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Documentation updates.
This commit is contained in:
Richard Barry
parent
c4edb21f63
commit
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@ -37,11 +37,10 @@
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/*
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The tasks defined on this page demonstrate the use of recursive mutexes.
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All mutexes are created using a call to xSemaphoreCreateMutex(). For
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recursive mutex functionality the created mutex should then be manipulated
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For recursive mutex functionality the created mutex should be created using
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xSemaphoreCreateRecursiveMutex(), then be manipulated
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using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() API
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functions. Recursive mutexes must NOT be passed as a parameter to the
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standard mutex API functions xSemaphoreTake() and xSemaphoreGive().
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functions.
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This demo creates three tasks all of which access the same recursive mutex:
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@ -99,18 +99,21 @@ typedef xQueueHandle xSemaphoreHandle;
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* portTickType xBlockTime
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* )</pre>
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*
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* <i>Macro</i> to obtain a semaphore. The semaphore must of been created using
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* vSemaphoreCreateBinary ().
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* <i>Macro</i> to obtain a semaphore. The semaphore must have previously been
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* created with a call to vSemaphoreCreateBinary(), xSemaphoreCreateMutex() or
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* xSemaphoreCreateCounting().
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*
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* @param xSemaphore A handle to the semaphore being obtained. This is the
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* handle returned by vSemaphoreCreateBinary ();
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* @param xSemaphore A handle to the semaphore being taken - obtained when
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* the semaophore was created.
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*
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* @param xBlockTime The time in ticks to wait for the semaphore to become
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* available. The macro portTICK_RATE_MS can be used to convert this to a
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* real time. A block time of zero can be used to poll the semaphore.
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* real time. A block time of zero can be used to poll the semaphore. A block
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* time of portMAX_DELAY can be used to block indefinately (provided
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* INCLUDE_vTaskSuspend is set to 1 in FreeRTOSConfig.h).
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*
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* @return pdTRUE if the semaphore was obtained. pdFALSE if xBlockTime
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* expired without the semaphore becoming available.
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* @return pdTRUE if the semaphore was obtained. pdFALSE
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* if xBlockTime expired without the semaphore becoming available.
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*
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* Example usage:
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<pre>
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@ -156,6 +159,100 @@ typedef xQueueHandle xSemaphoreHandle;
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*/
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#define xSemaphoreTake( xSemaphore, xBlockTime ) xQueueGenericReceive( ( xQueueHandle ) xSemaphore, NULL, xBlockTime, pdFALSE )
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/**
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* semphr. h
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* xSemaphoreTakeRecursive(
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* xSemaphoreHandle xMutex,
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* portTickType xBlockTime
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* )
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*
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* <i>Macro</i> to recursively obtain, or 'take', a mutex type semaphore.
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* The mutex must have previously been created using a call to
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* xSemaphoreCreateRecursiveMutex();
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*
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* configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this
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* macro to be available.
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*
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* This macro must not be used on mutexes created using xSemaphoreCreateMutex().
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*
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* A mutex used recursively can be 'taken' repeatedly by the owner. The mutex
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* doesn't become available again until the owner has called
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* xSemaphoreGiveRecursive() for each successful 'take' request. For example,
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* if a task successfully 'takes' the same mutex 5 times then the mutex will
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* not be avilable to any other task until it has also 'given' the mutex back
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* exactly five times.
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*
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* @param xMutex A handle to the mutex being obtained. This is the
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* handle returned by xSemaphoreCreateMutex();
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*
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* @param xBlockTime The time in ticks to wait for the semaphore to become
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* available. The macro portTICK_RATE_MS can be used to convert this to a
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* real time. A block time of zero can be used to poll the semaphore. If
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* the task already owns the semaphore then xSemaphoreTakeRecursive() will
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* return immediately nomatter what the value of xBlockTime.
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*
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* @return pdTRUE if the semaphore was obtained. pdFALSE if xBlockTime
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* expired without the semaphore becoming available.
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*
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* Example usage:
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<pre>
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xSemaphoreHandle xMutex = NULL;
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// A task that creates a mutex.
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void vATask( void * pvParameters )
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{
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// Create the mutex to guard a shared resource.
