text: /*
   * FreeRTOS Kernel <DEVELOPMENT BRANCH>
   * Copyright (C) 2021 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
   *
   * SPDX-License-Identifier: MIT
   *
   * 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.
   *
   * 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.
   *
   * https://www.FreeRTOS.org
   * https://github.com/FreeRTOS
   *
   */
  
  
  /*
   * Message buffers build functionality on top of FreeRTOS stream buffers.
   * Whereas stream buffers are used to send a continuous stream of data from one
   * task or interrupt to another, message buffers are used to send variable
   * length discrete messages from one task or interrupt to another.  Their
   * implementation is light weight, making them particularly suited for interrupt
   * to task and core to core communication scenarios.
   *
   * ***NOTE***:  Uniquely among FreeRTOS objects, the stream buffer
   * implementation (so also the message buffer implementation, as message buffers
   * are built on top of stream buffers) assumes there is only one task or
   * interrupt that will write to the buffer (the writer), and only one task or
   * interrupt that will read from the buffer (the reader).  It is safe for the
   * writer and reader to be different tasks or interrupts, but, unlike other
   * FreeRTOS objects, it is not safe to have multiple different writers or
   * multiple different readers.  If there are to be multiple different writers
   * then the application writer must place each call to a writing API function
   * (such as xMessageBufferSend()) inside a critical section and set the send
   * block time to 0.  Likewise, if there are to be multiple different readers
   * then the application writer must place each call to a reading API function
   * (such as xMessageBufferRead()) inside a critical section and set the receive
   * timeout to 0.
   *
   * Message buffers hold variable length messages.  To enable that, when a
   * message is written to the message buffer an additional sizeof( size_t ) bytes
   * are also written to store the message's length (that happens internally, with
   * the API function).  sizeof( size_t ) is typically 4 bytes on a 32-bit
   * architecture, so writing a 10 byte message to a message buffer on a 32-bit
   * architecture will actually reduce the available space in the message buffer
   * by 14 bytes (10 byte are used by the message, and 4 bytes to hold the length
   * of the message).
   */
  
  #ifndef FREERTOS_MESSAGE_BUFFER_H
  #define FREERTOS_MESSAGE_BUFFER_H
  
  #ifndef INC_FREERTOS_H
      #error "include FreeRTOS.h must appear in source files before include message_buffer.h"
  #endif
  
  /* Message buffers are built onto of stream buffers. */
  #include "stream_buffer.h"
  
  /* *INDENT-OFF* */
  #if defined( __cplusplus )
      extern "C" {
  #endif
  /* *INDENT-ON* */
  
  /**
   * Type by which message buffers are referenced.  For example, a call to
   * xMessageBufferCreate() returns an MessageBufferHandle_t variable that can
   * then be used as a parameter to xMessageBufferSend(), xMessageBufferReceive(),
   * etc.
   */
  typedef void * MessageBufferHandle_t;
  
  /*-----------------------------------------------------------*/
  
  /**
   * message_buffer.h
   *
   * <pre>
   * MessageBufferHandle_t xMessageBufferCreate( size_t xBufferSizeBytes );
   * </pre>
   *
   * Creates a new message buffer using dynamically allocated memory.  See
   * xMessageBufferCreateStatic() for a version that uses statically allocated
   * memory (memory that is allocated at compile time).
   *
   * configSUPPORT_DYNAMIC_ALLOCATION must be set to 1 or left undefined in
   * FreeRTOSConfig.h for xMessageBufferCreate() to be available.
   *
   * @param xBufferSizeBytes The total number of bytes (not messages) the message
   * buffer will be able to hold at any one time.  When a message is written to
   * the message buffer an additional sizeof( size_t ) bytes are also written to
   * store the message's length.  sizeof( size_t ) is typically 4 bytes on a
   * 32-bit architecture, so on most 32-bit architectures a 10 byte message will
   * take up 14 bytes of message buffer space.
   *
   * @return If NULL is returned, then the message buffer cannot be created
   * because there is insufficient heap memory available for FreeRTOS to allocate
   * the message buffer data structures and storage area.  A non-NULL value being
   * returned indicates that the message buffer has been created successfully -
   * the returned value should be stored as the handle to the created message
   * buffer.
   *
   * Example use:
   * <pre>
   *
   * void vAFunction( void )
   * {
   * MessageBufferHandle_t xMessageBuffer;
   * const size_t xMessageBufferSizeBytes = 100;
   *
   *  // Create a message buffer that can hold 100 bytes.  The memory used to hold
   *  // both the message buffer structure and the messages themselves is allocated
   *  // dynamically.  Each message added to the buffer consumes an additional 4
   *  // bytes which are used to hold the lengh of the message.
   *  xMessageBuffer = xMessageBufferCreate( xMessageBufferSizeBytes );
   *
   *  if( xMessageBuffer == NULL )
   *  {
   *      // There was not enough heap memory space available to create the
   *      // message buffer.
   *  }
   *  else
   *  {
   *      // The message buffer was created successfully and can now be used.
   *  }
   *
   * </pre>
   * \defgroup xMessageBufferCreate xMessageBufferCreate
   * \ingroup MessageBufferManagement
   */
  #define xMessageBufferCreate( xBufferSizeBytes ) \
      ( MessageBufferHandle_t ) xStreamBufferGenericCreate( xBufferSizeBytes, ( size_t ) 0, pdTRUE )
  
