From d291e583a5ee10f13b0f4039a8d114e15799eb7b Mon Sep 17 00:00:00 2001 From: Pixel Date: Sun, 23 Jan 2011 12:15:10 -0800 Subject: Adding basic FreeRTOS sourcetree; v6.1.1 currently. --- FreeRTOS/Source/include/semphr.h | 711 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 711 insertions(+) create mode 100644 FreeRTOS/Source/include/semphr.h (limited to 'FreeRTOS/Source/include/semphr.h') diff --git a/FreeRTOS/Source/include/semphr.h b/FreeRTOS/Source/include/semphr.h new file mode 100644 index 0000000..8674096 --- /dev/null +++ b/FreeRTOS/Source/include/semphr.h @@ -0,0 +1,711 @@ +/* + FreeRTOS V6.1.1 - Copyright (C) 2011 Real Time Engineers Ltd. + + *************************************************************************** + * * + * If you are: * + * * + * + New to FreeRTOS, * + * + Wanting to learn FreeRTOS or multitasking in general quickly * + * + Looking for basic training, * + * + Wanting to improve your FreeRTOS skills and productivity * + * * + * then take a look at the FreeRTOS books - available as PDF or paperback * + * * + * "Using the FreeRTOS Real Time Kernel - a Practical Guide" * + * http://www.FreeRTOS.org/Documentation * + * * + * A pdf reference manual is also available. Both are usually delivered * + * to your inbox within 20 minutes to two hours when purchased between 8am * + * and 8pm GMT (although please allow up to 24 hours in case of * + * exceptional circumstances). Thank you for your support! * + * * + *************************************************************************** + + 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. + 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. See the GNU General Public License for + more details. You should have received a copy of the GNU General Public + License and the FreeRTOS license exception along with FreeRTOS; if not it + 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 + critical systems. + + http://www.OpenRTOS.com - Commercial support, development, porting, + licensing and training services. +*/ + +#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 + * 
vSemaphoreCreateBinary( xSemaphoreHandle xSemaphore )
+ * + * Macro 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: + 
+ 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.  
+    }
+ }
+
+ * \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 
+ *               )
+ * + * Macro 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: + 
+ 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.
+        }
+    }
+ }
+
+ * \defgroup xSemaphoreTake xSemaphoreTake + * \ingroup Semaphores + */ +#define xSemaphoreTake( xSemaphore, xBlockTime ) xQueueGenericReceive( ( xQueueHandle ) xSemaphore, NULL, xBlockTime, pdFALSE ) + +/** + * semphr. h + * xSemaphoreTakeRecursive( + * xSemaphoreHandle xMutex, + * portTickType xBlockTime + * ) + * + * Macro 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: + 
+ 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.
+        }
+    }
+ }
+
+ * \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 + * 
xSemaphoreGive( xSemaphoreHandle xSemaphore )
+ * + * Macro 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: + 
+ 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.
+            }
+        }
+    }
+ }
+
+ * \defgroup xSemaphoreGive xSemaphoreGive + * \ingroup Semaphores + */ +#define xSemaphoreGive( xSemaphore ) xQueueGenericSend( ( xQueueHandle ) xSemaphore, NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK ) + +/** + * semphr. h + * 
xSemaphoreGiveRecursive( xSemaphoreHandle xMutex )
+ * + * Macro 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: + 
+ 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.
+        }
+    }
+ }
+
+ * \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 + * 
+ xSemaphoreGiveFromISR( 
+                          xSemaphoreHandle xSemaphore, 
+                          signed portBASE_TYPE *pxHigherPriorityTaskWoken
+                      )
+ * + * Macro 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: + 
+ \#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.
+    }
+ }
+
+ * \defgroup xSemaphoreGiveFromISR xSemaphoreGiveFromISR + * \ingroup Semaphores + */ +#define xSemaphoreGiveFromISR( xSemaphore, pxHigherPriorityTaskWoken ) xQueueGenericSendFromISR( ( xQueueHandle ) xSemaphore, NULL, pxHigherPriorityTaskWoken, queueSEND_TO_BACK ) + +/** + * semphr. h + * 
xSemaphoreHandle xSemaphoreCreateMutex( void )
+ * + * Macro 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: + 
+ 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.  
+    }
+ }
+
+ * \defgroup vSemaphoreCreateMutex vSemaphoreCreateMutex + * \ingroup Semaphores + */ +#define xSemaphoreCreateMutex() xQueueCreateMutex() + + +/** + * semphr. h + * 
xSemaphoreHandle xSemaphoreCreateRecursiveMutex( void )
+ * + * Macro 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: + 
+ 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.  
+    }
+ }
+
+ * \defgroup vSemaphoreCreateMutex vSemaphoreCreateMutex + * \ingroup Semaphores + */ +#define xSemaphoreCreateRecursiveMutex() xQueueCreateMutex() + +/** + * semphr. h + * 
xSemaphoreHandle xSemaphoreCreateCounting( unsigned portBASE_TYPE uxMaxCount, unsigned portBASE_TYPE uxInitialCount )
+ * + * Macro 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: + 
+ 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.  
+    }
+ }
+
+ * \defgroup xSemaphoreCreateCounting xSemaphoreCreateCounting + * \ingroup Semaphores + */ +#define xSemaphoreCreateCounting( uxMaxCount, uxInitialCount ) xQueueCreateCountingSemaphore( uxMaxCount, uxInitialCount ) + + +#endif /* SEMAPHORE_H */ + + -- cgit v1.2.3