circuitpython/cc3200/FreeRTOS/Source/include/semphr.h

/*
    FreeRTOS V9.0.0 - Copyright (C) 2016 Real Time Engineers Ltd.
    All rights reserved

    VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.

    This file is part of the FreeRTOS distribution.

    FreeRTOS is free software; you can redistribute it and/or modify it under
    the terms of the GNU General Public License (version 2) as published by the
    Free Software Foundation >>>> AND MODIFIED BY <<<< the FreeRTOS exception.

    ***************************************************************************
    >>!   NOTE: The modification to the GPL is included to allow you to     !<<
    >>!   distribute a combined work that includes FreeRTOS without being   !<<
    >>!   obliged to provide the source code for proprietary components     !<<
    >>!   outside of the FreeRTOS kernel.                                   !<<
    ***************************************************************************

    FreeRTOS is distributed in the hope that it will be useful, but WITHOUT ANY
    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
    FOR A PARTICULAR PURPOSE.  Full license text is available on the following
    link: http://www.freertos.org/a00114.html

    ***************************************************************************
     *                                                                       *
     *    FreeRTOS provides completely free yet professionally developed,    *
     *    robust, strictly quality controlled, supported, and cross          *
     *    platform software that is more than just the market leader, it     *
     *    is the industry's de facto standard.                               *
     *                                                                       *
     *    Help yourself get started quickly while simultaneously helping     *
     *    to support the FreeRTOS project by purchasing a FreeRTOS           *
     *    tutorial book, reference manual, or both:                          *
     *    http://www.FreeRTOS.org/Documentation                              *
     *                                                                       *
    ***************************************************************************

    http://www.FreeRTOS.org/FAQHelp.html - Having a problem?  Start by reading
    the FAQ page "My application does not run, what could be wrong?".  Have you
    defined configASSERT()?

    http://www.FreeRTOS.org/support - In return for receiving this top quality
    embedded software for free we request you assist our global community by
    participating in the support forum.

    http://www.FreeRTOS.org/training - Investing in training allows your team to
    be as productive as possible as early as possible.  Now you can receive
    FreeRTOS training directly from Richard Barry, CEO of Real Time Engineers
    Ltd, and the world's leading authority on the world's leading RTOS.

    http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products,
    including FreeRTOS+Trace - an indispensable productivity tool, a DOS
    compatible FAT file system, and our tiny thread aware UDP/IP stack.

    http://www.FreeRTOS.org/labs - Where new FreeRTOS products go to incubate.
    Come and try FreeRTOS+TCP, our new open source TCP/IP stack for FreeRTOS.

    http://www.OpenRTOS.com - Real Time Engineers ltd. license FreeRTOS to High
    Integrity Systems ltd. to sell under the OpenRTOS brand.  Low cost OpenRTOS
    licenses offer ticketed support, indemnification and commercial middleware.

    http://www.SafeRTOS.com - High Integrity Systems also provide a safety
    engineered and independently SIL3 certified version for use in safety and
    mission critical applications that require provable dependability.

    1 tab == 4 spaces!
*/

#ifndef SEMAPHORE_H
#define SEMAPHORE_H

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

#include "queue.h"

typedef QueueHandle_t SemaphoreHandle_t;

#define semBINARY_SEMAPHORE_QUEUE_LENGTH	( ( uint8_t ) 1U )
#define semSEMAPHORE_QUEUE_ITEM_LENGTH		( ( uint8_t ) 0U )
#define semGIVE_BLOCK_TIME					( ( TickType_t ) 0U )


/**
 * semphr. h
 * <pre>vSemaphoreCreateBinary( SemaphoreHandle_t xSemaphore )</pre>
 *
 * In many usage scenarios it is faster and more memory efficient to use a
 * direct to task notification in place of a binary semaphore!
 * http://www.freertos.org/RTOS-task-notifications.html
 *
 * This old vSemaphoreCreateBinary() macro is now deprecated in favour of the
 * xSemaphoreCreateBinary() function.  Note that binary semaphores created using
 * the vSemaphoreCreateBinary() macro are created in a state such that the
 * first call to 'take' the semaphore would pass, whereas binary semaphores
 * created using xSemaphoreCreateBinary() are created in a state such that the
 * the semaphore must first be 'given' before it can be 'taken'.
 *
 * <i>Macro</i> that implements a semaphore by using the existing queue mechanism.
 * The queue length is 1 as this is a binary semaphore.  The data size is 0
 * as we don't want to actually store any data - we just want to know if the
 * queue is empty or full.
 *
 * This type of semaphore can be used for pure synchronisation between tasks or
 * between an interrupt and a task.  The semaphore need not be given back once
 * obtained, so one task/interrupt can continuously 'give' the semaphore while
 * another continuously 'takes' the semaphore.  For this reason this type of
 * semaphore does not use a priority inheritance mechanism.  For an alternative
 * that does use priority inheritance see xSemaphoreCreateMutex().
 *
 * @param xSemaphore Handle to the created semaphore.  Should be of type SemaphoreHandle_t.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore = NULL;

 void vATask( void * pvParameters )
 {
    // Semaphore cannot be used before a call to vSemaphoreCreateBinary ().
    // This is a macro so pass the variable in directly.
    vSemaphoreCreateBinary( xSemaphore );

    if( xSemaphore != NULL )
    {
        // The semaphore was created successfully.
        // The semaphore can now be used.
    }
 }
 </pre>
 * \defgroup vSemaphoreCreateBinary vSemaphoreCreateBinary
 * \ingroup Semaphores
 */
#if( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
	#define vSemaphoreCreateBinary( xSemaphore )																							\
		{																																	\
			( xSemaphore ) = xQueueGenericCreate( ( UBaseType_t ) 1, semSEMAPHORE_QUEUE_ITEM_LENGTH, queueQUEUE_TYPE_BINARY_SEMAPHORE );	\
			if( ( xSemaphore ) != NULL )																									\
			{																																\
				( void ) xSemaphoreGive( ( xSemaphore ) );																					\
			}																																\
		}
#endif