  /**
   * message_buffer.h
   *
   * <pre>
   * MessageBufferHandle_t xMessageBufferCreateStatic( size_t xBufferSizeBytes,
   *                                                uint8_t *pucMessageBufferStorageArea,
   *                                                StaticMessageBuffer_t *pxStaticMessageBuffer );
   * </pre>
   * Creates a new message buffer using statically allocated memory.  See
   * xMessageBufferCreate() for a version that uses dynamically allocated memory.
   *
   * @param xBufferSizeBytes The size, in bytes, of the buffer pointed to by the
   * pucMessageBufferStorageArea parameter.  When a message is written to the
   * message buffer an additional sizeof( size_t ) bytes are also written to store
   * the message's length.  sizeof( size_t ) is typically 4 bytes on a 32-bit
   * architecture, so on most 32-bit architecture a 10 byte message will take up
   * 14 bytes of message buffer space.  The maximum number of bytes that can be
   * stored in the message buffer is actually (xBufferSizeBytes - 1).
   *
   * @param pucMessageBufferStorageArea Must point to a uint8_t array that is at
   * least xBufferSizeBytes + 1 big.  This is the array to which messages are
   * copied when they are written to the message buffer.
   *
   * @param pxStaticMessageBuffer Must point to a variable of type
   * StaticMessageBuffer_t, which will be used to hold the message buffer's data
   * structure.
   *
   * @return If the message buffer is created successfully then a handle to the
   * created message buffer is returned. If either pucMessageBufferStorageArea or
   * pxStaticmessageBuffer are NULL then NULL is returned.
   *
   * Example use:
   * <pre>
   *
   * // Used to dimension the array used to hold the messages.  The available space
   * // will actually be one less than this, so 999.
   #define STORAGE_SIZE_BYTES 1000
   *
   * // Defines the memory that will actually hold the messages within the message
   * // buffer.
   * static uint8_t ucStorageBuffer[ STORAGE_SIZE_BYTES ];
   *
   * // The variable used to hold the message buffer structure.
   * StaticMessageBuffer_t xMessageBufferStruct;
   *
   * void MyFunction( void )
   * {
   * MessageBufferHandle_t xMessageBuffer;
   *
   *  xMessageBuffer = xMessageBufferCreateStatic( sizeof( ucBufferStorage ),
   *                                               ucBufferStorage,
   *                                               &xMessageBufferStruct );
   *
   *  // As neither the pucMessageBufferStorageArea or pxStaticMessageBuffer
   *  // parameters were NULL, xMessageBuffer will not be NULL, and can be used to
   *  // reference the created message buffer in other message buffer API calls.
   *
   *  // Other code that uses the message buffer can go here.
   * }
   *
   * </pre>
   * \defgroup xMessageBufferCreateStatic xMessageBufferCreateStatic
   * \ingroup MessageBufferManagement
   */
  #define xMessageBufferCreateStatic( xBufferSizeBytes, pucMessageBufferStorageArea, pxStaticMessageBuffer ) \
      ( MessageBufferHandle_t ) xStreamBufferGenericCreateStatic( xBufferSizeBytes, 0, pdTRUE, pucMessageBufferStorageArea, pxStaticMessageBuffer )
  
