semphr.h

这是一个FreeRTOS(V511)的移植程序,MCU为FREESCALE公司的MC9S08AW60

 * 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>
 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( xMutex, ( 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, 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
 */
#define xSemaphoreGiveRecursive( xMutex )	xQueueGiveMutexRecursive( xMutex )

/* 
 * xSemaphoreAltGive() is an alternative version of xSemaphoreGive().
 *
 * 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 xSemaphoreAltGive( xSemaphore )		xQueueAltGenericSend( ( xQueueHandle ) xSemaphore, NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK )

/**
 * semphr. h
 * <pre>
 xSemaphoreGiveFromISR( 
                          xSemaphoreHandle xSemaphore, 
                          portBASE_TYPE *pxHigherPriorityTaskWoken
                      )</pre>
 *
 * <i>Macro</i> to  release a semaphore.  The semaphore must have previously been
 * created with a call to vSemaphoreCreateBinary() 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
 xSemaphoreHandle 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 unsigned portCHAR ucLocalTickCount = 0;
 static portBASE_TYPE 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 )			xQueueGenericSendFromISR( ( xQueueHandle ) xSemaphore, NULL, pxHigherPriorityTaskWoken, queueSEND_TO_BACK )

/**
 * semphr. h
 * <pre>xSemaphoreHandle xSemaphoreCreateMutex( void )</pre>
 *
 * <i>Macro</i> that implements a mutex semaphore by using the existing queue 
 * mechanism.
 *
 * Mutexes created using this macro can be accessed using the xSemaphoreTake()
 * and xSemaphoreGive() macros.  The xSemaphoreTakeRecursive() and 
 * xSemaphoreGiveRecursive() macros should 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 vSemaphoreCreateBinary() 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 
 *		xSemaphoreHandle.
 *
 * Example usage:
 <pre>
 xSemaphoreHandle 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 vSemaphoreCreateMutex vSemaphoreCreateMutex
 * \ingroup Semaphores
 */
#define xSemaphoreCreateMutex() xQueueCreateMutex()


/**
 * semphr. h
 * <pre>xSemaphoreHandle xSemaphoreCreateRecursiveMutex( void )</pre>
 *
 * <i>Macro</i> that implements a recursive mutex by using the existing queue 
 * mechanism.
 *
 * Mutexes created using this macro can be accessed using the 
 * xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros.  The 
 * xSemaphoreTake() and xSemaphoreGive() macros should 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 vSemaphoreCreateBinary() 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 
 *		xSemaphoreHandle.
 *
 * Example usage:
 <pre>
 xSemaphoreHandle 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 vSemaphoreCreateMutex vSemaphoreCreateMutex
 * \ingroup Semaphores
 */
#define xSemaphoreCreateRecursiveMutex() xQueueCreateMutex()

/**
 * semphr. h
 * <pre>xSemaphoreHandle xSemaphoreCreateCounting( unsigned portBASE_TYPE uxMaxCount, unsigned portBASE_TYPE uxInitialCount )</pre>
 *
 * <i>Macro</i> that creates a counting semaphore by using the existing 
 * queue mechanism.  
 *
 * 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>
 xSemaphoreHandle xSemaphore;

 void vATask( void * pvParameters )
 {
 xSemaphoreHandle 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
 */
#define xSemaphoreCreateCounting( uxMaxCount, uxInitialCount ) xQueueCreateCountingSemaphore( uxMaxCount, uxInitialCount )


#endif /* SEMAPHORE_H */