include/croutine.h

/*
 * FreeRTOS Kernel V10.3.1
 * Copyright (C) 2020 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
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 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
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 *
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 */

#ifndef CO_ROUTINE_H
    #define CO_ROUTINE_H

    #ifndef INC_FREERTOS_H
        #error "include FreeRTOS.h must appear in source files before include croutine.h"
    #endif

    #include "list.h"

    #ifdef __cplusplus
        extern "C" {
    #endif

/* Used to hide the implementation of the co-routine control block.  The
 * control block structure however has to be included in the header due to
 * the macro implementation of the co-routine functionality. */
    typedef void * CoRoutineHandle_t;

/* Defines the prototype to which co-routine functions must conform. */
    typedef void (* crCOROUTINE_CODE)( CoRoutineHandle_t,
                                       UBaseType_t );

    typedef struct corCoRoutineControlBlock
    {
        crCOROUTINE_CODE pxCoRoutineFunction;
        ListItem_t xGenericListItem; /*< List item used to place the CRCB in ready and blocked queues. */
        ListItem_t xEventListItem;   /*< List item used to place the CRCB in event lists. */
        UBaseType_t uxPriority;      /*< The priority of the co-routine in relation to other co-routines. */
        UBaseType_t uxIndex;         /*< Used to distinguish between co-routines when multiple co-routines use the same co-routine function. */
        uint16_t uxState;            /*< Used internally by the co-routine implementation. */
    } CRCB_t;                        /* Co-routine control block.  Note must be identical in size down to uxPriority with TCB_t. */

/**
 * croutine. h
 *<pre>
 * BaseType_t xCoRoutineCreate(
 *                               crCOROUTINE_CODE pxCoRoutineCode,
 *                               UBaseType_t uxPriority,
 *                               UBaseType_t uxIndex
 *                             );</pre>
 *
 * Create a new co-routine and add it to the list of co-routines that are
 * ready to run.
 *
 * @param pxCoRoutineCode Pointer to the co-routine function.  Co-routine
 * functions require special syntax - see the co-routine section of the WEB
 * documentation for more information.
 *
 * @param uxPriority The priority with respect to other co-routines at which
 *  the co-routine will run.
 *
 * @param uxIndex Used to distinguish between different co-routines that
 * execute the same function.  See the example below and the co-routine section
 * of the WEB documentation for further information.
 *
 * @return pdPASS if the co-routine was successfully created and added to a ready
 * list, otherwise an error code defined with ProjDefs.h.
 *
 * Example usage:
 * <pre>
 * // Co-routine to be created.
 * void vFlashCoRoutine( CoRoutineHandle_t xHandle, UBaseType_t uxIndex )
 * {
 * // Variables in co-routines must be declared static if they must maintain value across a blocking call.
 * // This may not be necessary for const variables.
 * static const char cLedToFlash[ 2 ] = { 5, 6 };
 * static const TickType_t uxFlashRates[ 2 ] = { 200, 400 };
 *
 *   // Must start every co-routine with a call to crSTART();
 *   crSTART( xHandle );
 *
 *   for( ;; )
 *   {
 *       // This co-routine just delays for a fixed period, then toggles
 *       // an LED.  Two co-routines are created using this function, so
 *       // the uxIndex parameter is used to tell the co-routine which
 *       // LED to flash and how int32_t to delay.  This assumes xQueue has
 *       // already been created.
 *       vParTestToggleLED( cLedToFlash[ uxIndex ] );
 *       crDELAY( xHandle, uxFlashRates[ uxIndex ] );
 *   }
 *
 *   // Must end every co-routine with a call to crEND();
 *   crEND();
 * }
 *
 * // Function that creates two co-routines.
 * void vOtherFunction( void )
 * {
 * uint8_t ucParameterToPass;
 * TaskHandle_t xHandle;
 *
 *   // Create two co-routines at priority 0.  The first is given index 0
 *   // so (from the code above) toggles LED 5 every 200 ticks.  The second
 *   // is given index 1 so toggles LED 6 every 400 ticks.
 *   for( uxIndex = 0; uxIndex < 2; uxIndex++ )
 *   {
 *       xCoRoutineCreate( vFlashCoRoutine, 0, uxIndex );
 *   }
 * }
 * </pre>
 * \defgroup xCoRoutineCreate xCoRoutineCreate
 * \ingroup Tasks
 */
    BaseType_t xCoRoutineCreate( crCOROUTINE_CODE pxCoRoutineCode,
                                 UBaseType_t uxPriority,
                                 UBaseType_t uxIndex );


