queue.h

/*
 * FreeRTOS Kernel V10.0.0
 * Copyright (C) 2017 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software. If you wish to use our Amazon
 * FreeRTOS name, please do so in a fair use way that does not cause confusion.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
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 * 1 tab == 4 spaces!
 */
 
#ifndef QUEUE_H
#define QUEUE_H
 
#ifndef INC_FREERTOS_H
#error "include FreeRTOS.h" must appear in source files before "include queue.h"
#endif
 
#ifdef __cplusplus
extern "C" {
#endif
 
/**
 * Type by which queues are referenced.  For example, a call to xQueueCreate()
 * returns an QueueHandle_t variable that can then be used as a parameter to
 * xQueueSend(), xQueueReceive(), etc.
 */
typedef void *QueueHandle_t;
 
/**
 * Type by which queue sets are referenced.  For example, a call to
 * xQueueCreateSet() returns an xQueueSet variable that can then be used as a
 * parameter to xQueueSelectFromSet(), xQueueAddToSet(), etc.
 */
typedef void *QueueSetHandle_t;
 
/**
 * Queue sets can contain both queues and semaphores, so the
 * QueueSetMemberHandle_t is defined as a type to be used where a parameter or
 * return value can be either an QueueHandle_t or an SemaphoreHandle_t.
 */
typedef void *QueueSetMemberHandle_t;
 
/* For internal use only. */
#define queueSEND_TO_BACK ((BaseType_t)0)
#define queueSEND_TO_FRONT ((BaseType_t)1)
#define queueOVERWRITE ((BaseType_t)2)
 
/* For internal use only.  These definitions *must* match those in queue.c. */
#define queueQUEUE_TYPE_BASE ((uint8_t)0U)
#define queueQUEUE_TYPE_SET ((uint8_t)0U)
#define queueQUEUE_TYPE_MUTEX ((uint8_t)1U)
#define queueQUEUE_TYPE_COUNTING_SEMAPHORE ((uint8_t)2U)
#define queueQUEUE_TYPE_BINARY_SEMAPHORE ((uint8_t)3U)
#define queueQUEUE_TYPE_RECURSIVE_MUTEX ((uint8_t)4U)
 
/**
 * queue. h
 * <pre>
 QueueHandle_t xQueueCreate(
                              UBaseType_t uxQueueLength,
                              UBaseType_t uxItemSize
                          );
 * </pre>
 *
 * Creates a new queue instance, and returns a handle by which the new queue
 * can be referenced.
 *
 * Internally, within the FreeRTOS implementation, queues use two blocks of
 * memory.  The first block is used to hold the queue's data structures.  The
 * second block is used to hold items placed into the queue.  If a queue is
 * created using xQueueCreate() then both blocks of memory are automatically
 * dynamically allocated inside the xQueueCreate() function.  (see
 * http://www.freertos.org/a00111.html).  If a queue is created using
 * xQueueCreateStatic() then the application writer must provide the memory that
 * will get used by the queue.  xQueueCreateStatic() therefore allows a queue to
 * be created without using any dynamic memory allocation.
 *
 * http://www.FreeRTOS.org/Embedded-RTOS-Queues.html
 *
 * @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
 {
    char ucMessageID;
    char ucData[ 20 ];
 };
 
 void vATask( void *pvParameters )
 {
 QueueHandle_t xQueue1, xQueue2;
 
    // Create a queue capable of containing 10 uint32_t values.
    xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
    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
 */
#if (configSUPPORT_DYNAMIC_ALLOCATION == 1)
#define xQueueCreate(uxQueueLength, uxItemSize)                                                                        \
    xQueueGenericCreate((uxQueueLength), (uxItemSize), (queueQUEUE_TYPE_BASE))
#endif
 
/**
 * queue. h
 * <pre>
 QueueHandle_t xQueueCreateStatic(
                              UBaseType_t uxQueueLength,
                              UBaseType_t uxItemSize,
                              uint8_t *pucQueueStorageBuffer,
                              StaticQueue_t *pxQueueBuffer
                          );
 * </pre>
 *
 * Creates a new queue instance, and returns a handle by which the new queue
 * can be referenced.
 *
 * Internally, within the FreeRTOS implementation, queues use two blocks of
 * memory.  The first block is used to hold the queue's data structures.  The
 * second block is used to hold items placed into the queue.  If a queue is
 * created using xQueueCreate() then both blocks of memory are automatically
 * dynamically allocated inside the xQueueCreate() function.  (see
 * http://www.freertos.org/a00111.html).  If a queue is created using
 * xQueueCreateStatic() then the application writer must provide the memory that
 * will get used by the queue.  xQueueCreateStatic() therefore allows a queue to
 * be created without using any dynamic memory allocation.
 *
 * http://www.FreeRTOS.org/Embedded-RTOS-Queues.html
 *
 * @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.
 *
 * @param pucQueueStorageBuffer If uxItemSize is not zero then
 * pucQueueStorageBuffer must point to a uint8_t array that is at least large
 * enough to hold the maximum number of items that can be in the queue at any
 * one time - which is ( uxQueueLength * uxItemsSize ) bytes.  If uxItemSize is
 * zero then pucQueueStorageBuffer can be NULL.
 *
 * @param pxQueueBuffer Must point to a variable of type StaticQueue_t, which
 * will be used to hold the queue's data structure.
 *
 * @return If the queue is created then a handle to the created queue is
 * returned.  If pxQueueBuffer is NULL then NULL is returned.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    char ucMessageID;
    char ucData[ 20 ];
 };
 
 #define QUEUE_LENGTH 10
 #define ITEM_SIZE sizeof( uint32_t )
 
 // xQueueBuffer will hold the queue structure.
 StaticQueue_t xQueueBuffer;
 
 // ucQueueStorage will hold the items posted to the queue.  Must be at least
 // [(queue length) * ( queue item size)] bytes long.
 uint8_t ucQueueStorage[ QUEUE_LENGTH * ITEM_SIZE ];
 
 void vATask( void *pvParameters )
 {
 QueueHandle_t xQueue1;
 
    // Create a queue capable of containing 10 uint32_t values.
    xQueue1 = xQueueCreate( QUEUE_LENGTH, // The number of items the queue can hold.
                            ITEM_SIZE     // The size of each item in the queue
                            &( ucQueueStorage[ 0 ] ), // The buffer that will hold the items in the queue.
                            &xQueueBuffer ); // The buffer that will hold the queue structure.
 