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xMutex = xSemaphoreCreateRecursiveMutex();
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}
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// A task that uses the mutex.
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void vAnotherTask( void * pvParameters )
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{
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// ... Do other things.
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if( xMutex != NULL )
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{
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// See if we can obtain the mutex. If the mutex is not available
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// wait 10 ticks to see if it becomes free.
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if( xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 ) == pdTRUE )
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{
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// We were able to obtain the mutex and can now access the
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// shared resource.
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// ...
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// For some reason due to the nature of the code further calls to
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// xSemaphoreTakeRecursive() are made on the same mutex. In real
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// code these would not be just sequential calls as this would make
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// no sense. Instead the calls are likely to be buried inside
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// a more complex call structure.
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xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 );
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xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 );
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// The mutex has now been 'taken' three times, so will not be
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// available to another task until it has also been given back
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// three times. Again it is unlikely that real code would have
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// these calls sequentially, but instead buried in a more complex
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// call structure. This is just for illustrative puproses.
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xSemaphoreGiveRecursive( xSemaphore );
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xSemaphoreGiveRecursive( xSemaphore );
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xSemaphoreGiveRecursive( xSemaphore );
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// Now the mutex can be taken by other tasks.
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}
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else
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{
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// We could not obtain the mutex and can therefore not access
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// the shared resource safely.
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}
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}
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}
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</pre>
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* \defgroup xSemaphoreTakeRecursive xSemaphoreTakeRecursive
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* \ingroup Semaphores
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*/
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#define xSemaphoreTakeRecursive( xMutex, xBlockTime ) xQueueTakeMutexRecursive( xMutex, xBlockTime )
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/*
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* xSemaphoreAltTake() is an alternative version of xSemaphoreTake().
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*
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@ -174,14 +271,18 @@ typedef xQueueHandle xSemaphoreHandle;
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* semphr. h
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* <pre>xSemaphoreGive( xSemaphoreHandle xSemaphore )</pre>
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*
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* <i>Macro</i> to release a semaphore. The semaphore must of been created using
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* vSemaphoreCreateBinary (), and obtained using sSemaphoreTake ().
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* <i>Macro</i> to release a semaphore. The semaphore must have previously been
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* created with a call to vSemaphoreCreateBinary(), xSemaphoreCreateMutex() or
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* xSemaphoreCreateCounting(). and obtained using sSemaphoreTake().
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*
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* This must not be used from an ISR. See xSemaphoreGiveFromISR () for
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* This macro must not be used from an ISR. See xSemaphoreGiveFromISR () for
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* an alternative which can be used from an ISR.
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*
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* This macro must also not be used on semaphores created using
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* xSemaphoreCreateRecursiveMutex().
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*
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* @param xSemaphore A handle to the semaphore being released. This is the
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* handle returned by vSemaphoreCreateBinary ();
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* handle returned when the semaphore was created.
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*
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* @return pdTRUE if the semaphore was released. pdFALSE if an error occurred.
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* Semaphores are implemented using queues. An error can occur if there is
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@ -229,6 +330,90 @@ typedef xQueueHandle xSemaphoreHandle;
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*/
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#define xSemaphoreGive( xSemaphore ) xQueueGenericSend( ( xQueueHandle ) xSemaphore, NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK )
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/**
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* semphr. h
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* <pre>xSemaphoreGiveRecursive( xSemaphoreHandle xSemaphore )</pre>
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*
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* <i>Macro</i> to recursively release, or 'give', a mutex type semaphore.
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* The mutex must have previously been created using a call to
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* xSemaphoreCreateRecursiveMutex();
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*
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* configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this
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* macro to be available.
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*
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* This macro must not be used on mutexes created using xSemaphoreCreateMutex().
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*
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* A mutex used recursively can be 'taken' repeatedly by the owner. The mutex
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* doesn't become available again until the owner has called
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* xSemaphoreGiveRecursive() for each successful 'take' request. For example,
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* if a task successfully 'takes' the same mutex 5 times then the mutex will
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* not be avilable to any other task until it has also 'given' the mutex back
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* exactly five times.