/**
 * croutine. h
 *<pre>
 * void vCoRoutineSchedule( void );</pre>
 *
 * Run a co-routine.
 *
 * vCoRoutineSchedule() executes the highest priority co-routine that is able
 * to run.  The co-routine will execute until it either blocks, yields or is
 * preempted by a task.  Co-routines execute cooperatively so one
 * co-routine cannot be preempted by another, but can be preempted by a task.
 *
 * If an application comprises of both tasks and co-routines then
 * vCoRoutineSchedule should be called from the idle task (in an idle task
 * hook).
 *
 * Example usage:
 * <pre>
 * // This idle task hook will schedule a co-routine each time it is called.
 * // The rest of the idle task will execute between co-routine calls.
 * void vApplicationIdleHook( void )
 * {
 *  vCoRoutineSchedule();
 * }
 *
 * // Alternatively, if you do not require any other part of the idle task to
 * // execute, the idle task hook can call vCoRoutineSchedule() within an
 * // infinite loop.
 * void vApplicationIdleHook( void )
 * {
 *  for( ;; )
 *  {
 *      vCoRoutineSchedule();
 *  }
 * }
 * </pre>
 * \defgroup vCoRoutineSchedule vCoRoutineSchedule
 * \ingroup Tasks
 */
    void vCoRoutineSchedule( void );

/**
 * croutine. h
 * <pre>
 * crSTART( CoRoutineHandle_t xHandle );</pre>
 *
 * This macro MUST always be called at the start of a co-routine function.
 *
 * Example usage:
 * <pre>
 * // Co-routine to be created.
 * void vACoRoutine( CoRoutineHandle_t xHandle, UBaseType_t uxIndex )
 * {
 * // Variables in co-routines must be declared static if they must maintain value across a blocking call.
 * static int32_t ulAVariable;
 *
 *   // Must start every co-routine with a call to crSTART();
 *   crSTART( xHandle );
 *
 *   for( ;; )
 *   {
 *        // Co-routine functionality goes here.
 *   }
 *
 *   // Must end every co-routine with a call to crEND();
 *   crEND();
 * }</pre>
 * \defgroup crSTART crSTART
 * \ingroup Tasks
 */
    #define crSTART( pxCRCB )                        \
    switch( ( ( CRCB_t * ) ( pxCRCB ) )->uxState ) { \
        case 0:

/**
 * croutine. h
 * <pre>
 * crEND();</pre>
 *
 * This macro MUST always be called at the end of a co-routine function.
 *
 * Example usage:
 * <pre>
 * // Co-routine to be created.
 * void vACoRoutine( CoRoutineHandle_t xHandle, UBaseType_t uxIndex )
 * {
 * // Variables in co-routines must be declared static if they must maintain value across a blocking call.
 * static int32_t ulAVariable;
 *
 *   // Must start every co-routine with a call to crSTART();
 *   crSTART( xHandle );
 *
 *   for( ;; )
 *   {
 *        // Co-routine functionality goes here.
 *   }
 *
 *   // Must end every co-routine with a call to crEND();
 *   crEND();
 * }</pre>
 * \defgroup crSTART crSTART
 * \ingroup Tasks
 */
    #define crEND()    }