    // The queue is guaranteed to be created successfully as no dynamic memory
    // allocation is used.  Therefore xQueue1 is now a handle to a valid queue.
 
    // ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueCreateStatic xQueueCreateStatic
 * \ingroup QueueManagement
 */
#if (configSUPPORT_STATIC_ALLOCATION == 1)
#define xQueueCreateStatic(uxQueueLength, uxItemSize, pucQueueStorage, pxQueueBuffer)                                  \
    xQueueGenericCreateStatic((uxQueueLength), (uxItemSize), (pucQueueStorage), (pxQueueBuffer), (queueQUEUE_TYPE_BASE))
#endif /* configSUPPORT_STATIC_ALLOCATION */
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueSendToToFront(
                                   QueueHandle_t    xQueue,
                                   const void       *pvItemToQueue,
                                   TickType_t       xTicksToWait
                               );
 * </pre>
 *
 * Post an item to the front of 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 and the
 * queue is full.  The time is defined in tick periods so the constant
 * portTICK_PERIOD_MS should be used to convert to real time if this is required.
 *
 * @return pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    char ucMessageID;
    char ucData[ 20 ];
 } xMessage;
 
 uint32_t ulVar = 10UL;
 
 void vATask( void *pvParameters )
 {
 QueueHandle_t xQueue1, xQueue2;
 struct AMessage *pxMessage;
 
    // Create a queue capable of containing 10 uint32_t values.
    xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
 
    // 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 uint32_t.  Wait for 10 ticks for space to become
        // available if necessary.
        if( xQueueSendToFront( xQueue1, ( void * ) &ulVar, ( TickType_t ) 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;
        xQueueSendToFront( xQueue2, ( void * ) &pxMessage, ( TickType_t ) 0 );
    }
 
    // ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueSend xQueueSend
 * \ingroup QueueManagement
 */
#define xQueueSendToFront(xQueue, pvItemToQueue, xTicksToWait)                                                         \
    xQueueGenericSend((xQueue), (pvItemToQueue), (xTicksToWait), queueSEND_TO_FRONT)
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueSendToBack(
                                   QueueHandle_t    xQueue,
                                   const void       *pvItemToQueue,
                                   TickType_t       xTicksToWait
                               );
 * </pre>
 *
 * This is a macro that calls xQueueGenericSend().
 *
 * Post an item to the back of 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 and the queue
 * is full.  The  time is defined in tick periods so the constant
 * portTICK_PERIOD_MS should be used to convert to real time if this is required.
 *
 * @return pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    char ucMessageID;
    char ucData[ 20 ];
 } xMessage;
 
 uint32_t ulVar = 10UL;
 
 void vATask( void *pvParameters )
 {
 QueueHandle_t xQueue1, xQueue2;
 struct AMessage *pxMessage;
 
    // Create a queue capable of containing 10 uint32_t values.
    xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
 
    // 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 uint32_t.  Wait for 10 ticks for space to become
        // available if necessary.
        if( xQueueSendToBack( xQueue1, ( void * ) &ulVar, ( TickType_t ) 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;
        xQueueSendToBack( xQueue2, ( void * ) &pxMessage, ( TickType_t ) 0 );
    }
 
    // ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueSend xQueueSend
 * \ingroup QueueManagement
 */
#define xQueueSendToBack(xQueue, pvItemToQueue, xTicksToWait)                                                          \
    xQueueGenericSend((xQueue), (pvItemToQueue), (xTicksToWait), queueSEND_TO_BACK)
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueSend(
                              QueueHandle_t xQueue,
                              const void * pvItemToQueue,
                              TickType_t xTicksToWait
                         );
 * </pre>
 *
 * This is a macro that calls xQueueGenericSend().  It is included for
 * backward compatibility with versions of FreeRTOS.org that did not
 * include the xQueueSendToFront() and xQueueSendToBack() macros.  It is
 * equivalent to xQueueSendToBack().
 *
 * 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 and the
 * queue is full.  The time is defined in tick periods so the constant
 * portTICK_PERIOD_MS should be used to convert to real time if this is required.
 *
 * @return pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    char ucMessageID;
    char ucData[ 20 ];
 } xMessage;
 
 uint32_t ulVar = 10UL;
 
 void vATask( void *pvParameters )
 {
 QueueHandle_t xQueue1, xQueue2;
 struct AMessage *pxMessage;
 
    // Create a queue capable of containing 10 uint32_t values.
    xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
 
    // 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 uint32_t.  Wait for 10 ticks for space to become
        // available if necessary.
        if( xQueueSend( xQueue1, ( void * ) &ulVar, ( TickType_t ) 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, ( TickType_t ) 0 );
    }
 
    // ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueSend xQueueSend
 * \ingroup QueueManagement
 */
#define xQueueSend(xQueue, pvItemToQueue, xTicksToWait)                                                                \
    xQueueGenericSend((xQueue), (pvItemToQueue), (xTicksToWait), queueSEND_TO_BACK)
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueOverwrite(
                              QueueHandle_t xQueue,
                              const void * pvItemToQueue
                         );
 * </pre>
 *
 * Only for use with queues that have a length of one - so the queue is either
 * empty or full.
 *
 * Post an item on a queue.  If the queue is already full then overwrite the
 * value held in the queue.  The item is queued by copy, not by reference.
 *
 * This function must not be called from an interrupt service routine.
 * See xQueueOverwriteFromISR () for an alternative which may be used in an ISR.
 *
 * @param xQueue The handle of the queue to which the data is being sent.
 *
 * @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.
 *
 * @return xQueueOverwrite() is a macro that calls xQueueGenericSend(), and
 * therefore has the same return values as xQueueSendToFront().  However, pdPASS
 * is the only value that can be returned because xQueueOverwrite() will write
 * to the queue even when the queue is already full.
 *
 * Example usage:
   <pre>
 
 void vFunction( void *pvParameters )
 {
 QueueHandle_t xQueue;
 uint32_t ulVarToSend, ulValReceived;
 
    // Create a queue to hold one uint32_t value.  It is strongly
    // recommended *not* to use xQueueOverwrite() on queues that can
    // contain more than one value, and doing so will trigger an assertion
    // if configASSERT() is defined.
    xQueue = xQueueCreate( 1, sizeof( uint32_t ) );
 
    // Write the value 10 to the queue using xQueueOverwrite().
    ulVarToSend = 10;
    xQueueOverwrite( xQueue, &ulVarToSend );
 
    // Peeking the queue should now return 10, but leave the value 10 in
    // the queue.  A block time of zero is used as it is known that the
    // queue holds a value.
    ulValReceived = 0;
    xQueuePeek( xQueue, &ulValReceived, 0 );
 
    if( ulValReceived != 10 )
    {
        // Error unless the item was removed by a different task.
    }
 
    // The queue is still full.  Use xQueueOverwrite() to overwrite the
    // value held in the queue with 100.
    ulVarToSend = 100;
    xQueueOverwrite( xQueue, &ulVarToSend );
 
    // This time read from the queue, leaving the queue empty once more.
    // A block time of 0 is used again.
    xQueueReceive( xQueue, &ulValReceived, 0 );
 
    // The value read should be the last value written, even though the
    // queue was already full when the value was written.
    if( ulValReceived != 100 )
    {
        // Error!
    }
 
    // ...
}
 </pre>
 * \defgroup xQueueOverwrite xQueueOverwrite
 * \ingroup QueueManagement
 */
#define xQueueOverwrite(xQueue, pvItemToQueue) xQueueGenericSend((xQueue), (pvItemToQueue), 0, queueOVERWRITE)
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueGenericSend(
                                    QueueHandle_t xQueue,
                                    const void * pvItemToQueue,
                                    TickType_t xTicksToWait
                                    BaseType_t xCopyPosition
                                );
 * </pre>
 *
 * It is preferred that the macros xQueueSend(), xQueueSendToFront() and
 * xQueueSendToBack() are used in place of calling this function directly.
 *
 * 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 and the
 * queue is full.  The time is defined in tick periods so the constant
 * portTICK_PERIOD_MS should be used to convert to real time if this is required.
 *
 * @param xCopyPosition Can take the value queueSEND_TO_BACK to place the
 * item at the back of the queue, or queueSEND_TO_FRONT to place the item
 * at the front of the queue (for high priority messages).
 *
 * @return pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    char ucMessageID;
    char ucData[ 20 ];
 } xMessage;
 
 uint32_t ulVar = 10UL;
 
 void vATask( void *pvParameters )
 {
 QueueHandle_t xQueue1, xQueue2;
 struct AMessage *pxMessage;
 
    // Create a queue capable of containing 10 uint32_t values.
    xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
 
    // 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 uint32_t.  Wait for 10 ticks for space to become
        // available if necessary.
        if( xQueueGenericSend( xQueue1, ( void * ) &ulVar, ( TickType_t ) 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, ( TickType_t ) 0, queueSEND_TO_BACK );
    }
 
    // ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueSend xQueueSend
 * \ingroup QueueManagement
 */
BaseType_t xQueueGenericSend(QueueHandle_t xQueue, const void *const pvItemToQueue, TickType_t xTicksToWait,
                             const BaseType_t xCopyPosition) PRIVILEGED_FUNCTION;
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueuePeek(
                             QueueHandle_t xQueue,
                             void * const pvBuffer,
                             TickType_t xTicksToWait
                         );</pre>
 *
 * 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.  See
 * xQueuePeekFromISR() for an alternative that can be called from an interrupt
 * service routine.
 *
 * @param xQueue 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_PERIOD_MS should be used to convert to real time if this is required.
 * xQueuePeek() will return immediately if xTicksToWait is 0 and the queue
 * is empty.
 *
 * @return pdTRUE if an item was successfully received from the queue,
 * otherwise pdFALSE.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    char ucMessageID;
    char ucData[ 20 ];
 } xMessage;
 
 QueueHandle_t xQueue;
 
 // Task to create a queue and post a value.
 void vATask( void *pvParameters )
 {
 struct AMessage *pxMessage;
 
    // Create a queue capable of containing 10 pointers to AMessage structures.
    // These should be passed by pointer as they contain a lot of data.
    xQueue = xQueueCreate( 10, sizeof( struct AMessage * ) );
    if( xQueue == 0 )
    {
        // Failed to create the queue.
    }
 
    // ...
 