  /**
   * message_buffer.h
   *
   * <pre>
   * size_t xMessageBufferSend( MessageBufferHandle_t xMessageBuffer,
   *                         const void *pvTxData,
   *                         size_t xDataLengthBytes,
   *                         TickType_t xTicksToWait );
   * </pre>
   *
   * Sends a discrete message to the message buffer.  The message can be any
   * length that fits within the buffer's free space, and is copied into the
   * buffer.
   *
   * ***NOTE***:  Uniquely among FreeRTOS objects, the stream buffer
   * implementation (so also the message buffer implementation, as message buffers
   * are built on top of stream buffers) assumes there is only one task or
   * interrupt that will write to the buffer (the writer), and only one task or
   * interrupt that will read from the buffer (the reader).  It is safe for the
   * writer and reader to be different tasks or interrupts, but, unlike other
   * FreeRTOS objects, it is not safe to have multiple different writers or
   * multiple different readers.  If there are to be multiple different writers
   * then the application writer must place each call to a writing API function
   * (such as xMessageBufferSend()) inside a critical section and set the send
   * block time to 0.  Likewise, if there are to be multiple different readers
   * then the application writer must place each call to a reading API function
   * (such as xMessageBufferRead()) inside a critical section and set the receive
   * block time to 0.
   *
   * Use xMessageBufferSend() to write to a message buffer from a task.  Use
   * xMessageBufferSendFromISR() to write to a message buffer from an interrupt
   * service routine (ISR).
   *
   * @param xMessageBuffer The handle of the message buffer to which a message is
   * being sent.
   *
   * @param pvTxData A pointer to the message that is to be copied into the
   * message buffer.
   *
   * @param xDataLengthBytes The length of the message.  That is, the number of
   * bytes to copy from pvTxData into the message buffer.  When a message is
   * written to the message buffer an additional sizeof( size_t ) bytes are also
   * written to store the message's length.  sizeof( size_t ) is typically 4 bytes
   * on a 32-bit architecture, so on most 32-bit architecture setting
   * xDataLengthBytes to 20 will reduce the free space in the message buffer by 24
   * bytes (20 bytes of message data and 4 bytes to hold the message length).
   *
   * @param xTicksToWait The maximum amount of time the calling task should remain
   * in the Blocked state to wait for enough space to become available in the
   * message buffer, should the message buffer have insufficient space when
   * xMessageBufferSend() is called.  The calling task will never block if
   * xTicksToWait is zero.  The block time is specified in tick periods, so the
   * absolute time it represents is dependent on the tick frequency.  The macro
   * pdMS_TO_TICKS() can be used to convert a time specified in milliseconds into
   * a time specified in ticks.  Setting xTicksToWait to portMAX_DELAY will cause
   * the task to wait indefinitely (without timing out), provided
   * INCLUDE_vTaskSuspend is set to 1 in FreeRTOSConfig.h.  Tasks do not use any
   * CPU time when they are in the Blocked state.
   *
   * @return The number of bytes written to the message buffer.  If the call to
   * xMessageBufferSend() times out before there was enough space to write the
   * message into the message buffer then zero is returned.  If the call did not
   * time out then xDataLengthBytes is returned.
   *
   * Example use:
   * <pre>
   * void vAFunction( MessageBufferHandle_t xMessageBuffer )
   * {
   * size_t xBytesSent;
   * uint8_t ucArrayToSend[] = { 0, 1, 2, 3 };
   * char *pcStringToSend = "String to send";
   * const TickType_t x100ms = pdMS_TO_TICKS( 100 );
   *
   *  // Send an array to the message buffer, blocking for a maximum of 100ms to
   *  // wait for enough space to be available in the message buffer.
   *  xBytesSent = xMessageBufferSend( xMessageBuffer, ( void * ) ucArrayToSend, sizeof( ucArrayToSend ), x100ms );
   *
   *  if( xBytesSent != sizeof( ucArrayToSend ) )
   *  {
   *      // The call to xMessageBufferSend() times out before there was enough
   *      // space in the buffer for the data to be written.
   *  }
   *
   *  // Send the string to the message buffer.  Return immediately if there is
   *  // not enough space in the buffer.
   *  xBytesSent = xMessageBufferSend( xMessageBuffer, ( void * ) pcStringToSend, strlen( pcStringToSend ), 0 );
   *
   *  if( xBytesSent != strlen( pcStringToSend ) )
   *  {
   *      // The string could not be added to the message buffer because there was
   *      // not enough free space in the buffer.
   *  }
   * }
   * </pre>
   * \defgroup xMessageBufferSend xMessageBufferSend
   * \ingroup MessageBufferManagement
   */
  #define xMessageBufferSend( xMessageBuffer, pvTxData, xDataLengthBytes, xTicksToWait ) \
      xStreamBufferSend( ( StreamBufferHandle_t ) xMessageBuffer, pvTxData, xDataLengthBytes, xTicksToWait )
  