/*
 * These macros are intended for internal use by the co-routine implementation
 * only.  The macros should not be used directly by application writers.
 */
    #define crSET_STATE0( xHandle )                                   \
    ( ( CRCB_t * ) ( xHandle ) )->uxState = ( __LINE__ * 2 ); return; \
    case ( __LINE__ * 2 ):
    #define crSET_STATE1( xHandle )                                           \
    ( ( CRCB_t * ) ( xHandle ) )->uxState = ( ( __LINE__ * 2 ) + 1 ); return; \
    case ( ( __LINE__ * 2 ) + 1 ):

/**
 * croutine. h
 *<pre>
 * crDELAY( CoRoutineHandle_t xHandle, TickType_t xTicksToDelay );</pre>
 *
 * Delay a co-routine for a fixed period of time.
 *
 * crDELAY can only be called from the co-routine function itself - not
 * from within a function called by the co-routine function.  This is because
 * co-routines do not maintain their own stack.
 *
 * @param xHandle The handle of the co-routine to delay.  This is the xHandle
 * parameter of the co-routine function.
 *
 * @param xTickToDelay The number of ticks that the co-routine should delay
 * for.  The actual amount of time this equates to is defined by
 * configTICK_RATE_HZ (set in FreeRTOSConfig.h).  The constant portTICK_PERIOD_MS
 * can be used to convert ticks to milliseconds.
 *
 * Example usage:
 * <pre>
 * // Co-routine to be created.
 * void vACoRoutine( CoRoutineHandle_t xHandle, UBaseType_t uxIndex )
 * {
 * // Variables in co-routines must be declared static if they must maintain value across a blocking call.
 * // This may not be necessary for const variables.
 * // We are to delay for 200ms.
 * static const xTickType xDelayTime = 200 / portTICK_PERIOD_MS;
 *
 *   // Must start every co-routine with a call to crSTART();
 *   crSTART( xHandle );
 *
 *   for( ;; )
 *   {
 *      // Delay for 200ms.
 *      crDELAY( xHandle, xDelayTime );
 *
 *      // Do something here.
 *   }
 *
 *   // Must end every co-routine with a call to crEND();
 *   crEND();
 * }</pre>
 * \defgroup crDELAY crDELAY
 * \ingroup Tasks
 */
    #define crDELAY( xHandle, xTicksToDelay )                  \
    if( ( xTicksToDelay ) > 0 )                                \
    {                                                          \
        vCoRoutineAddToDelayedList( ( xTicksToDelay ), NULL ); \
    }                                                          \
    crSET_STATE0( ( xHandle ) );

