2 FreeRTOS.org V5.1.0 - Copyright (C) 2003-2008 Richard Barry.
\r
4 This file is part of the FreeRTOS.org distribution.
\r
6 FreeRTOS.org is free software; you can redistribute it and/or modify
\r
7 it under the terms of the GNU General Public License as published by
\r
8 the Free Software Foundation; either version 2 of the License, or
\r
9 (at your option) any later version.
\r
11 FreeRTOS.org is distributed in the hope that it will be useful,
\r
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
\r
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
\r
14 GNU General Public License for more details.
\r
16 You should have received a copy of the GNU General Public License
\r
17 along with FreeRTOS.org; if not, write to the Free Software
\r
18 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
\r
20 A special exception to the GPL can be applied should you wish to distribute
\r
21 a combined work that includes FreeRTOS.org, without being obliged to provide
\r
22 the source code for any proprietary components. See the licensing section
\r
23 of http://www.FreeRTOS.org for full details of how and when the exception
\r
26 ***************************************************************************
\r
27 ***************************************************************************
\r
29 * SAVE TIME AND MONEY! We can port FreeRTOS.org to your own hardware, *
\r
30 * and even write all or part of your application on your behalf. *
\r
31 * See http://www.OpenRTOS.com for details of the services we provide to *
\r
32 * expedite your project. *
\r
34 ***************************************************************************
\r
35 ***************************************************************************
\r
37 Please ensure to read the configuration and relevant port sections of the
\r
38 online documentation.
\r
40 http://www.FreeRTOS.org - Documentation, latest information, license and
\r
43 http://www.SafeRTOS.com - A version that is certified for use in safety
\r
46 http://www.OpenRTOS.com - Commercial support, development, porting,
\r
47 licensing and training services.
\r
50 #ifndef INC_FREERTOS_H
\r
51 #error "#include FreeRTOS.h" must appear in source files before "#include semphr.h"
\r
59 typedef xQueueHandle xSemaphoreHandle;
\r
61 #define semBINARY_SEMAPHORE_QUEUE_LENGTH ( ( unsigned portCHAR ) 1 )
\r
62 #define semSEMAPHORE_QUEUE_ITEM_LENGTH ( ( unsigned portCHAR ) 0 )
\r
63 #define semGIVE_BLOCK_TIME ( ( portTickType ) 0 )
\r
68 * <pre>vSemaphoreCreateBinary( xSemaphoreHandle xSemaphore )</pre>
\r
70 * <i>Macro</i> that implements a semaphore by using the existing queue mechanism.
\r
71 * The queue length is 1 as this is a binary semaphore. The data size is 0
\r
72 * as we don't want to actually store any data - we just want to know if the
\r
73 * queue is empty or full.
\r
75 * This type of semaphore can be used for pure synchronisation between tasks or
\r
76 * between an interrupt and a task. The semaphore need not be given back once
\r
77 * obtained, so one task/interrupt can continuously 'give' the semaphore while
\r
78 * another continuously 'takes' the semaphore. For this reason this type of
\r
79 * semaphore does not use a priority inheritance mechanism. For an alternative
\r
80 * that does use priority inheritance see xSemaphoreCreateMutex().
\r
82 * @param xSemaphore Handle to the created semaphore. Should be of type xSemaphoreHandle.
\r
86 xSemaphoreHandle xSemaphore;
\r
88 void vATask( void * pvParameters )
\r
90 // Semaphore cannot be used before a call to vSemaphoreCreateBinary ().
\r
91 // This is a macro so pass the variable in directly.
\r
92 vSemaphoreCreateBinary( xSemaphore );
\r
94 if( xSemaphore != NULL )
\r
96 // The semaphore was created successfully.
\r
97 // The semaphore can now be used.
\r
101 * \defgroup vSemaphoreCreateBinary vSemaphoreCreateBinary
\r
102 * \ingroup Semaphores
\r
104 #define vSemaphoreCreateBinary( xSemaphore ) { \
\r
105 xSemaphore = xQueueCreate( ( unsigned portBASE_TYPE ) 1, semSEMAPHORE_QUEUE_ITEM_LENGTH ); \
\r
106 if( xSemaphore != NULL ) \
\r
108 xSemaphoreGive( xSemaphore ); \
\r
115 * xSemaphoreHandle xSemaphore,
\r
116 * portTickType xBlockTime
\r
119 * <i>Macro</i> to obtain a semaphore. The semaphore must have previously been
\r
120 * created with a call to vSemaphoreCreateBinary(), xSemaphoreCreateMutex() or
\r
121 * xSemaphoreCreateCounting().
\r
123 * @param xSemaphore A handle to the semaphore being taken - obtained when
\r
124 * the semaphore was created.
\r
126 * @param xBlockTime The time in ticks to wait for the semaphore to become
\r
127 * available. The macro portTICK_RATE_MS can be used to convert this to a
\r
128 * real time. A block time of zero can be used to poll the semaphore. A block
\r
129 * time of portMAX_DELAY can be used to block indefinitely (provided
\r
130 * INCLUDE_vTaskSuspend is set to 1 in FreeRTOSConfig.h).
\r
132 * @return pdTRUE if the semaphore was obtained. pdFALSE
\r
133 * if xBlockTime expired without the semaphore becoming available.
\r
137 xSemaphoreHandle xSemaphore = NULL;
\r
139 // A task that creates a semaphore.
\r
140 void vATask( void * pvParameters )
\r
142 // Create the semaphore to guard a shared resource.