/**
 * semphr. h
 * <pre>SemaphoreHandle_t xSemaphoreCreateBinary( void )</pre>
 *
 * Creates a new binary semaphore instance, and returns a handle by which the
 * new semaphore can be referenced.
 *
 * In many usage scenarios it is faster and more memory efficient to use a
 * direct to task notification in place of a binary semaphore!
 * http://www.freertos.org/RTOS-task-notifications.html
 *
 * Internally, within the FreeRTOS implementation, binary semaphores use a block
 * of memory, in which the semaphore structure is stored.  If a binary semaphore
 * is created using xSemaphoreCreateBinary() then the required memory is
 * automatically dynamically allocated inside the xSemaphoreCreateBinary()
 * function.  (see http://www.freertos.org/a00111.html).  If a binary semaphore
 * is created using xSemaphoreCreateBinaryStatic() then the application writer
 * must provide the memory.  xSemaphoreCreateBinaryStatic() therefore allows a
 * binary semaphore to be created without using any dynamic memory allocation.
 *
 * The old vSemaphoreCreateBinary() macro is now deprecated in favour of this
 * xSemaphoreCreateBinary() function.  Note that binary semaphores created using
 * the vSemaphoreCreateBinary() macro are created in a state such that the
 * first call to 'take' the semaphore would pass, whereas binary semaphores
 * created using xSemaphoreCreateBinary() are created in a state such that the
 * the semaphore must first be 'given' before it can be 'taken'.
 *
 * This type of semaphore can be used for pure synchronisation between tasks or
 * between an interrupt and a task.  The semaphore need not be given back once
 * obtained, so one task/interrupt can continuously 'give' the semaphore while
 * another continuously 'takes' the semaphore.  For this reason this type of
 * semaphore does not use a priority inheritance mechanism.  For an alternative
 * that does use priority inheritance see xSemaphoreCreateMutex().
 *
 * @return Handle to the created semaphore, or NULL if the memory required to
 * hold the semaphore's data structures could not be allocated.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore = NULL;

 void vATask( void * pvParameters )
 {
    // Semaphore cannot be used before a call to xSemaphoreCreateBinary().
    // This is a macro so pass the variable in directly.
    xSemaphore = xSemaphoreCreateBinary();

    if( xSemaphore != NULL )
    {
        // The semaphore was created successfully.
        // The semaphore can now be used.
    }
 }
 </pre>
 * \defgroup xSemaphoreCreateBinary xSemaphoreCreateBinary
 * \ingroup Semaphores
 */
#if( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
	#define xSemaphoreCreateBinary() xQueueGenericCreate( ( UBaseType_t ) 1, semSEMAPHORE_QUEUE_ITEM_LENGTH, queueQUEUE_TYPE_BINARY_SEMAPHORE )
#endif

/**
 * semphr. h
 * <pre>SemaphoreHandle_t xSemaphoreCreateBinaryStatic( StaticSemaphore_t *pxSemaphoreBuffer )</pre>
 *
 * Creates a new binary semaphore instance, and returns a handle by which the
 * new semaphore can be referenced.
 *
 * NOTE: In many usage scenarios it is faster and more memory efficient to use a
 * direct to task notification in place of a binary semaphore!
 * http://www.freertos.org/RTOS-task-notifications.html
 *
 * Internally, within the FreeRTOS implementation, binary semaphores use a block
 * of memory, in which the semaphore structure is stored.  If a binary semaphore
 * is created using xSemaphoreCreateBinary() then the required memory is
 * automatically dynamically allocated inside the xSemaphoreCreateBinary()
 * function.  (see http://www.freertos.org/a00111.html).  If a binary semaphore
 * is created using xSemaphoreCreateBinaryStatic() then the application writer
 * must provide the memory.  xSemaphoreCreateBinaryStatic() therefore allows a
 * binary semaphore to be created without using any dynamic memory allocation.
 *
 * This type of semaphore can be used for pure synchronisation between tasks or
 * between an interrupt and a task.  The semaphore need not be given back once
 * obtained, so one task/interrupt can continuously 'give' the semaphore while
 * another continuously 'takes' the semaphore.  For this reason this type of
 * semaphore does not use a priority inheritance mechanism.  For an alternative
 * that does use priority inheritance see xSemaphoreCreateMutex().
 *
 * @param pxSemaphoreBuffer Must point to a variable of type StaticSemaphore_t,
 * which will then be used to hold the semaphore's data structure, removing the
 * need for the memory to be allocated dynamically.
 *
 * @return If the semaphore is created then a handle to the created semaphore is
 * returned.  If pxSemaphoreBuffer is NULL then NULL is returned.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore = NULL;
 StaticSemaphore_t xSemaphoreBuffer;

 void vATask( void * pvParameters )
 {
    // Semaphore cannot be used before a call to xSemaphoreCreateBinary().
    // The semaphore's data structures will be placed in the xSemaphoreBuffer
    // variable, the address of which is passed into the function.  The
    // function's parameter is not NULL, so the function will not attempt any
    // dynamic memory allocation, and therefore the function will not return
    // return NULL.
    xSemaphore = xSemaphoreCreateBinary( &xSemaphoreBuffer );

    // Rest of task code goes here.
 }
 </pre>
 * \defgroup xSemaphoreCreateBinaryStatic xSemaphoreCreateBinaryStatic
 * \ingroup Semaphores
 */
#if( configSUPPORT_STATIC_ALLOCATION == 1 )
	#define xSemaphoreCreateBinaryStatic( pxStaticSemaphore ) xQueueGenericCreateStatic( ( UBaseType_t ) 1, semSEMAPHORE_QUEUE_ITEM_LENGTH, NULL, pxStaticSemaphore, queueQUEUE_TYPE_BINARY_SEMAPHORE )
#endif /* configSUPPORT_STATIC_ALLOCATION */