/**
 * <pre>
 * crQUEUE_SEND(
 *                CoRoutineHandle_t xHandle,
 *                QueueHandle_t pxQueue,
 *                void *pvItemToQueue,
 *                TickType_t xTicksToWait,
 *                BaseType_t *pxResult
 *           )</pre>
 *
 * The macro's crQUEUE_SEND() and crQUEUE_RECEIVE() are the co-routine
 * equivalent to the xQueueSend() and xQueueReceive() functions used by tasks.
 *
 * crQUEUE_SEND and crQUEUE_RECEIVE can only be used from a co-routine whereas
 * xQueueSend() and xQueueReceive() can only be used from tasks.
 *
 * crQUEUE_SEND can only be called from the co-routine function itself - not
 * from within a function called by the co-routine function.  This is because
 * co-routines do not maintain their own stack.
 *
 * See the co-routine section of the WEB documentation for information on
 * passing data between tasks and co-routines and between ISR's and
 * co-routines.
 *
 * @param xHandle The handle of the calling co-routine.  This is the xHandle
 * parameter of the co-routine function.
 *
 * @param pxQueue The handle of the queue on which the data will be posted.
 * The handle is obtained as the return value when the queue is created using
 * the xQueueCreate() API function.
 *
 * @param pvItemToQueue A pointer to the data being posted onto the queue.
 * The number of bytes of each queued item is specified when the queue is
 * created.  This number of bytes is copied from pvItemToQueue into the queue
 * itself.
 *
 * @param xTickToDelay The number of ticks that the co-routine should block
 * to wait for space to become available on the queue, should space not be
 * available immediately. The actual amount of time this equates to is defined
 * by configTICK_RATE_HZ (set in FreeRTOSConfig.h).  The constant
 * portTICK_PERIOD_MS can be used to convert ticks to milliseconds (see example
 * below).
 *
 * @param pxResult The variable pointed to by pxResult will be set to pdPASS if
 * data was successfully posted onto the queue, otherwise it will be set to an
 * error defined within ProjDefs.h.
 *
 * Example usage:
 * <pre>
 * // Co-routine function that blocks for a fixed period then posts a number onto
 * // a queue.
 * static void prvCoRoutineFlashTask( CoRoutineHandle_t xHandle, UBaseType_t uxIndex )
 * {
 * // Variables in co-routines must be declared static if they must maintain value across a blocking call.
 * static BaseType_t xNumberToPost = 0;
 * static BaseType_t xResult;
 *
 *  // Co-routines must begin with a call to crSTART().
 *  crSTART( xHandle );
 *
 *  for( ;; )
 *  {
 *      // This assumes the queue has already been created.
 *      crQUEUE_SEND( xHandle, xCoRoutineQueue, &xNumberToPost, NO_DELAY, &xResult );
 *
 *      if( xResult != pdPASS )
 *      {
 *          // The message was not posted!
 *      }
 *
 *      // Increment the number to be posted onto the queue.
 *      xNumberToPost++;
 *
 *      // Delay for 100 ticks.
 *      crDELAY( xHandle, 100 );
 *  }
 *
 *  // Co-routines must end with a call to crEND().
 *  crEND();
 * }</pre>
 * \defgroup crQUEUE_SEND crQUEUE_SEND
 * \ingroup Tasks
 */
    #define crQUEUE_SEND( xHandle, pxQueue, pvItemToQueue, xTicksToWait, pxResult )       \
    {                                                                                     \
        *( pxResult ) = xQueueCRSend( ( pxQueue ), ( pvItemToQueue ), ( xTicksToWait ) ); \
        if( *( pxResult ) == errQUEUE_BLOCKED )                                           \
        {                                                                                 \
            crSET_STATE0( ( xHandle ) );                                                  \
            *pxResult = xQueueCRSend( ( pxQueue ), ( pvItemToQueue ), 0 );                \
        }                                                                                 \
        if( *pxResult == errQUEUE_YIELD )                                                 \
        {                                                                                 \
            crSET_STATE1( ( xHandle ) );                                                  \
            *pxResult = pdPASS;                                                           \
        }                                                                                 \
    }