  /**
   * message_buffer.h
   *
   * <pre>
   * size_t xMessageBufferSendFromISR( MessageBufferHandle_t xMessageBuffer,
   *                                const void *pvTxData,
   *                                size_t xDataLengthBytes,
   *                                BaseType_t *pxHigherPriorityTaskWoken );
   * </pre>
   *
   * Interrupt safe version of the API function that sends a discrete message to
   * the message buffer.  The message can be any length that fits within the
   * buffer's free space, and is copied into the buffer.
   *
   * ***NOTE***:  Uniquely among FreeRTOS objects, the stream buffer
   * implementation (so also the message buffer implementation, as message buffers
   * are built on top of stream buffers) assumes there is only one task or
   * interrupt that will write to the buffer (the writer), and only one task or
   * interrupt that will read from the buffer (the reader).  It is safe for the
   * writer and reader to be different tasks or interrupts, but, unlike other
   * FreeRTOS objects, it is not safe to have multiple different writers or
   * multiple different readers.  If there are to be multiple different writers
   * then the application writer must place each call to a writing API function
   * (such as xMessageBufferSend()) inside a critical section and set the send
   * block time to 0.  Likewise, if there are to be multiple different readers
   * then the application writer must place each call to a reading API function
   * (such as xMessageBufferRead()) inside a critical section and set the receive
   * block time to 0.
   *
   * Use xMessageBufferSend() to write to a message buffer from a task.  Use
   * xMessageBufferSendFromISR() to write to a message buffer from an interrupt
   * service routine (ISR).
   *
   * @param xMessageBuffer The handle of the message buffer to which a message is
   * being sent.
   *
   * @param pvTxData A pointer to the message that is to be copied into the
   * message buffer.
   *
   * @param xDataLengthBytes The length of the message.  That is, the number of
   * bytes to copy from pvTxData into the message buffer.  When a message is
   * written to the message buffer an additional sizeof( size_t ) bytes are also
   * written to store the message's length.  sizeof( size_t ) is typically 4 bytes
   * on a 32-bit architecture, so on most 32-bit architecture setting
   * xDataLengthBytes to 20 will reduce the free space in the message buffer by 24
   * bytes (20 bytes of message data and 4 bytes to hold the message length).
   *
   * @param pxHigherPriorityTaskWoken  It is possible that a message buffer will
   * have a task blocked on it waiting for data.  Calling
   * xMessageBufferSendFromISR() can make data available, and so cause a task that
   * was waiting for data to leave the Blocked state.  If calling
   * xMessageBufferSendFromISR() causes a task to leave the Blocked state, and the
   * unblocked task has a priority higher than the currently executing task (the
   * task that was interrupted), then, internally, xMessageBufferSendFromISR()
   * will set *pxHigherPriorityTaskWoken to pdTRUE.  If
   * xMessageBufferSendFromISR() sets this value to pdTRUE, then normally a
   * context switch should be performed before the interrupt is exited.  This will
   * ensure that the interrupt returns directly to the highest priority Ready
   * state task.  *pxHigherPriorityTaskWoken should be set to pdFALSE before it
   * is passed into the function.  See the code example below for an example.
   *
   * @return The number of bytes actually written to the message buffer.  If the
   * message buffer didn't have enough free space for the message to be stored
   * then 0 is returned, otherwise xDataLengthBytes is returned.
   *
   * Example use:
   * <pre>
   * // A message buffer that has already been created.
   * MessageBufferHandle_t xMessageBuffer;
   *
   * void vAnInterruptServiceRoutine( void )
   * {
   * size_t xBytesSent;
   * char *pcStringToSend = "String to send";
   * BaseType_t xHigherPriorityTaskWoken = pdFALSE; // Initialised to pdFALSE.
   *
   *  // Attempt to send the string to the message buffer.
   *  xBytesSent = xMessageBufferSendFromISR( xMessageBuffer,
   *                                          ( void * ) pcStringToSend,
   *                                          strlen( pcStringToSend ),
   *                                          &xHigherPriorityTaskWoken );
   *
   *  if( xBytesSent != strlen( pcStringToSend ) )
   *  {
   *      // The string could not be added to the message buffer because there was
   *      // not enough free space in the buffer.
   *  }
   *
   *  // If xHigherPriorityTaskWoken was set to pdTRUE inside
   *  // xMessageBufferSendFromISR() then a task that has a priority above the
   *  // priority of the currently executing task was unblocked and a context
   *  // switch should be performed to ensure the ISR returns to the unblocked
   *  // task.  In most FreeRTOS ports this is done by simply passing
   *  // xHigherPriorityTaskWoken into portYIELD_FROM_ISR(), which will test the
   *  // variables value, and perform the context switch if necessary.  Check the
   *  // documentation for the port in use for port specific instructions.
   *  portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
   * }
   * </pre>
   * \defgroup xMessageBufferSendFromISR xMessageBufferSendFromISR
   * \ingroup MessageBufferManagement
   */
  #define xMessageBufferSendFromISR( xMessageBuffer, pvTxData, xDataLengthBytes, pxHigherPriorityTaskWoken ) \
      xStreamBufferSendFromISR( ( StreamBufferHandle_t ) xMessageBuffer, pvTxData, xDataLengthBytes, pxHigherPriorityTaskWoken )
  
