/*
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*/

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

#ifndef SEMAPHORE_H
#define SEMAPHORE_H

#include "queue.h"

typedef xQueueHandle xSemaphoreHandle;

#define semBINARY_SEMAPHORE_QUEUE_LENGTH	( ( unsigned portCHAR ) 1 )
#define semSEMAPHORE_QUEUE_ITEM_LENGTH		( ( unsigned portCHAR ) 0 )
#define semGIVE_BLOCK_TIME					( ( portTickType ) 0 )


/**
 * semphr. h
 * <pre>vSemaphoreCreateBinary( xSemaphoreHandle xSemaphore )</pre>
 *
 * <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 xSemaphoreHandle.
 *
 * Example usage:
 <pre>
 xSemaphoreHandle xSemaphore;

 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
 */
#define vSemaphoreCreateBinary( xSemaphore )		{																								\
														xSemaphore = xQueueCreate( ( unsigned portBASE_TYPE ) 1, semSEMAPHORE_QUEUE_ITEM_LENGTH );	\
														if( xSemaphore != NULL )																	\
														{																							\
															xSemaphoreGive( xSemaphore );															\
														}																							\
													}

/**
 * semphr. h
 * xSemaphoreTake( 
 *                   xSemaphoreHandle xSemaphore, 
 *                   portTickType xBlockTime 
 *               )</pre>
 *
 * <i>Macro</i> to obtain a semaphore.  The semaphore must have previously been
 * created with a call to vSemaphoreCreateBinary(), 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_RATE_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>
 xSemaphoreHandle xSemaphore = NULL;

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

 // 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, ( portTickType ) 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( ( xQueueHandle ) xSemaphore, NULL, xBlockTime, pdFALSE )

/**
 * semphr. h
 * xSemaphoreTakeRecursive( 
 *                          xSemaphoreHandle xMutex, 
 *                          portTickType 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_RATE_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>
 xSemaphoreHandle 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, ( portTickType ) 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, ( portTickType ) 10 );
            xSemaphoreTakeRecursive( xMutex, ( portTickType ) 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
 */
#define xSemaphoreTakeRecursive( xMutex, xBlockTime )	xQueueTakeMutexRecursive( xMutex, xBlockTime )


/* 
 * xSemaphoreAltTake() is an alternative version of xSemaphoreTake().
 *
 * The source code that implements the alternative (Alt) API is much 
 * simpler	because it executes everything from within a critical section.  
 * This is	the approach taken by many other RTOSes, but FreeRTOS.org has the 
 * preferred fully featured API too.  The fully featured API has more 
 * complex	code that takes longer to execute, but makes much less use of 
 * critical sections.  Therefore the alternative API sacrifices interrupt 
 * responsiveness to gain execution speed, whereas the fully featured API
 * sacrifices execution speed to ensure better interrupt responsiveness.
 */
#define xSemaphoreAltTake( xSemaphore, xBlockTime )		xQueueAltGenericReceive( ( xQueueHandle ) xSemaphore, NULL, xBlockTime, pdFALSE )

/**
 * semphr. h
 * <pre>xSemaphoreGive( xSemaphoreHandle xSemaphore )</pre>
 *
 * <i>Macro</i> to release a semaphore.  The semaphore must have previously been
 * created with a call to vSemaphoreCreateBinary(), 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>
 xSemaphoreHandle xSemaphore = NULL;

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

    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, ( portTickType ) 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( ( xQueueHandle ) xSemaphore, NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK )

/**
 * semphr. h
 * <pre>xSemaphoreGiveRecursive( xSemaphoreHandle xMutex )</pre>
 *
 * <i>Macro</i> to recursively release, or 'give', a mutex type semaphore.