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*
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* @param xMutex A handle to the mutex being released, or 'given'. This is the
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* handle returned by xSemaphoreCreateMutex();
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*
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* @return pdTRUE if the semaphore was given.
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*
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* Example usage:
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<pre>
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xSemaphoreHandle xMutex = NULL;
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// A task that creates a mutex.
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void vATask( void * pvParameters )
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{
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// Create the mutex to guard a shared resource.
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xMutex = xSemaphoreCreateRecursiveMutex();
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}
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// A task that uses the mutex.
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void vAnotherTask( void * pvParameters )
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{
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// ... Do other things.
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if( xMutex != NULL )
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{
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// See if we can obtain the mutex. If the mutex is not available
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// wait 10 ticks to see if it becomes free.
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if( xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 ) == pdTRUE )
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{
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// We were able to obtain the mutex and can now access the
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// shared resource.
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// ...
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// For some reason due to the nature of the code further calls to
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// xSemaphoreTakeRecursive() are made on the same mutex. In real
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// code these would not be just sequential calls as this would make
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// no sense. Instead the calls are likely to be buried inside
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// a more complex call structure.
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xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 );
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xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 );
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// The mutex has now been 'taken' three times, so will not be
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// available to another task until it has also been given back
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// three times. Again it is unlikely that real code would have
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// these calls sequentially, it would be more likely that the calls
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// to xSemaphoreGiveRecursive() would be called as a call stack
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// unwound. This is just for demonstrative purposes.
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xSemaphoreGiveRecursive( xSemaphore );
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xSemaphoreGiveRecursive( xSemaphore );
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xSemaphoreGiveRecursive( xSemaphore );
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// Now the mutex can be taken by other tasks.
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}
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else
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{
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// We could not obtain the mutex and can therefore not access
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// the shared resource safely.
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}
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}
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}
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</pre>
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* \defgroup xSemaphoreGiveRecursive xSemaphoreGiveRecursive
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* \ingroup Semaphores
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*/
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#define xSemaphoreGiveRecursive( xMutex ) xQueueGiveMutexRecursive( xMutex )
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/*
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* xSemaphoreAltGive() is an alternative version of xSemaphoreGive().
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*
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@ -251,8 +436,8 @@ typedef xQueueHandle xSemaphoreHandle;
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portSHORT sTaskPreviouslyWoken
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)</pre>
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*
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* <i>Macro</i> to release a semaphore. The semaphore must of been created using
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* vSemaphoreCreateBinary (), and obtained using xSemaphoreTake ().
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* <i>Macro</i> to release a semaphore. The semaphore must have previously been
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* created with a call to vSemaphoreCreateBinary() or xSemaphoreCreateCounting().
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*
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* Mutex type semaphores (those created using a call to xSemaphoreCreateMutex())
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* must not be used with this macro.
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@ -260,7 +445,7 @@ typedef xQueueHandle xSemaphoreHandle;
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* This macro can be used from an ISR.
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*
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* @param xSemaphore A handle to the semaphore being released. This is the
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* handle returned by vSemaphoreCreateBinary ();
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* handle returned when the semaphore was created.
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*
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* @param sTaskPreviouslyWoken This is included so an ISR can make multiple calls
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* to xSemaphoreGiveFromISR () from a single interrupt. The first call
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@ -283,8 +468,8 @@ typedef xQueueHandle xSemaphoreHandle;
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{
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for( ;; )
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{
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// We want this task to run every 10 ticks or a timer. The semaphore
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// was created before this task was started
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// We want this task to run every 10 ticks of a timer. The semaphore
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// was created before this task was started.
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// Block waiting for the semaphore to become available.
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if( xSemaphoreTake( xSemaphore, LONG_TIME ) == pdTRUE )
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@ -295,7 +480,8 @@ typedef xQueueHandle xSemaphoreHandle;
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// We have finished our task. Return to the top of the loop where
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// we will block on the semaphore until it is time to execute
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// again.
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// again. Note when using the semaphore for synchronisation with an
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// ISR in this manner there is no need to 'give' the semaphore back.