/**
 * semphr. h
 * <pre>xSemaphoreTake(
 *                   SemaphoreHandle_t xSemaphore,
 *                   TickType_t xBlockTime
 *               )</pre>
 *
 * <i>Macro</i> to obtain a semaphore.  The semaphore must have previously been
 * created with a call to xSemaphoreCreateBinary(), xSemaphoreCreateMutex() or
 * xSemaphoreCreateCounting().
 *
 * @param xSemaphore A handle to the semaphore being taken - obtained when
 * the semaphore was created.
 *
 * @param xBlockTime The time in ticks to wait for the semaphore to become
 * available.  The macro portTICK_PERIOD_MS can be used to convert this to a
 * real time.  A block time of zero can be used to poll the semaphore.  A block
 * time of portMAX_DELAY can be used to block indefinitely (provided
 * INCLUDE_vTaskSuspend is set to 1 in FreeRTOSConfig.h).
 *
 * @return pdTRUE if the semaphore was obtained.  pdFALSE
 * if xBlockTime expired without the semaphore becoming available.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore = NULL;

 // A task that creates a semaphore.
 void vATask( void * pvParameters )
 {
    // Create the semaphore to guard a shared resource.
    xSemaphore = xSemaphoreCreateBinary();
 }

 // A task that uses the semaphore.
 void vAnotherTask( void * pvParameters )
 {
    // ... Do other things.

    if( xSemaphore != NULL )
    {
        // See if we can obtain the semaphore.  If the semaphore is not available
        // wait 10 ticks to see if it becomes free.
        if( xSemaphoreTake( xSemaphore, ( TickType_t ) 10 ) == pdTRUE )
        {
            // We were able to obtain the semaphore and can now access the
            // shared resource.

            // ...

            // We have finished accessing the shared resource.  Release the
            // semaphore.
            xSemaphoreGive( xSemaphore );
        }
        else
        {
            // We could not obtain the semaphore and can therefore not access
            // the shared resource safely.
        }
    }
 }
 </pre>
 * \defgroup xSemaphoreTake xSemaphoreTake
 * \ingroup Semaphores
 */
#define xSemaphoreTake( xSemaphore, xBlockTime )		xQueueGenericReceive( ( QueueHandle_t ) ( xSemaphore ), NULL, ( xBlockTime ), pdFALSE )

/**
 * semphr. h
 * xSemaphoreTakeRecursive(
 *                          SemaphoreHandle_t xMutex,
 *                          TickType_t xBlockTime
 *                        )
 *
 * <i>Macro</i> to recursively obtain, or 'take', a mutex type semaphore.
 * The mutex must have previously been created using a call to
 * xSemaphoreCreateRecursiveMutex();
 *
 * configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this
 * macro to be available.
 *
 * This macro must not be used on mutexes created using xSemaphoreCreateMutex().
 *
 * A mutex used recursively can be 'taken' repeatedly by the owner. The mutex
 * doesn't become available again until the owner has called
 * xSemaphoreGiveRecursive() for each successful 'take' request.  For example,
 * if a task successfully 'takes' the same mutex 5 times then the mutex will
 * not be available to any other task until it has also  'given' the mutex back
 * exactly five times.
 *
 * @param xMutex A handle to the mutex being obtained.  This is the
 * handle returned by xSemaphoreCreateRecursiveMutex();
 *
 * @param xBlockTime The time in ticks to wait for the semaphore to become
 * available.  The macro portTICK_PERIOD_MS can be used to convert this to a
 * real time.  A block time of zero can be used to poll the semaphore.  If
 * the task already owns the semaphore then xSemaphoreTakeRecursive() will
 * return immediately no matter what the value of xBlockTime.
 *
 * @return pdTRUE if the semaphore was obtained.  pdFALSE if xBlockTime
 * expired without the semaphore becoming available.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xMutex = NULL;

 // A task that creates a mutex.
 void vATask( void * pvParameters )
 {
    // Create the mutex to guard a shared resource.
    xMutex = xSemaphoreCreateRecursiveMutex();
 }

 // A task that uses the mutex.
 void vAnotherTask( void * pvParameters )
 {
    // ... Do other things.

    if( xMutex != NULL )
    {
        // See if we can obtain the mutex.  If the mutex is not available
        // wait 10 ticks to see if it becomes free.
        if( xSemaphoreTakeRecursive( xSemaphore, ( TickType_t ) 10 ) == pdTRUE )
        {
            // We were able to obtain the mutex and can now access the
            // shared resource.

            // ...
            // For some reason due to the nature of the code further calls to
			// xSemaphoreTakeRecursive() are made on the same mutex.  In real
			// code these would not be just sequential calls as this would make
			// no sense.  Instead the calls are likely to be buried inside
			// a more complex call structure.
            xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 );
            xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 );

            // The mutex has now been 'taken' three times, so will not be
			// available to another task until it has also been given back
			// three times.  Again it is unlikely that real code would have
			// these calls sequentially, but instead buried in a more complex
			// call structure.  This is just for illustrative purposes.
            xSemaphoreGiveRecursive( xMutex );
			xSemaphoreGiveRecursive( xMutex );
			xSemaphoreGiveRecursive( xMutex );

			// Now the mutex can be taken by other tasks.
        }
        else
        {
            // We could not obtain the mutex and can therefore not access
            // the shared resource safely.
        }
    }
 }
 </pre>
 * \defgroup xSemaphoreTakeRecursive xSemaphoreTakeRecursive
 * \ingroup Semaphores
 */
#if( configUSE_RECURSIVE_MUTEXES == 1 )
	#define xSemaphoreTakeRecursive( xMutex, xBlockTime )	xQueueTakeMutexRecursive( ( xMutex ), ( xBlockTime ) )
#endif