/**
 * croutine. h
 * <pre>
 * crQUEUE_RECEIVE(
 *                   CoRoutineHandle_t xHandle,
 *                   QueueHandle_t pxQueue,
 *                   void *pvBuffer,
 *                   TickType_t xTicksToWait,
 *                   BaseType_t *pxResult
 *               )</pre>
 *
 * The macro's crQUEUE_SEND() and crQUEUE_RECEIVE() are the co-routine
 * equivalent to the xQueueSend() and xQueueReceive() functions used by tasks.
 *
 * crQUEUE_SEND and crQUEUE_RECEIVE can only be used from a co-routine whereas
 * xQueueSend() and xQueueReceive() can only be used from tasks.
 *
 * crQUEUE_RECEIVE can only be called from the co-routine function itself - not
 * from within a function called by the co-routine function.  This is because
 * co-routines do not maintain their own stack.
 *
 * See the co-routine section of the WEB documentation for information on
 * passing data between tasks and co-routines and between ISR's and
 * co-routines.
 *
 * @param xHandle The handle of the calling co-routine.  This is the xHandle
 * parameter of the co-routine function.
 *
 * @param pxQueue The handle of the queue from which the data will be received.
 * The handle is obtained as the return value when the queue is created using
 * the xQueueCreate() API function.
 *
 * @param pvBuffer The buffer into which the received item is to be copied.
 * The number of bytes of each queued item is specified when the queue is
 * created.  This number of bytes is copied into pvBuffer.
 *
 * @param xTickToDelay The number of ticks that the co-routine should block
 * to wait for data to become available from the queue, should data not be
 * available immediately. The actual amount of time this equates to is defined
 * by configTICK_RATE_HZ (set in FreeRTOSConfig.h).  The constant
 * portTICK_PERIOD_MS can be used to convert ticks to milliseconds (see the
 * crQUEUE_SEND example).
 *
 * @param pxResult The variable pointed to by pxResult will be set to pdPASS if
 * data was successfully retrieved from the queue, otherwise it will be set to
 * an error code as defined within ProjDefs.h.
 *
 * Example usage:
 * <pre>
 * // A co-routine receives the number of an LED to flash from a queue.  It
 * // blocks on the queue until the number is received.
 * static void prvCoRoutineFlashWorkTask( CoRoutineHandle_t xHandle, UBaseType_t uxIndex )
 * {
 * // Variables in co-routines must be declared static if they must maintain value across a blocking call.
 * static BaseType_t xResult;
 * static UBaseType_t uxLEDToFlash;
 *
 *  // All co-routines must start with a call to crSTART().
 *  crSTART( xHandle );
 *
 *  for( ;; )
 *  {
 *      // Wait for data to become available on the queue.
 *      crQUEUE_RECEIVE( xHandle, xCoRoutineQueue, &uxLEDToFlash, portMAX_DELAY, &xResult );
 *
 *      if( xResult == pdPASS )
 *      {
 *          // We received the LED to flash - flash it!
 *          vParTestToggleLED( uxLEDToFlash );
 *      }
 *  }
 *
 *  crEND();
 * }</pre>
 * \defgroup crQUEUE_RECEIVE crQUEUE_RECEIVE
 * \ingroup Tasks
 */
    #define crQUEUE_RECEIVE( xHandle, pxQueue, pvBuffer, xTicksToWait, pxResult )       \
    {                                                                                   \
        *( pxResult ) = xQueueCRReceive( ( pxQueue ), ( pvBuffer ), ( xTicksToWait ) ); \
        if( *( pxResult ) == errQUEUE_BLOCKED )                                         \
        {                                                                               \
            crSET_STATE0( ( xHandle ) );                                                \
            *( pxResult ) = xQueueCRReceive( ( pxQueue ), ( pvBuffer ), 0 );            \
        }                                                                               \
        if( *( pxResult ) == errQUEUE_YIELD )                                           \
        {                                                                               \
            crSET_STATE1( ( xHandle ) );                                                \
            *( pxResult ) = pdPASS;                                                     \
        }                                                                               \
    }