  /**
   * message_buffer.h
   *
   * <pre>
   * size_t xMessageBufferReceive( MessageBufferHandle_t xMessageBuffer,
   *                            void *pvRxData,
   *                            size_t xBufferLengthBytes,
   *                            TickType_t xTicksToWait );
   * </pre>
   *
   * Receives a discrete message from a message buffer.  Messages can be of
   * variable length and are copied out of the buffer.
   *
   * ***NOTE***:  Uniquely among FreeRTOS objects, the stream buffer
   * implementation (so also the message buffer implementation, as message buffers
   * are built on top of stream buffers) assumes there is only one task or
   * interrupt that will write to the buffer (the writer), and only one task or
   * interrupt that will read from the buffer (the reader).  It is safe for the
   * writer and reader to be different tasks or interrupts, but, unlike other
   * FreeRTOS objects, it is not safe to have multiple different writers or
   * multiple different readers.  If there are to be multiple different writers
   * then the application writer must place each call to a writing API function
   * (such as xMessageBufferSend()) inside a critical section and set the send
   * block time to 0.  Likewise, if there are to be multiple different readers
   * then the application writer must place each call to a reading API function
   * (such as xMessageBufferRead()) inside a critical section and set the receive
   * block time to 0.
   *
   * Use xMessageBufferReceive() to read from a message buffer from a task.  Use
   * xMessageBufferReceiveFromISR() to read from a message buffer from an
   * interrupt service routine (ISR).
   *
   * @param xMessageBuffer The handle of the message buffer from which a message
   * is being received.
   *
   * @param pvRxData A pointer to the buffer into which the received message is
   * to be copied.
   *
   * @param xBufferLengthBytes The length of the buffer pointed to by the pvRxData
   * parameter.  This sets the maximum length of the message that can be received.
   * If xBufferLengthBytes is too small to hold the next message then the message
   * will be left in the message buffer and 0 will be returned.
   *
   * @param xTicksToWait The maximum amount of time the task should remain in the
   * Blocked state to wait for a message, should the message buffer be empty.
   * xMessageBufferReceive() will return immediately if xTicksToWait is zero and
   * the message buffer is empty.  The block time is specified in tick periods, so
   * the absolute time it represents is dependent on the tick frequency.  The
   * macro pdMS_TO_TICKS() can be used to convert a time specified in milliseconds
   * into a time specified in ticks.  Setting xTicksToWait to portMAX_DELAY will
   * cause the task to wait indefinitely (without timing out), provided
   * INCLUDE_vTaskSuspend is set to 1 in FreeRTOSConfig.h.  Tasks do not use any
   * CPU time when they are in the Blocked state.
   *
   * @return The length, in bytes, of the message read from the message buffer, if
   * any.  If xMessageBufferReceive() times out before a message became available
   * then zero is returned.  If the length of the message is greater than
   * xBufferLengthBytes then the message will be left in the message buffer and
   * zero is returned.
   *
   * Example use:
   * <pre>
   * void vAFunction( MessageBuffer_t xMessageBuffer )
   * {
   * uint8_t ucRxData[ 20 ];
   * size_t xReceivedBytes;
   * const TickType_t xBlockTime = pdMS_TO_TICKS( 20 );
   *
   *  // Receive the next message from the message buffer.  Wait in the Blocked
   *  // state (so not using any CPU processing time) for a maximum of 100ms for
   *  // a message to become available.
   *  xReceivedBytes = xMessageBufferReceive( xMessageBuffer,
   *                                          ( void * ) ucRxData,
   *                                          sizeof( ucRxData ),
   *                                          xBlockTime );
   *
   *  if( xReceivedBytes > 0 )
   *  {
   *      // A ucRxData contains a message that is xReceivedBytes long.  Process
   *      // the message here....
   *  }
   * }
   * </pre>
   * \defgroup xMessageBufferReceive xMessageBufferReceive
   * \ingroup MessageBufferManagement
   */
  #define xMessageBufferReceive( xMessageBuffer, pvRxData, xBufferLengthBytes, xTicksToWait ) \
      xStreamBufferReceive( ( StreamBufferHandle_t ) xMessageBuffer, pvRxData, xBufferLengthBytes, xTicksToWait )
  