/**
 * semphr. h
 * <pre>xSemaphoreGive( SemaphoreHandle_t xSemaphore )</pre>
 *
 * <i>Macro</i> to release a semaphore.  The semaphore must have previously been
 * created with a call to xSemaphoreCreateBinary(), xSemaphoreCreateMutex() or
 * xSemaphoreCreateCounting(). and obtained using sSemaphoreTake().
 *
 * This macro must not be used from an ISR.  See xSemaphoreGiveFromISR () for
 * an alternative which can be used from an ISR.
 *
 * This macro must also not be used on semaphores created using
 * xSemaphoreCreateRecursiveMutex().
 *
 * @param xSemaphore A handle to the semaphore being released.  This is the
 * handle returned when the semaphore was created.
 *
 * @return pdTRUE if the semaphore was released.  pdFALSE if an error occurred.
 * Semaphores are implemented using queues.  An error can occur if there is
 * no space on the queue to post a message - indicating that the
 * semaphore was not first obtained correctly.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore = NULL;

 void vATask( void * pvParameters )
 {
    // Create the semaphore to guard a shared resource.
    xSemaphore = vSemaphoreCreateBinary();

    if( xSemaphore != NULL )
    {
        if( xSemaphoreGive( xSemaphore ) != pdTRUE )
        {
            // We would expect this call to fail because we cannot give
            // a semaphore without first "taking" it!
        }

        // Obtain the semaphore - don't block if the semaphore is not
        // immediately available.
        if( xSemaphoreTake( xSemaphore, ( TickType_t ) 0 ) )
        {
            // We now have the semaphore and can access the shared resource.

            // ...

            // We have finished accessing the shared resource so can free the
            // semaphore.
            if( xSemaphoreGive( xSemaphore ) != pdTRUE )
            {
                // We would not expect this call to fail because we must have
                // obtained the semaphore to get here.
            }
        }
    }
 }
 </pre>
 * \defgroup xSemaphoreGive xSemaphoreGive
 * \ingroup Semaphores
 */
#define xSemaphoreGive( xSemaphore )		xQueueGenericSend( ( QueueHandle_t ) ( xSemaphore ), NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK )

/**
 * semphr. h
 * <pre>xSemaphoreGiveRecursive( SemaphoreHandle_t xMutex )</pre>
 *
 * <i>Macro</i> to recursively release, or 'give', a mutex type semaphore.
 * The mutex must have previously been created using a call to
 * xSemaphoreCreateRecursiveMutex();
 *
 * configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this
 * macro to be available.
 *
 * This macro must not be used on mutexes created using xSemaphoreCreateMutex().
 *
 * A mutex used recursively can be 'taken' repeatedly by the owner. The mutex
 * doesn't become available again until the owner has called
 * xSemaphoreGiveRecursive() for each successful 'take' request.  For example,
 * if a task successfully 'takes' the same mutex 5 times then the mutex will
 * not be available to any other task until it has also  'given' the mutex back
 * exactly five times.
 *
 * @param xMutex A handle to the mutex being released, or 'given'.  This is the
 * handle returned by xSemaphoreCreateMutex();
 *
 * @return pdTRUE if the semaphore was given.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xMutex = NULL;

 // A task that creates a mutex.
 void vATask( void * pvParameters )
 {
    // Create the mutex to guard a shared resource.
    xMutex = xSemaphoreCreateRecursiveMutex();
 }

 // A task that uses the mutex.
 void vAnotherTask( void * pvParameters )
 {
    // ... Do other things.

    if( xMutex != NULL )
    {
        // See if we can obtain the mutex.  If the mutex is not available
        // wait 10 ticks to see if it becomes free.
        if( xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 ) == pdTRUE )
        {
            // We were able to obtain the mutex and can now access the
            // shared resource.

            // ...
            // For some reason due to the nature of the code further calls to
			// xSemaphoreTakeRecursive() are made on the same mutex.  In real
			// code these would not be just sequential calls as this would make
			// no sense.  Instead the calls are likely to be buried inside
			// a more complex call structure.
            xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 );
            xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 );

            // The mutex has now been 'taken' three times, so will not be
			// available to another task until it has also been given back
			// three times.  Again it is unlikely that real code would have
			// these calls sequentially, it would be more likely that the calls
			// to xSemaphoreGiveRecursive() would be called as a call stack
			// unwound.  This is just for demonstrative purposes.
            xSemaphoreGiveRecursive( xMutex );
			xSemaphoreGiveRecursive( xMutex );
			xSemaphoreGiveRecursive( xMutex );

			// Now the mutex can be taken by other tasks.
        }
        else
        {
            // We could not obtain the mutex and can therefore not access
            // the shared resource safely.
        }
    }
 }
 </pre>
 * \defgroup xSemaphoreGiveRecursive xSemaphoreGiveRecursive
 * \ingroup Semaphores
 */
#if( configUSE_RECURSIVE_MUTEXES == 1 )
	#define xSemaphoreGiveRecursive( xMutex )	xQueueGiveMutexRecursive( ( xMutex ) )
#endif

/**
 * semphr. h
 * <pre>
 xSemaphoreGiveFromISR(
                          SemaphoreHandle_t xSemaphore,
                          BaseType_t *pxHigherPriorityTaskWoken
                      )</pre>
 *
 * <i>Macro</i> to  release a semaphore.  The semaphore must have previously been
 * created with a call to xSemaphoreCreateBinary() or xSemaphoreCreateCounting().
 *
 * Mutex type semaphores (those created using a call to xSemaphoreCreateMutex())
 * must not be used with this macro.
 *
 * This macro can be used from an ISR.
 *
 * @param xSemaphore A handle to the semaphore being released.  This is the
 * handle returned when the semaphore was created.
 *
 * @param pxHigherPriorityTaskWoken xSemaphoreGiveFromISR() will set
 * *pxHigherPriorityTaskWoken to pdTRUE if giving the semaphore caused a task
 * to unblock, and the unblocked task has a priority higher than the currently
 * running task.  If xSemaphoreGiveFromISR() sets this value to pdTRUE then
 * a context switch should be requested before the interrupt is exited.
 *
 * @return pdTRUE if the semaphore was successfully given, otherwise errQUEUE_FULL.
 *
 * Example usage:
 <pre>
 \#define LONG_TIME 0xffff
 \#define TICKS_TO_WAIT	10
 SemaphoreHandle_t xSemaphore = NULL;

 // Repetitive task.
 void vATask( void * pvParameters )
 {
    for( ;; )
    {
        // We want this task to run every 10 ticks of a timer.  The semaphore
        // was created before this task was started.