    // Send a pointer to a struct AMessage object.  Don't block if the
    // queue is already full.
    pxMessage = & xMessage;
    xQueueSend( xQueue, ( void * ) &pxMessage, ( TickType_t ) 0 );
 
    // ... Rest of task code.
 }
 
 // Task to 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 ), ( TickType_t ) 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 xQueuePeek xQueuePeek
 * \ingroup QueueManagement
 */
BaseType_t xQueuePeek(QueueHandle_t xQueue, void *const pvBuffer, TickType_t xTicksToWait) PRIVILEGED_FUNCTION;
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueuePeekFromISR(
                                    QueueHandle_t xQueue,
                                    void *pvBuffer,
                                );</pre>
 *
 * A version of xQueuePeek() that can be called from an interrupt service
 * routine (ISR).
 *
 * 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().
 *
 * @param xQueue 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.
 *
 * @return pdTRUE if an item was successfully received from the queue,
 * otherwise pdFALSE.
 *
 * \defgroup xQueuePeekFromISR xQueuePeekFromISR
 * \ingroup QueueManagement
 */
BaseType_t xQueuePeekFromISR(QueueHandle_t xQueue, void *const pvBuffer) PRIVILEGED_FUNCTION;
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueReceive(
                                 QueueHandle_t xQueue,
                                 void *pvBuffer,
                                 TickType_t 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.
 *
 * 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 xQueue 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.  xQueueReceive() will return immediately if xTicksToWait
 * is zero and the queue is empty.  The time is defined in tick periods so the
 * constant portTICK_PERIOD_MS should be used to convert to real time if this is
 * required.
 *
 * @return pdTRUE if an item was successfully received from the queue,
 * otherwise pdFALSE.
 *
 * Example usage:
   <pre>
 struct AMessage
 {
    char ucMessageID;
    char ucData[ 20 ];
 } xMessage;
 
 QueueHandle_t xQueue;
 
 // Task to create a queue and post a value.
 void vATask( void *pvParameters )
 {
 struct AMessage *pxMessage;
 
    // Create a queue capable of containing 10 pointers to AMessage structures.
    // These should be passed by pointer as they contain a lot of data.
    xQueue = xQueueCreate( 10, sizeof( struct AMessage * ) );
    if( xQueue == 0 )
    {
        // Failed to create the queue.
    }
 
    // ...
 
    // Send a pointer to a struct AMessage object.  Don't block if the
    // queue is already full.
    pxMessage = & xMessage;
    xQueueSend( xQueue, ( void * ) &pxMessage, ( TickType_t ) 0 );
 
    // ... Rest of task code.
 }
 
 // Task to receive from the queue.
 void vADifferentTask( void *pvParameters )
 {
 struct AMessage *pxRxedMessage;
 
    if( xQueue != 0 )
    {
        // Receive a message on the created queue.  Block for 10 ticks if a
        // message is not immediately available.
        if( xQueueReceive( xQueue, &( pxRxedMessage ), ( TickType_t ) 10 ) )
        {
            // pcRxedMessage now points to the struct AMessage variable posted
            // by vATask.
        }
    }
 
    // ... Rest of task code.
 }
 </pre>
 * \defgroup xQueueReceive xQueueReceive
 * \ingroup QueueManagement
 */
BaseType_t xQueueReceive(QueueHandle_t xQueue, void *const pvBuffer, TickType_t xTicksToWait) PRIVILEGED_FUNCTION;
 
/**
 * queue. h
 * <pre>UBaseType_t uxQueueMessagesWaiting( const QueueHandle_t 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.
 *
 * \defgroup uxQueueMessagesWaiting uxQueueMessagesWaiting
 * \ingroup QueueManagement
 */
UBaseType_t uxQueueMessagesWaiting(const QueueHandle_t xQueue) PRIVILEGED_FUNCTION;
 
/**
 * queue. h
 * <pre>UBaseType_t uxQueueSpacesAvailable( const QueueHandle_t xQueue );</pre>
 *
 * Return the number of free spaces available in a queue.  This is equal to the
 * number of items that can be sent to the queue before the queue becomes full
 * if no items are removed.
 *
 * @param xQueue A handle to the queue being queried.
 *
 * @return The number of spaces available in the queue.
 *
 * \defgroup uxQueueMessagesWaiting uxQueueMessagesWaiting
 * \ingroup QueueManagement
 */
UBaseType_t uxQueueSpacesAvailable(const QueueHandle_t xQueue) PRIVILEGED_FUNCTION;
 
/**
 * queue. h
 * <pre>void vQueueDelete( QueueHandle_t 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.
 *
 * \defgroup vQueueDelete vQueueDelete
 * \ingroup QueueManagement
 */
void vQueueDelete(QueueHandle_t xQueue) PRIVILEGED_FUNCTION;
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueSendToFrontFromISR(
                                         QueueHandle_t xQueue,
                                         const void *pvItemToQueue,
                                         BaseType_t *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 )
 {
 char cIn;
 BaseType_t 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 )
    {
        taskYIELD ();
    }
 }
 </pre>
 *
 * \defgroup xQueueSendFromISR xQueueSendFromISR
 * \ingroup QueueManagement
 */
#define xQueueSendToFrontFromISR(xQueue, pvItemToQueue, pxHigherPriorityTaskWoken)                                     \
    xQueueGenericSendFromISR((xQueue), (pvItemToQueue), (pxHigherPriorityTaskWoken), queueSEND_TO_FRONT)
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueSendToBackFromISR(
                                         QueueHandle_t xQueue,
                                         const void *pvItemToQueue,
                                         BaseType_t *pxHigherPriorityTaskWoken
                                      );
 </pre>
 *
 * This is a macro that calls xQueueGenericSendFromISR().
 *
 * Post an item to the back 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 xQueueSendToBackFromISR() 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 xQueueSendToBackFromISR() 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 )
 {
 char cIn;
 BaseType_t xHigherPriorityTaskWoken;
 
    // 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.
        xQueueSendToBackFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken );
 
    } while( portINPUT_BYTE( BUFFER_COUNT ) );
 