/**
 * croutine. h
 * <pre>
 * crQUEUE_SEND_FROM_ISR(
 *                          QueueHandle_t pxQueue,
 *                          void *pvItemToQueue,
 *                          BaseType_t xCoRoutinePreviouslyWoken
 *                     )</pre>
 *
 * The macro's crQUEUE_SEND_FROM_ISR() and crQUEUE_RECEIVE_FROM_ISR() are the
 * co-routine equivalent to the xQueueSendFromISR() and xQueueReceiveFromISR()
 * functions used by tasks.
 *
 * crQUEUE_SEND_FROM_ISR() and crQUEUE_RECEIVE_FROM_ISR() can only be used to
 * pass data between a co-routine and and ISR, whereas xQueueSendFromISR() and
 * xQueueReceiveFromISR() can only be used to pass data between a task and and
 * ISR.
 *
 * crQUEUE_SEND_FROM_ISR can only be called from an ISR to send data to a queue
 * that is being used from within a co-routine.
 *
 * See the co-routine section of the WEB documentation for information on
 * passing data between tasks and co-routines and between ISR's and
 * co-routines.
 *
 * @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 xCoRoutinePreviouslyWoken This is included so an ISR can post onto
 * the same queue multiple times from a single interrupt.  The first call
 * should always pass in pdFALSE.  Subsequent calls should pass in
 * the value returned from the previous call.
 *
 * @return pdTRUE if a co-routine was woken by posting onto the queue.  This is
 * used by the ISR to determine if a context switch may be required following
 * the ISR.
 *
 * Example usage:
 * <pre>
 * // A co-routine that blocks on a queue waiting for characters to be received.
 * static void vReceivingCoRoutine( CoRoutineHandle_t xHandle, UBaseType_t uxIndex )
 * {
 * char cRxedChar;
 * BaseType_t xResult;
 *
 *   // All co-routines must start with a call to crSTART().
 *   crSTART( xHandle );
 *
 *   for( ;; )
 *   {
 *       // Wait for data to become available on the queue.  This assumes the
 *       // queue xCommsRxQueue has already been created!
 *       crQUEUE_RECEIVE( xHandle, xCommsRxQueue, &uxLEDToFlash, portMAX_DELAY, &xResult );
 *
 *       // Was a character received?
 *       if( xResult == pdPASS )
 *       {
 *           // Process the character here.
 *       }
 *   }
 *
 *   // All co-routines must end with a call to crEND().
 *   crEND();
 * }
 *
 * // An ISR that uses a queue to send characters received on a serial port to
 * // a co-routine.
 * void vUART_ISR( void )
 * {
 * char cRxedChar;
 * BaseType_t xCRWokenByPost = pdFALSE;
 *
 *   // We loop around reading characters until there are none left in the UART.
 *   while( UART_RX_REG_NOT_EMPTY() )
 *   {
 *       // Obtain the character from the UART.
 *       cRxedChar = UART_RX_REG;
 *
 *       // Post the character onto a queue.  xCRWokenByPost will be pdFALSE
 *       // the first time around the loop.  If the post causes a co-routine
 *       // to be woken (unblocked) then xCRWokenByPost will be set to pdTRUE.
 *       // In this manner we can ensure that if more than one co-routine is
 *       // blocked on the queue only one is woken by this ISR no matter how
 *       // many characters are posted to the queue.
 *       xCRWokenByPost = crQUEUE_SEND_FROM_ISR( xCommsRxQueue, &cRxedChar, xCRWokenByPost );
 *   }
 * }</pre>
 * \defgroup crQUEUE_SEND_FROM_ISR crQUEUE_SEND_FROM_ISR
 * \ingroup Tasks
 */
    #define crQUEUE_SEND_FROM_ISR( pxQueue, pvItemToQueue, xCoRoutinePreviouslyWoken )    xQueueCRSendFromISR( ( pxQueue ), ( pvItemToQueue ), ( xCoRoutinePreviouslyWoken ) )