        // Block waiting for the semaphore to become available.
        if( xSemaphoreTake( xSemaphore, LONG_TIME ) == pdTRUE )
        {
            // It is time to execute.

            // ...

            // We have finished our task.  Return to the top of the loop where
            // we will block on the semaphore until it is time to execute
            // again.  Note when using the semaphore for synchronisation with an
			// ISR in this manner there is no need to 'give' the semaphore back.
        }
    }
 }

 // Timer ISR
 void vTimerISR( void * pvParameters )
 {
 static uint8_t ucLocalTickCount = 0;
 static BaseType_t xHigherPriorityTaskWoken;

    // A timer tick has occurred.

    // ... Do other time functions.

    // Is it time for vATask () to run?
	xHigherPriorityTaskWoken = pdFALSE;
    ucLocalTickCount++;
    if( ucLocalTickCount >= TICKS_TO_WAIT )
    {
        // Unblock the task by releasing the semaphore.
        xSemaphoreGiveFromISR( xSemaphore, &xHigherPriorityTaskWoken );

        // Reset the count so we release the semaphore again in 10 ticks time.
        ucLocalTickCount = 0;
    }

    if( xHigherPriorityTaskWoken != pdFALSE )
    {
        // We can force a context switch here.  Context switching from an
        // ISR uses port specific syntax.  Check the demo task for your port
        // to find the syntax required.
    }
 }
 </pre>
 * \defgroup xSemaphoreGiveFromISR xSemaphoreGiveFromISR
 * \ingroup Semaphores
 */
#define xSemaphoreGiveFromISR( xSemaphore, pxHigherPriorityTaskWoken )	xQueueGiveFromISR( ( QueueHandle_t ) ( xSemaphore ), ( pxHigherPriorityTaskWoken ) )

/**
 * semphr. h
 * <pre>
 xSemaphoreTakeFromISR(
                          SemaphoreHandle_t xSemaphore,
                          BaseType_t *pxHigherPriorityTaskWoken
                      )</pre>
 *
 * <i>Macro</i> to  take a semaphore from an ISR.  The semaphore must have
 * previously been created with a call to xSemaphoreCreateBinary() or
 * xSemaphoreCreateCounting().
 *
 * Mutex type semaphores (those created using a call to xSemaphoreCreateMutex())
 * must not be used with this macro.
 *
 * This macro can be used from an ISR, however taking a semaphore from an ISR
 * is not a common operation.  It is likely to only be useful when taking a
 * counting semaphore when an interrupt is obtaining an object from a resource
 * pool (when the semaphore count indicates the number of resources available).
 *
 * @param xSemaphore A handle to the semaphore being taken.  This is the
 * handle returned when the semaphore was created.
 *
 * @param pxHigherPriorityTaskWoken xSemaphoreTakeFromISR() will set
 * *pxHigherPriorityTaskWoken to pdTRUE if taking the semaphore caused a task
 * to unblock, and the unblocked task has a priority higher than the currently
 * running task.  If xSemaphoreTakeFromISR() sets this value to pdTRUE then
 * a context switch should be requested before the interrupt is exited.
 *
 * @return pdTRUE if the semaphore was successfully taken, otherwise
 * pdFALSE
 */
#define xSemaphoreTakeFromISR( xSemaphore, pxHigherPriorityTaskWoken )	xQueueReceiveFromISR( ( QueueHandle_t ) ( xSemaphore ), NULL, ( pxHigherPriorityTaskWoken ) )

/**
 * semphr. h
 * <pre>SemaphoreHandle_t xSemaphoreCreateMutex( void )</pre>
 *
 * Creates a new mutex type semaphore instance, and returns a handle by which
 * the new mutex can be referenced.
 *
 * Internally, within the FreeRTOS implementation, mutex semaphores use a block
 * of memory, in which the mutex structure is stored.  If a mutex is created
 * using xSemaphoreCreateMutex() then the required memory is automatically
 * dynamically allocated inside the xSemaphoreCreateMutex() function.  (see
 * http://www.freertos.org/a00111.html).  If a mutex is created using
 * xSemaphoreCreateMutexStatic() then the application writer must provided the
 * memory.  xSemaphoreCreateMutexStatic() therefore allows a mutex to be created
 * without using any dynamic memory allocation.
 *
 * Mutexes created using this function can be accessed using the xSemaphoreTake()
 * and xSemaphoreGive() macros.  The xSemaphoreTakeRecursive() and
 * xSemaphoreGiveRecursive() macros must not be used.
 *
 * This type of semaphore uses a priority inheritance mechanism so a task
 * 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the
 * semaphore it is no longer required.
 *
 * Mutex type semaphores cannot be used from within interrupt service routines.
 *
 * See xSemaphoreCreateBinary() for an alternative implementation that can be
 * used for pure synchronisation (where one task or interrupt always 'gives' the
 * semaphore and another always 'takes' the semaphore) and from within interrupt
 * service routines.
 *
 * @return If the mutex was successfully created then a handle to the created
 * semaphore is returned.  If there was not enough heap to allocate the mutex
 * data structures then NULL is returned.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore;

 void vATask( void * pvParameters )
 {
    // Semaphore cannot be used before a call to xSemaphoreCreateMutex().
    // This is a macro so pass the variable in directly.
    xSemaphore = xSemaphoreCreateMutex();

    if( xSemaphore != NULL )
    {
        // The semaphore was created successfully.
        // The semaphore can now be used.
    }
 }
 </pre>
 * \defgroup xSemaphoreCreateMutex xSemaphoreCreateMutex
 * \ingroup Semaphores
 */
#if( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
	#define xSemaphoreCreateMutex() xQueueCreateMutex( queueQUEUE_TYPE_MUTEX )
#endif