  
  /**
   * message_buffer.h
   *
   * <pre>
   * size_t xMessageBufferReceiveFromISR( MessageBufferHandle_t xMessageBuffer,
   *                                   void *pvRxData,
   *                                   size_t xBufferLengthBytes,
   *                                   BaseType_t *pxHigherPriorityTaskWoken );
   * </pre>
   *
   * An interrupt safe version of the API function that receives a discrete
   * message from a message buffer.  Messages can be of variable length and are
   * copied out of the buffer.
   *
   * ***NOTE***:  Uniquely among FreeRTOS objects, the stream buffer
   * implementation (so also the message buffer implementation, as message buffers
   * are built on top of stream buffers) assumes there is only one task or
   * interrupt that will write to the buffer (the writer), and only one task or
   * interrupt that will read from the buffer (the reader).  It is safe for the
   * writer and reader to be different tasks or interrupts, but, unlike other
   * FreeRTOS objects, it is not safe to have multiple different writers or
   * multiple different readers.  If there are to be multiple different writers
   * then the application writer must place each call to a writing API function
   * (such as xMessageBufferSend()) inside a critical section and set the send
   * block time to 0.  Likewise, if there are to be multiple different readers
   * then the application writer must place each call to a reading API function
   * (such as xMessageBufferRead()) inside a critical section and set the receive
   * block time to 0.
   *
   * Use xMessageBufferReceive() to read from a message buffer from a task.  Use
   * xMessageBufferReceiveFromISR() to read from a message buffer from an
   * interrupt service routine (ISR).
   *
   * @param xMessageBuffer The handle of the message buffer from which a message
   * is being received.
   *
   * @param pvRxData A pointer to the buffer into which the received message is
   * to be copied.
   *
   * @param xBufferLengthBytes The length of the buffer pointed to by the pvRxData
   * parameter.  This sets the maximum length of the message that can be received.
   * If xBufferLengthBytes is too small to hold the next message then the message
   * will be left in the message buffer and 0 will be returned.
   *
   * @param pxHigherPriorityTaskWoken  It is possible that a message buffer will
   * have a task blocked on it waiting for space to become available.  Calling
   * xMessageBufferReceiveFromISR() can make space available, and so cause a task
   * that is waiting for space to leave the Blocked state.  If calling
   * xMessageBufferReceiveFromISR() causes a task to leave the Blocked state, and
   * the unblocked task has a priority higher than the currently executing task
   * (the task that was interrupted), then, internally,
   * xMessageBufferReceiveFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE.
   * If xMessageBufferReceiveFromISR() sets this value to pdTRUE, then normally a
   * context switch should be performed before the interrupt is exited.  That will
   * ensure the interrupt returns directly to the highest priority Ready state
   * task.  *pxHigherPriorityTaskWoken should be set to pdFALSE before it is
   * passed into the function.  See the code example below for an example.
   *
   * @return The length, in bytes, of the message read from the message buffer, if
   * any.
   *
   * Example use:
   * <pre>
   * // A message buffer that has already been created.
   * MessageBuffer_t xMessageBuffer;
   *
   * void vAnInterruptServiceRoutine( void )
   * {
   * uint8_t ucRxData[ 20 ];
   * size_t xReceivedBytes;
   * BaseType_t xHigherPriorityTaskWoken = pdFALSE;  // Initialised to pdFALSE.
   *
   *  // Receive the next message from the message buffer.
   *  xReceivedBytes = xMessageBufferReceiveFromISR( xMessageBuffer,
   *                                                ( void * ) ucRxData,
   *                                                sizeof( ucRxData ),
   *                                                &xHigherPriorityTaskWoken );
   *
   *  if( xReceivedBytes > 0 )
   *  {
   *      // A ucRxData contains a message that is xReceivedBytes long.  Process
   *      // the message here....
   *  }
   *
   *  // If xHigherPriorityTaskWoken was set to pdTRUE inside
   *  // xMessageBufferReceiveFromISR() then a task that has a priority above the
   *  // priority of the currently executing task was unblocked and a context
   *  // switch should be performed to ensure the ISR returns to the unblocked
   *  // task.  In most FreeRTOS ports this is done by simply passing
   *  // xHigherPriorityTaskWoken into portYIELD_FROM_ISR(), which will test the
   *  // variables value, and perform the context switch if necessary.  Check the
   *  // documentation for the port in use for port specific instructions.
   *  portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
   * }
   * </pre>
   * \defgroup xMessageBufferReceiveFromISR xMessageBufferReceiveFromISR
   * \ingroup MessageBufferManagement
   */
  #define xMessageBufferReceiveFromISR( xMessageBuffer, pvRxData, xBufferLengthBytes, pxHigherPriorityTaskWoken ) \
      xStreamBufferReceiveFromISR( ( StreamBufferHandle_t ) xMessageBuffer, pvRxData, xBufferLengthBytes, pxHigherPriorityTaskWoken )
  
  /**
   * message_buffer.h
   *
   * <pre>
   * void vMessageBufferDelete( MessageBufferHandle_t xMessageBuffer );
   * </pre>
   *
   * Deletes a message buffer that was previously created using a call to
   * xMessageBufferCreate() or xMessageBufferCreateStatic().  If the message
   * buffer was created using dynamic memory (that is, by xMessageBufferCreate()),
   * then the allocated memory is freed.
   *
   * A message buffer handle must not be used after the message buffer has been
   * deleted.
   *
   * @param xMessageBuffer The handle of the message buffer to be deleted.
   *
   */
  #define vMessageBufferDelete( xMessageBuffer ) \
      vStreamBufferDelete( ( StreamBufferHandle_t ) xMessageBuffer )
  