/**
 * croutine. h
 * <pre>
 * crQUEUE_SEND_FROM_ISR(
 *                          QueueHandle_t pxQueue,
 *                          void *pvBuffer,
 *                          BaseType_t * pxCoRoutineWoken
 *                     )</pre>
 *
 * The macro's crQUEUE_SEND_FROM_ISR() and crQUEUE_RECEIVE_FROM_ISR() are the
 * co-routine equivalent to the xQueueSendFromISR() and xQueueReceiveFromISR()
 * functions used by tasks.
 *
 * crQUEUE_SEND_FROM_ISR() and crQUEUE_RECEIVE_FROM_ISR() can only be used to
 * pass data between a co-routine and and ISR, whereas xQueueSendFromISR() and
 * xQueueReceiveFromISR() can only be used to pass data between a task and and
 * ISR.
 *
 * crQUEUE_RECEIVE_FROM_ISR can only be called from an ISR to receive data
 * from a queue that is being used from within a co-routine (a co-routine
 * posted to the queue).
 *
 * See the co-routine section of the WEB documentation for information on
 * passing data between tasks and co-routines and between ISR's and
 * co-routines.
 *
 * @param xQueue The handle to the queue on which the item is to be posted.
 *
 * @param pvBuffer A pointer to a buffer into which the received item will be
 * placed.  The size of the items the queue will hold was defined when the
 * queue was created, so this many bytes will be copied from the queue into
 * pvBuffer.
 *
 * @param pxCoRoutineWoken A co-routine may be blocked waiting for space to become
 * available on the queue.  If crQUEUE_RECEIVE_FROM_ISR causes such a
 * co-routine to unblock *pxCoRoutineWoken will get set to pdTRUE, otherwise
 * *pxCoRoutineWoken will remain unchanged.
 *
 * @return pdTRUE an item was successfully received from the queue, otherwise
 * pdFALSE.
 *
 * Example usage:
 * <pre>
 * // A co-routine that posts a character to a queue then blocks for a fixed
 * // period.  The character is incremented each time.
 * static void vSendingCoRoutine( CoRoutineHandle_t xHandle, UBaseType_t uxIndex )
 * {
 * // cChar holds its value while this co-routine is blocked and must therefore
 * // be declared static.
 * static char cCharToTx = 'a';
 * BaseType_t xResult;
 *
 *   // All co-routines must start with a call to crSTART().
 *   crSTART( xHandle );
 *
 *   for( ;; )
 *   {
 *       // Send the next character to the queue.
 *       crQUEUE_SEND( xHandle, xCoRoutineQueue, &cCharToTx, NO_DELAY, &xResult );
 *
 *       if( xResult == pdPASS )
 *       {
 *           // The character was successfully posted to the queue.
 *       }
 *       else
 *       {
 *          // Could not post the character to the queue.
 *       }
 *
 *       // Enable the UART Tx interrupt to cause an interrupt in this
 *       // hypothetical UART.  The interrupt will obtain the character
 *       // from the queue and send it.
 *       ENABLE_RX_INTERRUPT();
 *
 *       // Increment to the next character then block for a fixed period.
 *       // cCharToTx will maintain its value across the delay as it is
 *       // declared static.
 *       cCharToTx++;
 *       if( cCharToTx > 'x' )
 *       {
 *          cCharToTx = 'a';
 *       }
 *       crDELAY( 100 );
 *   }
 *
 *   // All co-routines must end with a call to crEND().
 *   crEND();
 * }
 *
 * // An ISR that uses a queue to receive characters to send on a UART.
 * void vUART_ISR( void )
 * {
 * char cCharToTx;
 * BaseType_t xCRWokenByPost = pdFALSE;
 *
 *   while( UART_TX_REG_EMPTY() )
 *   {
 *       // Are there any characters in the queue waiting to be sent?
 *       // xCRWokenByPost will automatically be set to pdTRUE if a co-routine
 *       // is woken by the post - ensuring that only a single co-routine is
 *       // woken no matter how many times we go around this loop.
 *       if( crQUEUE_RECEIVE_FROM_ISR( pxQueue, &cCharToTx, &xCRWokenByPost ) )
 *       {
 *           SEND_CHARACTER( cCharToTx );
 *       }
 *   }
 * }</pre>
 * \defgroup crQUEUE_RECEIVE_FROM_ISR crQUEUE_RECEIVE_FROM_ISR
 * \ingroup Tasks
 */
    #define crQUEUE_RECEIVE_FROM_ISR( pxQueue, pvBuffer, pxCoRoutineWoken )    xQueueCRReceiveFromISR( ( pxQueue ), ( pvBuffer ), ( pxCoRoutineWoken ) )

/*
 * This function is intended for internal use by the co-routine macros only.
 * The macro nature of the co-routine implementation requires that the
 * prototype appears here.  The function should not be used by application
 * writers.
 *
 * Removes the current co-routine from its ready list and places it in the
 * appropriate delayed list.
 */
    void vCoRoutineAddToDelayedList( TickType_t xTicksToDelay,
                                     List_t * pxEventList );

/*
 * This function is intended for internal use by the queue implementation only.
 * The function should not be used by application writers.
 *
 * Removes the highest priority co-routine from the event list and places it in
 * the pending ready list.
 */
    BaseType_t xCoRoutineRemoveFromEventList( const List_t * pxEventList );

    #ifdef __cplusplus
        }
    #endif

#endif /* CO_ROUTINE_H */