/**
 * semphr. h
 * <pre>SemaphoreHandle_t xSemaphoreCreateMutexStatic( StaticSemaphore_t *pxMutexBuffer )</pre>
 *
 * Creates a new mutex type semaphore instance, and returns a handle by which
 * the new mutex can be referenced.
 *
 * Internally, within the FreeRTOS implementation, mutex semaphores use a block
 * of memory, in which the mutex structure is stored.  If a mutex is created
 * using xSemaphoreCreateMutex() then the required memory is automatically
 * dynamically allocated inside the xSemaphoreCreateMutex() function.  (see
 * http://www.freertos.org/a00111.html).  If a mutex is created using
 * xSemaphoreCreateMutexStatic() then the application writer must provided the
 * memory.  xSemaphoreCreateMutexStatic() therefore allows a mutex to be created
 * without using any dynamic memory allocation.
 *
 * Mutexes created using this function can be accessed using the xSemaphoreTake()
 * and xSemaphoreGive() macros.  The xSemaphoreTakeRecursive() and
 * xSemaphoreGiveRecursive() macros must not be used.
 *
 * This type of semaphore uses a priority inheritance mechanism so a task
 * 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the
 * semaphore it is no longer required.
 *
 * Mutex type semaphores cannot be used from within interrupt service routines.
 *
 * See xSemaphoreCreateBinary() for an alternative implementation that can be
 * used for pure synchronisation (where one task or interrupt always 'gives' the
 * semaphore and another always 'takes' the semaphore) and from within interrupt
 * service routines.
 *
 * @param pxMutexBuffer Must point to a variable of type StaticSemaphore_t,
 * which will be used to hold the mutex's data structure, removing the need for
 * the memory to be allocated dynamically.
 *
 * @return If the mutex was successfully created then a handle to the created
 * mutex is returned.  If pxMutexBuffer was NULL then NULL is returned.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore;
 StaticSemaphore_t xMutexBuffer;

 void vATask( void * pvParameters )
 {
    // A mutex cannot be used before it has been created.  xMutexBuffer is
    // into xSemaphoreCreateMutexStatic() so no dynamic memory allocation is
    // attempted.
    xSemaphore = xSemaphoreCreateMutexStatic( &xMutexBuffer );

    // As no dynamic memory allocation was performed, xSemaphore cannot be NULL,
    // so there is no need to check it.
 }
 </pre>
 * \defgroup xSemaphoreCreateMutexStatic xSemaphoreCreateMutexStatic
 * \ingroup Semaphores
 */
 #if( configSUPPORT_STATIC_ALLOCATION == 1 )
	#define xSemaphoreCreateMutexStatic( pxMutexBuffer ) xQueueCreateMutexStatic( queueQUEUE_TYPE_MUTEX, ( pxMutexBuffer ) )
#endif /* configSUPPORT_STATIC_ALLOCATION */


/**
 * semphr. h
 * <pre>SemaphoreHandle_t xSemaphoreCreateRecursiveMutex( void )</pre>
 *
 * Creates a new recursive mutex type semaphore instance, and returns a handle
 * by which the new recursive mutex can be referenced.
 *
 * Internally, within the FreeRTOS implementation, recursive mutexs use a block
 * of memory, in which the mutex structure is stored.  If a recursive mutex is
 * created using xSemaphoreCreateRecursiveMutex() then the required memory is
 * automatically dynamically allocated inside the
 * xSemaphoreCreateRecursiveMutex() function.  (see
 * http://www.freertos.org/a00111.html).  If a recursive mutex is created using
 * xSemaphoreCreateRecursiveMutexStatic() then the application writer must
 * provide the memory that will get used by the mutex.
 * xSemaphoreCreateRecursiveMutexStatic() therefore allows a recursive mutex to
 * be created without using any dynamic memory allocation.
 *
 * Mutexes created using this macro can be accessed using the
 * xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros.  The
 * xSemaphoreTake() and xSemaphoreGive() macros must not be used.
 *
 * A mutex used recursively can be 'taken' repeatedly by the owner. The mutex
 * doesn't become available again until the owner has called
 * xSemaphoreGiveRecursive() for each successful 'take' request.  For example,
 * if a task successfully 'takes' the same mutex 5 times then the mutex will
 * not be available to any other task until it has also  'given' the mutex back
 * exactly five times.
 *
 * This type of semaphore uses a priority inheritance mechanism so a task
 * 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the
 * semaphore it is no longer required.
 *
 * Mutex type semaphores cannot be used from within interrupt service routines.
 *
 * See xSemaphoreCreateBinary() for an alternative implementation that can be
 * used for pure synchronisation (where one task or interrupt always 'gives' the
 * semaphore and another always 'takes' the semaphore) and from within interrupt
 * service routines.
 *
 * @return xSemaphore Handle to the created mutex semaphore.  Should be of type
 * SemaphoreHandle_t.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore;

 void vATask( void * pvParameters )
 {
    // Semaphore cannot be used before a call to xSemaphoreCreateMutex().
    // This is a macro so pass the variable in directly.
    xSemaphore = xSemaphoreCreateRecursiveMutex();

    if( xSemaphore != NULL )
    {
        // The semaphore was created successfully.
        // The semaphore can now be used.
    }
 }
 </pre>
 * \defgroup xSemaphoreCreateRecursiveMutex xSemaphoreCreateRecursiveMutex
 * \ingroup Semaphores
 */
#if( ( configSUPPORT_DYNAMIC_ALLOCATION == 1 ) && ( configUSE_RECURSIVE_MUTEXES == 1 ) )
	#define xSemaphoreCreateRecursiveMutex() xQueueCreateMutex( queueQUEUE_TYPE_RECURSIVE_MUTEX )
#endif