    // Now the buffer is empty we can switch context if necessary.
    if( xHigherPriorityTaskWoken )
    {
        taskYIELD ();
    }
 }
 </pre>
 *
 * \defgroup xQueueSendFromISR xQueueSendFromISR
 * \ingroup QueueManagement
 */
#define xQueueSendToBackFromISR(xQueue, pvItemToQueue, pxHigherPriorityTaskWoken)                                      \
    xQueueGenericSendFromISR((xQueue), (pvItemToQueue), (pxHigherPriorityTaskWoken), queueSEND_TO_BACK)
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueOverwriteFromISR(
                              QueueHandle_t xQueue,
                              const void * pvItemToQueue,
                              BaseType_t *pxHigherPriorityTaskWoken
                         );
 * </pre>
 *
 * A version of xQueueOverwrite() that can be used in an interrupt service
 * routine (ISR).
 *
 * Only for use with queues that can hold a single item - so the queue is either
 * empty or full.
 *
 * Post an item on a queue.  If the queue is already full then overwrite the
 * value held in the queue.  The item is queued by copy, not by reference.
 *
 * @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 xQueueOverwriteFromISR() 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 xQueueOverwriteFromISR() sets this value to pdTRUE then
 * a context switch should be requested before the interrupt is exited.
 *
 * @return xQueueOverwriteFromISR() is a macro that calls
 * xQueueGenericSendFromISR(), and therefore has the same return values as
 * xQueueSendToFrontFromISR().  However, pdPASS is the only value that can be
 * returned because xQueueOverwriteFromISR() will write to the queue even when
 * the queue is already full.
 *
 * Example usage:
   <pre>
 
 QueueHandle_t xQueue;
 
 void vFunction( void *pvParameters )
 {
    // Create a queue to hold one uint32_t value.  It is strongly
    // recommended *not* to use xQueueOverwriteFromISR() on queues that can
    // contain more than one value, and doing so will trigger an assertion
    // if configASSERT() is defined.
    xQueue = xQueueCreate( 1, sizeof( uint32_t ) );
}
 
void vAnInterruptHandler( void )
{
// xHigherPriorityTaskWoken must be set to pdFALSE before it is used.
BaseType_t xHigherPriorityTaskWoken = pdFALSE;
uint32_t ulVarToSend, ulValReceived;
 
    // Write the value 10 to the queue using xQueueOverwriteFromISR().
    ulVarToSend = 10;
    xQueueOverwriteFromISR( xQueue, &ulVarToSend, &xHigherPriorityTaskWoken );
 
    // The queue is full, but calling xQueueOverwriteFromISR() again will still
    // pass because the value held in the queue will be overwritten with the
    // new value.
    ulVarToSend = 100;
    xQueueOverwriteFromISR( xQueue, &ulVarToSend, &xHigherPriorityTaskWoken );
 
    // Reading from the queue will now return 100.
 
    // ...
 
    if( xHigherPrioritytaskWoken == pdTRUE )
    {
        // Writing to the queue caused a task to unblock and the unblocked task
        // has a priority higher than or equal to the priority of the currently
        // executing task (the task this interrupt interrupted).  Perform a context
        // switch so this interrupt returns directly to the unblocked task.
        portYIELD_FROM_ISR(); // or portEND_SWITCHING_ISR() depending on the port.
    }
}
 </pre>
 * \defgroup xQueueOverwriteFromISR xQueueOverwriteFromISR
 * \ingroup QueueManagement
 */
#define xQueueOverwriteFromISR(xQueue, pvItemToQueue, pxHigherPriorityTaskWoken)                                       \
    xQueueGenericSendFromISR((xQueue), (pvItemToQueue), (pxHigherPriorityTaskWoken), queueOVERWRITE)
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueSendFromISR(
                                     QueueHandle_t xQueue,
                                     const void *pvItemToQueue,
                                     BaseType_t *pxHigherPriorityTaskWoken
                                );
 </pre>
 *
 * This is a macro that calls xQueueGenericSendFromISR().  It is included
 * for backward compatibility with versions of FreeRTOS.org that did not
 * include the xQueueSendToBackFromISR() and xQueueSendToFrontFromISR()
 * macros.
 *
 * Post an item to the back of 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 pxHigherPriorityTaskWoken xQueueSendFromISR() 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 xQueueSendFromISR() 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 )
 {
 char cIn;
 BaseType_t xHigherPriorityTaskWoken;
 
    // 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.
        xQueueSendFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken );
 
    } while( portINPUT_BYTE( BUFFER_COUNT ) );
 
    // Now the buffer is empty we can switch context if necessary.
    if( xHigherPriorityTaskWoken )
    {
        // Actual macro used here is port specific.
        portYIELD_FROM_ISR ();
    }
 }
 </pre>
 *
 * \defgroup xQueueSendFromISR xQueueSendFromISR
 * \ingroup QueueManagement
 */
#define xQueueSendFromISR(xQueue, pvItemToQueue, pxHigherPriorityTaskWoken)                                            \
    xQueueGenericSendFromISR((xQueue), (pvItemToQueue), (pxHigherPriorityTaskWoken), queueSEND_TO_BACK)
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueGenericSendFromISR(
                                           QueueHandle_t        xQueue,
                                           const    void    *pvItemToQueue,
                                           BaseType_t   *pxHigherPriorityTaskWoken,
                                           BaseType_t   xCopyPosition
                                       );
 </pre>
 *
 * It is preferred that the macros xQueueSendFromISR(),
 * xQueueSendToFrontFromISR() and xQueueSendToBackFromISR() be used in place
 * of calling this function directly.  xQueueGiveFromISR() is an
 * equivalent for use by semaphores that don't actually copy any data.
 *
 * 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 pxHigherPriorityTaskWoken xQueueGenericSendFromISR() 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 xQueueGenericSendFromISR() sets this value to pdTRUE then
 * a context switch should be requested before the interrupt is exited.
 *
 * @param xCopyPosition Can take the value queueSEND_TO_BACK to place the
 * item at the back of the queue, or queueSEND_TO_FRONT to place the item
 * at the front of the queue (for high priority messages).
 *
 * @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 )
 {
 char cIn;
 BaseType_t xHigherPriorityTaskWokenByPost;
 
