Diff: FreeRTOS/Source/include/semphr.h

Revision:

0:d4960fcea8ff

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/FreeRTOS/Source/include/semphr.h	Sat Jan 01 11:17:45 2011 +0000
@@ -0,0 +1,711 @@
+/*
+    FreeRTOS V6.0.3 - Copyright (C) 2010 Real Time Engineers Ltd.
+
+    ***************************************************************************
+    *                                                                         *
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+
+    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 exception 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.
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+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
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+    can be viewed here: http://www.freertos.org/a00114.html and also obtained 
+    by writing to Richard Barry, contact details for whom are available on the
+    FreeRTOS WEB site.
+
+    1 tab == 4 spaces!
+
+    http://www.FreeRTOS.org - Documentation, latest information, license and
+    contact details.
+
+    http://www.SafeRTOS.com - A version that is certified for use in safety
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+
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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 char ) 1 )
+#define semSEMAPHORE_QUEUE_ITEM_LENGTH        ( ( unsigned char ) 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
+ * <pre>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.
+ * 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, 
+                          signed 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 char ucLocalTickCount = 0;
+ static signed 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 */
+
+