/**
 * semphr. h
 * <pre>SemaphoreHandle_t xSemaphoreCreateRecursiveMutexStatic( StaticSemaphore_t *pxMutexBuffer )</pre>
 *
 * Creates a new recursive mutex type semaphore instance, and returns a handle
 * by which the new recursive mutex can be referenced.
 *
 * Internally, within the FreeRTOS implementation, recursive mutexs use a block
 * of memory, in which the mutex structure is stored.  If a recursive mutex is
 * created using xSemaphoreCreateRecursiveMutex() then the required memory is
 * automatically dynamically allocated inside the
 * xSemaphoreCreateRecursiveMutex() function.  (see
 * http://www.freertos.org/a00111.html).  If a recursive mutex is created using
 * xSemaphoreCreateRecursiveMutexStatic() then the application writer must
 * provide the memory that will get used by the mutex.
 * xSemaphoreCreateRecursiveMutexStatic() therefore allows a recursive mutex to
 * be created without using any dynamic memory allocation.
 *
 * Mutexes created using this macro can be accessed using the
 * xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros.  The
 * xSemaphoreTake() and xSemaphoreGive() macros must not be used.
 *
 * A mutex used recursively can be 'taken' repeatedly by the owner. The mutex
 * doesn't become available again until the owner has called
 * xSemaphoreGiveRecursive() for each successful 'take' request.  For example,
 * if a task successfully 'takes' the same mutex 5 times then the mutex will
 * not be available to any other task until it has also  'given' the mutex back
 * exactly five times.
 *
 * This type of semaphore uses a priority inheritance mechanism so a task
 * 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the
 * semaphore it is no longer required.
 *
 * Mutex type semaphores cannot be used from within interrupt service routines.
 *
 * See xSemaphoreCreateBinary() for an alternative implementation that can be
 * used for pure synchronisation (where one task or interrupt always 'gives' the
 * semaphore and another always 'takes' the semaphore) and from within interrupt
 * service routines.
 *
 * @param pxMutexBuffer Must point to a variable of type StaticSemaphore_t,
 * which will then be used to hold the recursive mutex's data structure,
 * removing the need for the memory to be allocated dynamically.
 *
 * @return If the recursive mutex was successfully created then a handle to the
 * created recursive mutex is returned.  If pxMutexBuffer was NULL then NULL is
 * returned.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore;
 StaticSemaphore_t xMutexBuffer;

 void vATask( void * pvParameters )
 {
    // A recursive semaphore cannot be used before it is created.  Here a
    // recursive mutex is created using xSemaphoreCreateRecursiveMutexStatic().
    // The address of xMutexBuffer is passed into the function, and will hold
    // the mutexes data structures - so no dynamic memory allocation will be
    // attempted.
    xSemaphore = xSemaphoreCreateRecursiveMutexStatic( &xMutexBuffer );

    // As no dynamic memory allocation was performed, xSemaphore cannot be NULL,
    // so there is no need to check it.
 }
 </pre>
 * \defgroup xSemaphoreCreateRecursiveMutexStatic xSemaphoreCreateRecursiveMutexStatic
 * \ingroup Semaphores
 */
#if( ( configSUPPORT_STATIC_ALLOCATION == 1 ) && ( configUSE_RECURSIVE_MUTEXES == 1 ) )
	#define xSemaphoreCreateRecursiveMutexStatic( pxStaticSemaphore ) xQueueCreateMutexStatic( queueQUEUE_TYPE_RECURSIVE_MUTEX, pxStaticSemaphore )
#endif /* configSUPPORT_STATIC_ALLOCATION */

/**
 * semphr. h
 * <pre>SemaphoreHandle_t xSemaphoreCreateCounting( UBaseType_t uxMaxCount, UBaseType_t uxInitialCount )</pre>
 *
 * Creates a new counting semaphore instance, and returns a handle by which the
 * new counting semaphore can be referenced.
 *
 * In many usage scenarios it is faster and more memory efficient to use a
 * direct to task notification in place of a counting semaphore!
 * http://www.freertos.org/RTOS-task-notifications.html
 *
 * Internally, within the FreeRTOS implementation, counting semaphores use a
 * block of memory, in which the counting semaphore structure is stored.  If a
 * counting semaphore is created using xSemaphoreCreateCounting() then the
 * required memory is automatically dynamically allocated inside the
 * xSemaphoreCreateCounting() function.  (see
 * http://www.freertos.org/a00111.html).  If a counting semaphore is created
 * using xSemaphoreCreateCountingStatic() then the application writer can
 * instead optionally provide the memory that will get used by the counting
 * semaphore.  xSemaphoreCreateCountingStatic() therefore allows a counting
 * semaphore to be created without using any dynamic memory allocation.
 *
 * Counting semaphores are typically used for two things:
 *
 * 1) Counting events.
 *
 *    In this usage scenario an event handler will 'give' a semaphore each time
 *    an event occurs (incrementing the semaphore count value), and a handler
 *    task will 'take' a semaphore each time it processes an event
 *    (decrementing the semaphore count value).  The count value is therefore
 *    the difference between the number of events that have occurred and the
 *    number that have been processed.  In this case it is desirable for the
 *    initial count value to be zero.
 *
 * 2) Resource management.
 *
 *    In this usage scenario the count value indicates the number of resources
 *    available.  To obtain control of a resource a task must first obtain a
 *    semaphore - decrementing the semaphore count value.  When the count value
 *    reaches zero there are no free resources.  When a task finishes with the
 *    resource it 'gives' the semaphore back - incrementing the semaphore count
 *    value.  In this case it is desirable for the initial count value to be
 *    equal to the maximum count value, indicating that all resources are free.
 *
 * @param uxMaxCount The maximum count value that can be reached.  When the
 *        semaphore reaches this value it can no longer be 'given'.
 *
 * @param uxInitialCount The count value assigned to the semaphore when it is
 *        created.
 *
 * @return Handle to the created semaphore.  Null if the semaphore could not be
 *         created.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore;

 void vATask( void * pvParameters )
 {
 SemaphoreHandle_t xSemaphore = NULL;

    // Semaphore cannot be used before a call to xSemaphoreCreateCounting().
    // The max value to which the semaphore can count should be 10, and the
    // initial value assigned to the count should be 0.
    xSemaphore = xSemaphoreCreateCounting( 10, 0 );

    if( xSemaphore != NULL )
    {
        // The semaphore was created successfully.
        // The semaphore can now be used.
    }
 }
 </pre>
 * \defgroup xSemaphoreCreateCounting xSemaphoreCreateCounting
 * \ingroup Semaphores
 */
#if( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
	#define xSemaphoreCreateCounting( uxMaxCount, uxInitialCount ) xQueueCreateCountingSemaphore( ( uxMaxCount ), ( uxInitialCount ) )
#endif