    // We have not woken a task at the start of the ISR.
    xHigherPriorityTaskWokenByPost = pdFALSE;
 
    // Loop until the buffer is empty.
    do
    {
        // Obtain a byte from the buffer.
        cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS );
 
        // Post each byte.
        xQueueGenericSendFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWokenByPost, queueSEND_TO_BACK );
 
    } while( portINPUT_BYTE( BUFFER_COUNT ) );
 
    // Now the buffer is empty we can switch context if necessary.  Note that the
    // name of the yield function required is port specific.
    if( xHigherPriorityTaskWokenByPost )
    {
        taskYIELD_YIELD_FROM_ISR();
    }
 }
 </pre>
 *
 * \defgroup xQueueSendFromISR xQueueSendFromISR
 * \ingroup QueueManagement
 */
BaseType_t xQueueGenericSendFromISR(QueueHandle_t xQueue, const void *const pvItemToQueue,
                                    BaseType_t *const pxHigherPriorityTaskWoken,
                                    const BaseType_t  xCopyPosition) PRIVILEGED_FUNCTION;
BaseType_t xQueueGiveFromISR(QueueHandle_t xQueue, BaseType_t *const pxHigherPriorityTaskWoken) PRIVILEGED_FUNCTION;
 
/**
 * queue. h
 * <pre>
 BaseType_t xQueueReceiveFromISR(
                                       QueueHandle_t    xQueue,
                                       void *pvBuffer,
                                       BaseType_t *pxTaskWoken
                                   );
 * </pre>
 *
 * Receive an item from a queue.  It is safe to use this function from within an
 * interrupt service routine.
 *
 * @param xQueue 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>
 
 QueueHandle_t xQueue;
 
 // Function to create a queue and post some values.
 void vAFunction( void *pvParameters )
 {
 char cValueToPost;
 const TickType_t xTicksToWait = ( TickType_t )0xff;
 
    // Create a queue capable of containing 10 characters.
    xQueue = xQueueCreate( 10, sizeof( char ) );
    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 xTicksToWait ticks.
    cValueToPost = 'a';
    xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );
    cValueToPost = 'b';
    xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );
 
    // ... keep posting characters ... this task may block when the queue
    // becomes full.
 
    cValueToPost = 'c';
    xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );
 }
 
 // ISR that outputs all the characters received on the queue.
 void vISR_Routine( void )
 {
 BaseType_t xTaskWokenByReceive = pdFALSE;
 char 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 != ( char ) pdFALSE;
    {
        taskYIELD ();
    }
 }
 </pre>
 * \defgroup xQueueReceiveFromISR xQueueReceiveFromISR
 * \ingroup QueueManagement
 */
BaseType_t xQueueReceiveFromISR(QueueHandle_t xQueue, void *const pvBuffer,
                                BaseType_t *const pxHigherPriorityTaskWoken) PRIVILEGED_FUNCTION;
 
/*
 * Utilities to query queues that are safe to use from an ISR.  These utilities
 * should be used only from witin an ISR, or within a critical section.
 */
BaseType_t  xQueueIsQueueEmptyFromISR(const QueueHandle_t xQueue) PRIVILEGED_FUNCTION;
BaseType_t  xQueueIsQueueFullFromISR(const QueueHandle_t xQueue) PRIVILEGED_FUNCTION;
UBaseType_t uxQueueMessagesWaitingFromISR(const QueueHandle_t xQueue) PRIVILEGED_FUNCTION;
 
/*
 * 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-routines.
 *
 * 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.
 */
BaseType_t xQueueCRSendFromISR(QueueHandle_t xQueue, const void *pvItemToQueue, BaseType_t xCoRoutinePreviouslyWoken);
BaseType_t xQueueCRReceiveFromISR(QueueHandle_t xQueue, void *pvBuffer, BaseType_t *pxTaskWoken);
BaseType_t xQueueCRSend(QueueHandle_t xQueue, const void *pvItemToQueue, TickType_t xTicksToWait);
BaseType_t xQueueCRReceive(QueueHandle_t xQueue, void *pvBuffer, TickType_t xTicksToWait);
 
/*
 * For internal use only.  Use xSemaphoreCreateMutex(),
 * xSemaphoreCreateCounting() or xSemaphoreGetMutexHolder() instead of calling
 * these functions directly.
 */
QueueHandle_t xQueueCreateMutex(const uint8_t ucQueueType) PRIVILEGED_FUNCTION;
QueueHandle_t xQueueCreateMutexStatic(const uint8_t ucQueueType, StaticQueue_t *pxStaticQueue) PRIVILEGED_FUNCTION;
QueueHandle_t xQueueCreateCountingSemaphore(const UBaseType_t uxMaxCount,
                                            const UBaseType_t uxInitialCount) PRIVILEGED_FUNCTION;
QueueHandle_t xQueueCreateCountingSemaphoreStatic(const UBaseType_t uxMaxCount, const UBaseType_t uxInitialCount,
                                                  StaticQueue_t *pxStaticQueue) PRIVILEGED_FUNCTION;
BaseType_t    xQueueSemaphoreTake(QueueHandle_t xQueue, TickType_t xTicksToWait) PRIVILEGED_FUNCTION;
void *        xQueueGetMutexHolder(QueueHandle_t xSemaphore) PRIVILEGED_FUNCTION;
void *        xQueueGetMutexHolderFromISR(QueueHandle_t xSemaphore) PRIVILEGED_FUNCTION;
 