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}
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}
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}
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@ -316,11 +502,18 @@ typedef xQueueHandle xSemaphoreHandle;
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if( ucLocalTickCount >= TICKS_TO_WAIT )
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{
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// Unblock the task by releasing the semaphore.
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xSemaphoreGiveFromISR( xSemaphore, xTaskWoken );
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xTaskWoken = xSemaphoreGiveFromISR( xSemaphore, xTaskWoken );
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// Reset the count so we release the semaphore again in 10 ticks time.
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ucLocalTickCount = 0;
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}
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if( xTaskWoken != pdFALSE )
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{
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// We can force a context switch here. Context switching from an
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// ISR uses port specific syntax. Check the demo task for your port
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// to find the syntax required.
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}
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}
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</pre>
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* \defgroup xSemaphoreGiveFromISR xSemaphoreGiveFromISR
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@ -335,6 +528,10 @@ typedef xQueueHandle xSemaphoreHandle;
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* <i>Macro</i> that implements a mutex semaphore by using the existing queue
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* mechanism.
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*
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* Mutexes created using this macro can be accessed using the xSemaphoreTake()
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* and xSemaphoreGive() macros. The xSemaphoreTakeRecursive() and
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* xSemaphoreGiveRecursive() macros should not be used.
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*
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* This type of semaphore uses a priority inheritance mechanism so a task
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* 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the
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* semaphore it is no longer required.
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@ -370,6 +567,60 @@ typedef xQueueHandle xSemaphoreHandle;
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* \ingroup Semaphores
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*/
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#define xSemaphoreCreateMutex() xQueueCreateMutex()
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/**
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* semphr. h
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* <pre>xSemaphoreHandle xSemaphoreCreateRecursiveMutex( void )</pre>
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*
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* <i>Macro</i> that implements a recursive mutex by using the existing queue
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* mechanism.
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*
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* Mutexes created using this macro can be accessed using the
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* xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros. The
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* xSemaphoreTake() and xSemaphoreGive() macros should not be used.
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*
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* A mutex used recursively can be 'taken' repeatedly by the owner. The mutex
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* doesn't become available again until the owner has called
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* xSemaphoreGiveRecursive() for each successful 'take' request. For example,
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* if a task successfully 'takes' the same mutex 5 times then the mutex will
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* not be avilable to any other task until it has also 'given' the mutex back
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* exactly five times.
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*
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* This type of semaphore uses a priority inheritance mechanism so a task
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* 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the
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* semaphore it is no longer required.
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*
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* Mutex type semaphores cannot be used from within interrupt service routines.
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*
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* See xSemaphoreCreateBinary() for an alternative implementation that can be
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* used for pure synchronisation (where one task or interrupt always 'gives' the
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* semaphore and another always 'takes' the semaphore) and from within interrupt
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* service routines.
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*
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* @return xSemaphore Handle to the created mutex semaphore. Should be of type
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* xSemaphoreHandle.
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*
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* Example usage:
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<pre>
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xSemaphoreHandle xSemaphore;
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void vATask( void * pvParameters )
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{
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// Semaphore cannot be used before a call to xSemaphoreCreateMutex().
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// This is a macro so pass the variable in directly.
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xSemaphore = xSemaphoreCreateRecursiveMutex();
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if( xSemaphore != NULL )
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{
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// The semaphore was created successfully.
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// The semaphore can now be used.
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}
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}
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</pre>
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* \defgroup vSemaphoreCreateMutex vSemaphoreCreateMutex
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* \ingroup Semaphores
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*/
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#define xSemaphoreCreateRecursiveMutex() xQueueCreateMutex()
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/**
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@ -435,8 +686,6 @@ typedef xQueueHandle xSemaphoreHandle;
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*/
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#define xSemaphoreCreateCounting( uxMaxCount, uxInitialCount ) xQueueCreateCountingSemaphore( uxMaxCount, uxInitialCount )
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#define xSemaphoreTakeRecursive( xMutex, xBlockTime ) xQueueTakeMutexRecursive( xMutex, xBlockTime )
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#define xSemaphoreGiveRecursive( xMutex ) xQueueGiveMutexRecursive( xMutex )
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#endif /* SEMAPHORE_H */
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