/**
 * semphr. h
 * <pre>SemaphoreHandle_t xSemaphoreCreateCountingStatic( UBaseType_t uxMaxCount, UBaseType_t uxInitialCount, StaticSemaphore_t *pxSemaphoreBuffer )</pre>
 *
 * Creates a new counting semaphore instance, and returns a handle by which the
 * new counting semaphore can be referenced.
 *
 * In many usage scenarios it is faster and more memory efficient to use a
 * direct to task notification in place of a counting semaphore!
 * http://www.freertos.org/RTOS-task-notifications.html
 *
 * Internally, within the FreeRTOS implementation, counting semaphores use a
 * block of memory, in which the counting semaphore structure is stored.  If a
 * counting semaphore is created using xSemaphoreCreateCounting() then the
 * required memory is automatically dynamically allocated inside the
 * xSemaphoreCreateCounting() function.  (see
 * http://www.freertos.org/a00111.html).  If a counting semaphore is created
 * using xSemaphoreCreateCountingStatic() then the application writer must
 * provide the memory.  xSemaphoreCreateCountingStatic() therefore allows a
 * counting semaphore to be created without using any dynamic memory allocation.
 *
 * Counting semaphores are typically used for two things:
 *
 * 1) Counting events.
 *
 *    In this usage scenario an event handler will 'give' a semaphore each time
 *    an event occurs (incrementing the semaphore count value), and a handler
 *    task will 'take' a semaphore each time it processes an event
 *    (decrementing the semaphore count value).  The count value is therefore
 *    the difference between the number of events that have occurred and the
 *    number that have been processed.  In this case it is desirable for the
 *    initial count value to be zero.
 *
 * 2) Resource management.
 *
 *    In this usage scenario the count value indicates the number of resources
 *    available.  To obtain control of a resource a task must first obtain a
 *    semaphore - decrementing the semaphore count value.  When the count value
 *    reaches zero there are no free resources.  When a task finishes with the
 *    resource it 'gives' the semaphore back - incrementing the semaphore count
 *    value.  In this case it is desirable for the initial count value to be
 *    equal to the maximum count value, indicating that all resources are free.
 *
 * @param uxMaxCount The maximum count value that can be reached.  When the
 *        semaphore reaches this value it can no longer be 'given'.
 *
 * @param uxInitialCount The count value assigned to the semaphore when it is
 *        created.
 *
 * @param pxSemaphoreBuffer Must point to a variable of type StaticSemaphore_t,
 * which will then be used to hold the semaphore's data structure, removing the
 * need for the memory to be allocated dynamically.
 *
 * @return If the counting semaphore was successfully created then a handle to
 * the created counting semaphore is returned.  If pxSemaphoreBuffer was NULL
 * then NULL is returned.
 *
 * Example usage:
 <pre>
 SemaphoreHandle_t xSemaphore;
 StaticSemaphore_t xSemaphoreBuffer;

 void vATask( void * pvParameters )
 {
 SemaphoreHandle_t xSemaphore = NULL;

    // Counting semaphore cannot be used before they have been created.  Create
    // a counting semaphore using xSemaphoreCreateCountingStatic().  The max
    // value to which the semaphore can count is 10, and the initial value
    // assigned to the count will be 0.  The address of xSemaphoreBuffer is
    // passed in and will be used to hold the semaphore structure, so no dynamic
    // memory allocation will be used.
    xSemaphore = xSemaphoreCreateCounting( 10, 0, &xSemaphoreBuffer );

    // No memory allocation was attempted so xSemaphore cannot be NULL, so there
    // is no need to check its value.
 }
 </pre>
 * \defgroup xSemaphoreCreateCountingStatic xSemaphoreCreateCountingStatic
 * \ingroup Semaphores
 */
#if( configSUPPORT_STATIC_ALLOCATION == 1 )
	#define xSemaphoreCreateCountingStatic( uxMaxCount, uxInitialCount, pxSemaphoreBuffer ) xQueueCreateCountingSemaphoreStatic( ( uxMaxCount ), ( uxInitialCount ), ( pxSemaphoreBuffer ) )
#endif /* configSUPPORT_STATIC_ALLOCATION */

/**
 * semphr. h
 * <pre>void vSemaphoreDelete( SemaphoreHandle_t xSemaphore );</pre>
 *
 * Delete a semaphore.  This function must be used with care.  For example,
 * do not delete a mutex type semaphore if the mutex is held by a task.
 *
 * @param xSemaphore A handle to the semaphore to be deleted.
 *
 * \defgroup vSemaphoreDelete vSemaphoreDelete
 * \ingroup Semaphores
 */
#define vSemaphoreDelete( xSemaphore ) vQueueDelete( ( QueueHandle_t ) ( xSemaphore ) )

/**
 * semphr.h
 * <pre>TaskHandle_t xSemaphoreGetMutexHolder( SemaphoreHandle_t xMutex );</pre>
 *
 * If xMutex is indeed a mutex type semaphore, return the current mutex holder.
 * If xMutex is not a mutex type semaphore, or the mutex is available (not held
 * by a task), return NULL.
 *
 * Note: This is a good way of determining if the calling task is the mutex
 * holder, but not a good way of determining the identity of the mutex holder as
 * the holder may change between the function exiting and the returned value
 * being tested.
 */
#define xSemaphoreGetMutexHolder( xSemaphore ) xQueueGetMutexHolder( ( xSemaphore ) )

/**
 * semphr.h
 * <pre>UBaseType_t uxSemaphoreGetCount( SemaphoreHandle_t xSemaphore );</pre>
 *
 * If the semaphore is a counting semaphore then uxSemaphoreGetCount() returns
 * its current count value.  If the semaphore is a binary semaphore then
 * uxSemaphoreGetCount() returns 1 if the semaphore is available, and 0 if the
 * semaphore is not available.
 *
 */
#define uxSemaphoreGetCount( xSemaphore ) uxQueueMessagesWaiting( ( QueueHandle_t ) ( xSemaphore ) )

#endif /* SEMAPHORE_H */