/*
 * For internal use only.  Use xSemaphoreTakeMutexRecursive() or
 * xSemaphoreGiveMutexRecursive() instead of calling these functions directly.
 */
BaseType_t xQueueTakeMutexRecursive(QueueHandle_t xMutex, TickType_t xTicksToWait) PRIVILEGED_FUNCTION;
BaseType_t xQueueGiveMutexRecursive(QueueHandle_t pxMutex) PRIVILEGED_FUNCTION;
 
/*
 * Reset a queue back to its original empty state.  The return value is now
 * obsolete and is always set to pdPASS.
 */
#define xQueueReset(xQueue) xQueueGenericReset(xQueue, pdFALSE)
 
/*
 * The registry is provided as a means for kernel aware debuggers to
 * locate queues, semaphores and mutexes.  Call vQueueAddToRegistry() add
 * a queue, semaphore or mutex handle to the registry if you want the handle
 * to be available to a kernel aware debugger.  If you are not using a kernel
 * aware debugger then this function can be ignored.
 *
 * configQUEUE_REGISTRY_SIZE defines the maximum number of handles the
 * registry can hold.  configQUEUE_REGISTRY_SIZE must be greater than 0
 * within FreeRTOSConfig.h for the registry to be available.  Its value
 * does not effect the number of queues, semaphores and mutexes that can be
 * created - just the number that the registry can hold.
 *
 * @param xQueue The handle of the queue being added to the registry.  This
 * is the handle returned by a call to xQueueCreate().  Semaphore and mutex
 * handles can also be passed in here.
 *
 * @param pcName The name to be associated with the handle.  This is the
 * name that the kernel aware debugger will display.  The queue registry only
 * stores a pointer to the string - so the string must be persistent (global or
 * preferably in ROM/Flash), not on the stack.
 */
#if (configQUEUE_REGISTRY_SIZE > 0)
void vQueueAddToRegistry(QueueHandle_t xQueue, const char *pcName)
    PRIVILEGED_FUNCTION; /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
#endif
 
/*
 * The registry is provided as a means for kernel aware debuggers to
 * locate queues, semaphores and mutexes.  Call vQueueAddToRegistry() add
 * a queue, semaphore or mutex handle to the registry if you want the handle
 * to be available to a kernel aware debugger, and vQueueUnregisterQueue() to
 * remove the queue, semaphore or mutex from the register.  If you are not using
 * a kernel aware debugger then this function can be ignored.
 *
 * @param xQueue The handle of the queue being removed from the registry.
 */
#if (configQUEUE_REGISTRY_SIZE > 0)
void vQueueUnregisterQueue(QueueHandle_t xQueue) PRIVILEGED_FUNCTION;
#endif
 
/*
 * The queue registry is provided as a means for kernel aware debuggers to
 * locate queues, semaphores and mutexes.  Call pcQueueGetName() to look
 * up and return the name of a queue in the queue registry from the queue's
 * handle.
 *
 * @param xQueue The handle of the queue the name of which will be returned.
 * @return If the queue is in the registry then a pointer to the name of the
 * queue is returned.  If the queue is not in the registry then NULL is
 * returned.
 */
#if (configQUEUE_REGISTRY_SIZE > 0)
const char *pcQueueGetName(QueueHandle_t xQueue)
    PRIVILEGED_FUNCTION; /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
#endif
 
/*
 * Generic version of the function used to creaet a queue using dynamic memory
 * allocation.  This is called by other functions and macros that create other
 * RTOS objects that use the queue structure as their base.
 */
#if (configSUPPORT_DYNAMIC_ALLOCATION == 1)
QueueHandle_t xQueueGenericCreate(const UBaseType_t uxQueueLength, const UBaseType_t uxItemSize,
                                  const uint8_t ucQueueType) PRIVILEGED_FUNCTION;
#endif
 
/*
 * Generic version of the function used to creaet a queue using dynamic memory
 * allocation.  This is called by other functions and macros that create other
 * RTOS objects that use the queue structure as their base.
 */
#if (configSUPPORT_STATIC_ALLOCATION == 1)
QueueHandle_t xQueueGenericCreateStatic(const UBaseType_t uxQueueLength, const UBaseType_t uxItemSize,
                                        uint8_t *pucQueueStorage, StaticQueue_t *pxStaticQueue,
                                        const uint8_t ucQueueType) PRIVILEGED_FUNCTION;
#endif
 
/*
 * Queue sets provide a mechanism to allow a task to block (pend) on a read
 * operation from multiple queues or semaphores simultaneously.
 *
 * See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this
 * function.
 *
 * A queue set must be explicitly created using a call to xQueueCreateSet()
 * before it can be used.  Once created, standard FreeRTOS queues and semaphores
 * can be added to the set using calls to xQueueAddToSet().
 * xQueueSelectFromSet() is then used to determine which, if any, of the queues
 * or semaphores contained in the set is in a state where a queue read or
 * semaphore take operation would be successful.
 *
 * Note 1:  See the documentation on http://wwwFreeRTOS.org/RTOS-queue-sets.html
 * for reasons why queue sets are very rarely needed in practice as there are
 * simpler methods of blocking on multiple objects.
 *
 * Note 2:  Blocking on a queue set that contains a mutex will not cause the
 * mutex holder to inherit the priority of the blocked task.
 *
 * Note 3:  An additional 4 bytes of RAM is required for each space in a every
 * queue added to a queue set.  Therefore counting semaphores that have a high
 * maximum count value should not be added to a queue set.
 *
 * Note 4:  A receive (in the case of a queue) or take (in the case of a
 * semaphore) operation must not be performed on a member of a queue set unless
 * a call to xQueueSelectFromSet() has first returned a handle to that set member.
 *
 * @param uxEventQueueLength Queue sets store events that occur on
 * the queues and semaphores contained in the set.  uxEventQueueLength specifies
 * the maximum number of events that can be queued at once.  To be absolutely
 * certain that events are not lost uxEventQueueLength should be set to the
 * total sum of the length of the queues added to the set, where binary
 * semaphores and mutexes have a length of 1, and counting semaphores have a
 * length set by their maximum count value.  Examples:
 *  + If a queue set is to hold a queue of length 5, another queue of length 12,
 *    and a binary semaphore, then uxEventQueueLength should be set to
 *    (5 + 12 + 1), or 18.
 *  + If a queue set is to hold three binary semaphores then uxEventQueueLength
 *    should be set to (1 + 1 + 1 ), or 3.
 *  + If a queue set is to hold a counting semaphore that has a maximum count of
 *    5, and a counting semaphore that has a maximum count of 3, then
 *    uxEventQueueLength should be set to (5 + 3), or 8.
 *
 * @return If the queue set is created successfully then a handle to the created
 * queue set is returned.  Otherwise NULL is returned.
 */
QueueSetHandle_t xQueueCreateSet(const UBaseType_t uxEventQueueLength) PRIVILEGED_FUNCTION;
 