  /**
   * message_buffer.h
   * <pre>
   * BaseType_t xMessageBufferIsFull( MessageBufferHandle_t xMessageBuffer );
   * </pre>
   *
   * Tests to see if a message buffer is full.  A message buffer is full if it
   * cannot accept any more messages, of any size, until space is made available
   * by a message being removed from the message buffer.
   *
   * @param xMessageBuffer The handle of the message buffer being queried.
   *
   * @return If the message buffer referenced by xMessageBuffer is full then
   * pdTRUE is returned.  Otherwise pdFALSE is returned.
   */
  #define xMessageBufferIsFull( xMessageBuffer ) \
      xStreamBufferIsFull( ( StreamBufferHandle_t ) xMessageBuffer )
  
  /**
   * message_buffer.h
   * <pre>
   * BaseType_t xMessageBufferIsEmpty( MessageBufferHandle_t xMessageBuffer );
   * </pre>
   *
   * Tests to see if a message buffer is empty (does not contain any messages).
   *
   * @param xMessageBuffer The handle of the message buffer being queried.
   *
   * @return If the message buffer referenced by xMessageBuffer is empty then
   * pdTRUE is returned.  Otherwise pdFALSE is returned.
   *
   */
  #define xMessageBufferIsEmpty( xMessageBuffer ) \
      xStreamBufferIsEmpty( ( StreamBufferHandle_t ) xMessageBuffer )
  
  /**
   * message_buffer.h
   * <pre>
   * BaseType_t xMessageBufferReset( MessageBufferHandle_t xMessageBuffer );
   * </pre>
   *
   * Resets a message buffer to its initial empty state, discarding any message it
   * contained.
   *
   * A message buffer can only be reset if there are no tasks blocked on it.
   *
   * @param xMessageBuffer The handle of the message buffer being reset.
   *
   * @return If the message buffer was reset then pdPASS is returned.  If the
   * message buffer could not be reset because either there was a task blocked on
   * the message queue to wait for space to become available, or to wait for a
   * a message to be available, then pdFAIL is returned.
   *
   * \defgroup xMessageBufferReset xMessageBufferReset
   * \ingroup MessageBufferManagement
   */
  #define xMessageBufferReset( xMessageBuffer ) \
      xStreamBufferReset( ( StreamBufferHandle_t ) xMessageBuffer )
  
  
  /**
   * message_buffer.h
   * <pre>
   * size_t xMessageBufferSpaceAvailable( MessageBufferHandle_t xMessageBuffer );
   * </pre>
   * Returns the number of bytes of free space in the message buffer.
   *
   * @param xMessageBuffer The handle of the message buffer being queried.
   *
   * @return The number of bytes that can be written to the message buffer before
   * the message buffer would be full.  When a message is written to the message
   * buffer an additional sizeof( size_t ) bytes are also written to store the
   * message's length.  sizeof( size_t ) is typically 4 bytes on a 32-bit
   * architecture, so if xMessageBufferSpacesAvailable() returns 10, then the size
   * of the largest message that can be written to the message buffer is 6 bytes.
   *
   * \defgroup xMessageBufferSpaceAvailable xMessageBufferSpaceAvailable
   * \ingroup MessageBufferManagement
   */
  #define xMessageBufferSpaceAvailable( xMessageBuffer ) \
      xStreamBufferSpacesAvailable( ( StreamBufferHandle_t ) xMessageBuffer )
  #define xMessageBufferSpacesAvailable( xMessageBuffer ) \
      xStreamBufferSpacesAvailable( ( StreamBufferHandle_t ) xMessageBuffer ) /* Corrects typo in original macro name. */
  
  /**
   * message_buffer.h
   * <pre>
   * size_t xMessageBufferNextLengthBytes( MessageBufferHandle_t xMessageBuffer );
   * </pre>
   * Returns the length (in bytes) of the next message in a message buffer.
   * Useful if xMessageBufferReceive() returned 0 because the size of the buffer
   * passed into xMessageBufferReceive() was too small to hold the next message.
   *
   * @param xMessageBuffer The handle of the message buffer being queried.
   *
   * @return The length (in bytes) of the next message in the message buffer, or 0
   * if the message buffer is empty.
   *
   * \defgroup xMessageBufferNextLengthBytes xMessageBufferNextLengthBytes
   * \ingroup MessageBufferManagement
   */
  #define xMessageBufferNextLengthBytes( xMessageBuffer ) \
      xStreamBufferNextMessageLengthBytes( ( StreamBufferHandle_t ) xMessageBuffer ) PRIVILEGED_FUNCTION;
  
