();
        {
                if( pxQueue->uxMessagesWaiting < pxQueue->uxLength )
                {
                        /* There is room in the queue, copy the data into the queue. */
                        prvCopyDataToQueue( pxQueue, pvItemToQueue, queueSEND_TO_BACK );
                        xReturn = pdPASS;

                        /* Were any co-routines waiting for data to become available? */
                        if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) )
                        {
                                /* In this instance the co-routine could be placed directly
                                into the ready list as we are within a critical section.
                                Instead the same pending ready list mechanism is used as if
                                the event were caused from within an interrupt. */
                                if( xCoRoutineRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) != pdFALSE )
                                {
                                        /* The co-routine waiting has a higher priority so record
                                        that a yield might be appropriate. */
                                        xReturn = errQUEUE_YIELD;
                                }
                        }
                }
                else
                {
                        xReturn = errQUEUE_FULL;
                }
        }
        portENABLE_INTERRUPTS();

        return xReturn;
}
#endif
/*-----------------------------------------------------------*/

#if configUSE_CO_ROUTINES == 1
signed portBASE_TYPE xQueueCRReceive( xQueueHandle pxQueue, void *pvBuffer, portTickType xTicksToWait )
{
signed portBASE_TYPE xReturn;

        /* If the queue is already empty we may have to block.  A critical section
        is required to prevent an interrupt adding something to the queue
        between the check to see if the queue is empty and blocking on the queue. */
        portDISABLE_INTERRUPTS();
        {
                if( pxQueue->uxMessagesWaiting == ( unsigned portBASE_TYPE ) 0 )
                {
                        /* There are no messages in the queue, do we want to block or just
                        leave with nothing? */
                        if( xTicksToWait > ( portTickType ) 0 )
                        {
                                /* As this is a co-routine we cannot block directly, but return
                                indicating that we need to block. */
                                vCoRoutineAddToDelayedList( xTicksToWait, &( pxQueue->xTasksWaitingToReceive ) );
                                portENABLE_INTERRUPTS();
                                return errQUEUE_BLOCKED;
                        }
                        else
                        {
                                portENABLE_INTERRUPTS();
                                return errQUEUE_FULL;
                        }
                }
        }
        portENABLE_INTERRUPTS();

        portNOP();

        portDISABLE_INTERRUPTS();
        {
                if( pxQueue->uxMessagesWaiting > ( unsigned portBASE_TYPE ) 0 )
                {
                        /* Data is available from the queue. */
                        pxQueue->pcReadFrom += pxQueue->uxItemSize;
                        if( pxQueue->pcReadFrom >= pxQueue->pcTail )
                        {
                                pxQueue->pcReadFrom = pxQueue->pcHead;
                        }
                        --( pxQueue->uxMessagesWaiting );
                        memcpy( ( void * ) pvBuffer, ( void * ) pxQueue->pcReadFrom, ( unsigned ) pxQueue->uxItemSize );

                        xReturn = pdPASS;

                        /* Were any co-routines waiting for space to become available? */
                        if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) )
                        {
                                /* In this instance the co-routine could be placed directly
                                into the ready list as we are within a critical section.
                                Instead the same pending ready list mechanism is used as if
                                the event were caused from within an interrupt. */
                                if( xCoRoutineRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) != pdFALSE )
                                {
                                        xReturn = errQUEUE_YIELD;
                                }
                        }
                }
                else
                {
                        xReturn = pdFAIL;
                }
        }
        portENABLE_INTERRUPTS();

        return xReturn;
}
#endif
/*-----------------------------------------------------------*/



#if configUSE_CO_ROUTINES == 1
signed portBASE_TYPE xQueueCRSendFromISR( xQueueHandle pxQueue, const void *pvItemToQueue, signed portBASE_TYPE xCoRoutinePreviouslyWoken )
{
        /* Cannot block within an ISR so if there is no space on the queue then
        exit without doing anything. */
        if( pxQueue->uxMessagesWaiting < pxQueue->uxLength )
        {
                prvCopyDataToQueue( pxQueue, pvItemToQueue, queueSEND_TO_BACK );

                /* We only want to wake one co-routine per ISR, so check that a
                co-routine has not already been woken. */
                if( !xCoRoutinePreviouslyWoken )
                {
                        if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) )
                        {
                                if( xCoRoutineRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) != pdFALSE )
                                {
                                        return pdTRUE;
                                }
                        }
                }
        }

        return xCoRoutinePreviouslyWoken;
}
#endif
/*-----------------------------------------------------------*/

#if configUSE_CO_ROUTINES == 1
signed portBASE_TYPE xQueueCRReceiveFromISR( xQueueHandle pxQueue, void *pvBuffer, signed portBASE_TYPE *pxCoRoutineWoken )
{
signed portBASE_TYPE xReturn;

        /* We cannot block from an ISR, so check there is data available. If
        not then just leave without doing anything. */
        if( pxQueue->uxMessagesWaiting > ( unsigned portBASE_TYPE ) 0 )
        {
                /* Copy the data from the queue. */
                pxQueue->pcReadFrom += pxQueue->uxItemSize;
                if( pxQueue->pcReadFrom >= pxQueue->pcTail )
                {
                        pxQueue->pcReadFrom = pxQueue->pcHead;
                }
                --( pxQueue->uxMessagesWaiting );
                memcpy( ( void * ) pvBuffer, ( void * ) pxQueue->pcReadFrom, ( unsigned ) pxQueue->uxItemSize );

                if( !( *pxCoRoutineWoken ) )
                {
                        if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) )
                        {
                                if( xCoRoutineRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) != pdFALSE )
                                {
                                        *pxCoRoutineWoken = pdTRUE;
                                }
                        }
                }

                xReturn = pdPASS;
        }
        else
        {
                xReturn = pdFAIL;
        }

        return xReturn;
}
#endif
/*-----------------------------------------------------------*/

#if configQUEUE_REGISTRY_SIZE > 0

        void vQueueAddToRegistry( xQueueHandle xQueue, signed portCHAR *pcQueueName )
        {
        unsigned portBASE_TYPE ux;

                /* See if there is an empty space in the registry.  A NULL name denotes
                a free slot. */
                for( ux = 0; ux < configQUEUE_REGISTRY_SIZE; ux++ )
                {
                        if( xQueueRegistry[ ux ].pcQueueName == NULL )
                        {
                                /* Store the information on this queue. */
                                xQueueRegistry[ ux ].pcQueueName = pcQueueName;
                                xQueueRegistry[ ux ].xHandle = xQueue;
                                break;
                        }
                }
        }

#endif
        /*-----------------------------------------------------------*/

#if configQUEUE_REGISTRY_SIZE > 0

        static void vQueueUnregisterQueue( xQueueHandle xQueue )
        {
        unsigned portBASE_TYPE ux;

                /* See if the handle of the queue being unregistered in actually in the
                registry. */
                for( ux = 0; ux < configQUEUE_REGISTRY_SIZE; ux++ )
                {
                        if( xQueueRegistry[ ux ].xHandle == xQueue )
                        {
                                /* Set the name to NULL to show that this slot if free again. */
                                xQueueRegistry[ ux ].pcQueueName = NULL;
                                break;
                        }
                }
        }

#endif