/*
 * Adds a queue or semaphore to a queue set that was previously created by a
 * call to xQueueCreateSet().
 *
 * See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this
 * function.
 *
 * Note 1:  A receive (in the case of a queue) or take (in the case of a
 * semaphore) operation must not be performed on a member of a queue set unless
 * a call to xQueueSelectFromSet() has first returned a handle to that set member.
 *
 * @param xQueueOrSemaphore The handle of the queue or semaphore being added to
 * the queue set (cast to an QueueSetMemberHandle_t type).
 *
 * @param xQueueSet The handle of the queue set to which the queue or semaphore
 * is being added.
 *
 * @return If the queue or semaphore was successfully added to the queue set
 * then pdPASS is returned.  If the queue could not be successfully added to the
 * queue set because it is already a member of a different queue set then pdFAIL
 * is returned.
 */
BaseType_t xQueueAddToSet(QueueSetMemberHandle_t xQueueOrSemaphore, QueueSetHandle_t xQueueSet) PRIVILEGED_FUNCTION;
 
/*
 * Removes a queue or semaphore from a queue set.  A queue or semaphore can only
 * be removed from a set if the queue or semaphore is empty.
 *
 * See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this
 * function.
 *
 * @param xQueueOrSemaphore The handle of the queue or semaphore being removed
 * from the queue set (cast to an QueueSetMemberHandle_t type).
 *
 * @param xQueueSet The handle of the queue set in which the queue or semaphore
 * is included.
 *
 * @return If the queue or semaphore was successfully removed from the queue set
 * then pdPASS is returned.  If the queue was not in the queue set, or the
 * queue (or semaphore) was not empty, then pdFAIL is returned.
 */
BaseType_t xQueueRemoveFromSet(QueueSetMemberHandle_t xQueueOrSemaphore,
                               QueueSetHandle_t       xQueueSet) PRIVILEGED_FUNCTION;
 
/*
 * xQueueSelectFromSet() selects from the members of a queue set a queue or
 * semaphore that either contains data (in the case of a queue) or is available
 * to take (in the case of a semaphore).  xQueueSelectFromSet() effectively
 * allows a task to block (pend) on a read operation on all the queues and
 * semaphores in a queue set simultaneously.
 *
 * See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this
 * function.
 *
 * Note 1:  See the documentation on http://wwwFreeRTOS.org/RTOS-queue-sets.html
 * for reasons why queue sets are very rarely needed in practice as there are
 * simpler methods of blocking on multiple objects.
 *
 * Note 2:  Blocking on a queue set that contains a mutex will not cause the
 * mutex holder to inherit the priority of the blocked task.
 *
 * Note 3:  A receive (in the case of a queue) or take (in the case of a
 * semaphore) operation must not be performed on a member of a queue set unless
 * a call to xQueueSelectFromSet() has first returned a handle to that set member.
 *
 * @param xQueueSet The queue set on which the task will (potentially) block.
 *
 * @param xTicksToWait The maximum time, in ticks, that the calling task will
 * remain in the Blocked state (with other tasks executing) to wait for a member
 * of the queue set to be ready for a successful queue read or semaphore take
 * operation.
 *
 * @return xQueueSelectFromSet() will return the handle of a queue (cast to
 * a QueueSetMemberHandle_t type) contained in the queue set that contains data,
 * or the handle of a semaphore (cast to a QueueSetMemberHandle_t type) contained
 * in the queue set that is available, or NULL if no such queue or semaphore
 * exists before before the specified block time expires.
 */
QueueSetMemberHandle_t xQueueSelectFromSet(QueueSetHandle_t xQueueSet,
                                           const TickType_t xTicksToWait) PRIVILEGED_FUNCTION;
 
/*
 * A version of xQueueSelectFromSet() that can be used from an ISR.
 */
QueueSetMemberHandle_t xQueueSelectFromSetFromISR(QueueSetHandle_t xQueueSet) PRIVILEGED_FUNCTION;
 
/* Not public API functions. */
void        vQueueWaitForMessageRestricted(QueueHandle_t xQueue, TickType_t xTicksToWait,
                                           const BaseType_t xWaitIndefinitely) PRIVILEGED_FUNCTION;
BaseType_t  xQueueGenericReset(QueueHandle_t xQueue, BaseType_t xNewQueue) PRIVILEGED_FUNCTION;
void        vQueueSetQueueNumber(QueueHandle_t xQueue, UBaseType_t uxQueueNumber) PRIVILEGED_FUNCTION;
UBaseType_t uxQueueGetQueueNumber(QueueHandle_t xQueue) PRIVILEGED_FUNCTION;
uint8_t     ucQueueGetQueueType(QueueHandle_t xQueue) PRIVILEGED_FUNCTION;
 
#ifdef __cplusplus
}
#endif
 
#endif /* QUEUE_H */