  /**
   * message_buffer.h
   *
   * <pre>
   * BaseType_t xMessageBufferSendCompletedFromISR( MessageBufferHandle_t xMessageBuffer, BaseType_t *pxHigherPriorityTaskWoken );
   * </pre>
   *
   * For advanced users only.
   *
   * The sbSEND_COMPLETED() macro is called from within the FreeRTOS APIs when
   * data is sent to a message buffer or stream buffer.  If there was a task that
   * was blocked on the message or stream buffer waiting for data to arrive then
   * the sbSEND_COMPLETED() macro sends a notification to the task to remove it
   * from the Blocked state.  xMessageBufferSendCompletedFromISR() does the same
   * thing.  It is provided to enable application writers to implement their own
   * version of sbSEND_COMPLETED(), and MUST NOT BE USED AT ANY OTHER TIME.
   *
   * See the example implemented in FreeRTOS/Demo/Minimal/MessageBufferAMP.c for
   * additional information.
   *
   * @param xMessageBuffer The handle of the stream buffer to which data was
   * written.
   *
   * @param pxHigherPriorityTaskWoken *pxHigherPriorityTaskWoken should be
   * initialised to pdFALSE before it is passed into
   * xMessageBufferSendCompletedFromISR().  If calling
   * xMessageBufferSendCompletedFromISR() removes a task from the Blocked state,
   * and the task has a priority above the priority of the currently running task,
   * then *pxHigherPriorityTaskWoken will get set to pdTRUE indicating that a
   * context switch should be performed before exiting the ISR.
   *
   * @return If a task was removed from the Blocked state then pdTRUE is returned.
   * Otherwise pdFALSE is returned.
   *
   * \defgroup xMessageBufferSendCompletedFromISR xMessageBufferSendCompletedFromISR
   * \ingroup StreamBufferManagement
   */
  #define xMessageBufferSendCompletedFromISR( xMessageBuffer, pxHigherPriorityTaskWoken ) \
      xStreamBufferSendCompletedFromISR( ( StreamBufferHandle_t ) xMessageBuffer, pxHigherPriorityTaskWoken )
  
  /**
   * message_buffer.h
   *
   * <pre>
   * BaseType_t xMessageBufferReceiveCompletedFromISR( MessageBufferHandle_t xMessageBuffer, BaseType_t *pxHigherPriorityTaskWoken );
   * </pre>
   *
   * For advanced users only.
   *
   * The sbRECEIVE_COMPLETED() macro is called from within the FreeRTOS APIs when
   * data is read out of a message buffer or stream buffer.  If there was a task
   * that was blocked on the message or stream buffer waiting for data to arrive
   * then the sbRECEIVE_COMPLETED() macro sends a notification to the task to
   * remove it from the Blocked state.  xMessageBufferReceiveCompletedFromISR()
   * does the same thing.  It is provided to enable application writers to
   * implement their own version of sbRECEIVE_COMPLETED(), and MUST NOT BE USED AT
   * ANY OTHER TIME.
   *
   * See the example implemented in FreeRTOS/Demo/Minimal/MessageBufferAMP.c for
   * additional information.
   *
   * @param xMessageBuffer The handle of the stream buffer from which data was
   * read.
   *
   * @param pxHigherPriorityTaskWoken *pxHigherPriorityTaskWoken should be
   * initialised to pdFALSE before it is passed into
   * xMessageBufferReceiveCompletedFromISR().  If calling
   * xMessageBufferReceiveCompletedFromISR() removes a task from the Blocked state,
   * and the task has a priority above the priority of the currently running task,
   * then *pxHigherPriorityTaskWoken will get set to pdTRUE indicating that a
   * context switch should be performed before exiting the ISR.
   *
   * @return If a task was removed from the Blocked state then pdTRUE is returned.
   * Otherwise pdFALSE is returned.
   *
   * \defgroup xMessageBufferReceiveCompletedFromISR xMessageBufferReceiveCompletedFromISR
   * \ingroup StreamBufferManagement
   */
  #define xMessageBufferReceiveCompletedFromISR( xMessageBuffer, pxHigherPriorityTaskWoken ) \
      xStreamBufferReceiveCompletedFromISR( ( StreamBufferHandle_t ) xMessageBuffer, pxHigherPriorityTaskWoken )
  
  /* *INDENT-OFF* */
  #if defined( __cplusplus )
      } /* extern "C" */
  #endif
  /* *INDENT-ON* */
  
  #endif /* !defined( FREERTOS_MESSAGE_BUFFER_H ) */
  