\r
143 vSemaphoreCreateBinary( xSemaphore );
\r
146 // A task that uses the semaphore.
\r
147 void vAnotherTask( void * pvParameters )
\r
149 // ... Do other things.
\r
151 if( xSemaphore != NULL )
\r
153 // See if we can obtain the semaphore. If the semaphore is not available
\r
154 // wait 10 ticks to see if it becomes free.
\r
155 if( xSemaphoreTake( xSemaphore, ( portTickType ) 10 ) == pdTRUE )
\r
157 // We were able to obtain the semaphore and can now access the
\r
158 // shared resource.
\r
162 // We have finished accessing the shared resource. Release the
\r
164 xSemaphoreGive( xSemaphore );
\r
168 // We could not obtain the semaphore and can therefore not access
\r
169 // the shared resource safely.
\r
174 * \defgroup xSemaphoreTake xSemaphoreTake
\r
175 * \ingroup Semaphores
\r
177 #define xSemaphoreTake( xSemaphore, xBlockTime ) xQueueGenericReceive( ( xQueueHandle ) xSemaphore, NULL, xBlockTime, pdFALSE )
\r
181 * xSemaphoreTakeRecursive(
\r
182 * xSemaphoreHandle xMutex,
\r
183 * portTickType xBlockTime
\r
186 * <i>Macro</i> to recursively obtain, or 'take', a mutex type semaphore.
\r
187 * The mutex must have previously been created using a call to
\r
188 * xSemaphoreCreateRecursiveMutex();
\r
190 * configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this
\r
191 * macro to be available.
\r
193 * This macro must not be used on mutexes created using xSemaphoreCreateMutex().
\r
195 * A mutex used recursively can be 'taken' repeatedly by the owner. The mutex
\r
196 * doesn't become available again until the owner has called
\r
197 * xSemaphoreGiveRecursive() for each successful 'take' request. For example,
\r
198 * if a task successfully 'takes' the same mutex 5 times then the mutex will
\r
199 * not be available to any other task until it has also 'given' the mutex back
\r
200 * exactly five times.
\r
202 * @param xMutex A handle to the mutex being obtained. This is the
\r
203 * handle returned by xSemaphoreCreateRecursiveMutex();
\r
205 * @param xBlockTime The time in ticks to wait for the semaphore to become
\r
206 * available. The macro portTICK_RATE_MS can be used to convert this to a
\r
207 * real time. A block time of zero can be used to poll the semaphore. If
\r
208 * the task already owns the semaphore then xSemaphoreTakeRecursive() will
\r
209 * return immediately no matter what the value of xBlockTime.
\r
211 * @return pdTRUE if the semaphore was obtained. pdFALSE if xBlockTime
\r
212 * expired without the semaphore becoming available.
\r
216 xSemaphoreHandle xMutex = NULL;
\r
218 // A task that creates a mutex.
\r
219 void vATask( void * pvParameters )
\r
221 // Create the mutex to guard a shared resource.
\r
222 xMutex = xSemaphoreCreateRecursiveMutex();
\r
225 // A task that uses the mutex.
\r
226 void vAnotherTask( void * pvParameters )
\r
228 // ... Do other things.
\r
230 if( xMutex != NULL )
\r
232 // See if we can obtain the mutex. If the mutex is not available
\r
233 // wait 10 ticks to see if it becomes free.
\r
234 if( xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 ) == pdTRUE )
\r
236 // We were able to obtain the mutex and can now access the
\r
237 // shared resource.
\r
240 // For some reason due to the nature of the code further calls to
\r
241 // xSemaphoreTakeRecursive() are made on the same mutex. In real
\r
242 // code these would not be just sequential calls as this would make
\r
243 // no sense. Instead the calls are likely to be buried inside
\r
244 // a more complex call structure.
\r
245 xSemaphoreTakeRecursive( xMutex, ( portTickType ) 10 );
\r
246 xSemaphoreTakeRecursive( xMutex, ( portTickType ) 10 );
\r
248 // The mutex has now been 'taken' three times, so will not be
\r
249 // available to another task until it has also been given back
\r
250 // three times. Again it is unlikely that real code would have
\r
251 // these calls sequentially, but instead buried in a more complex
\r
252 // call structure. This is just for illustrative purposes.
\r
253 xSemaphoreGiveRecursive( xMutex );
\r
254 xSemaphoreGiveRecursive( xMutex );
\r
255 xSemaphoreGiveRecursive( xMutex );
\r
257 // Now the mutex can be taken by other tasks.
\r
261 // We could not obtain the mutex and can therefore not access
\r
262 // the shared resource safely.
\r
267 * \defgroup xSemaphoreTakeRecursive xSemaphoreTakeRecursive
\r
268 * \ingroup Semaphores
\r
270 #define xSemaphoreTakeRecursive( xMutex, xBlockTime ) xQueueTakeMutexRecursive( xMutex, xBlockTime )
\r
274 * xSemaphoreAltTake() is an alternative version of xSemaphoreTake().
\r
276 * The source code that implements the alternative (Alt) API is much
\r
277 * simpler because it executes everything from within a critical section.
\r
278 * This is the approach taken by many other RTOSes, but FreeRTOS.org has the
\r
279 * preferred fully featured API too. The fully featured API has more
\r
280 * complex code that takes longer to execute, but makes much less use of
\r
281 * critical sections. Therefore the alternative API sacrifices interrupt
\r
282 * responsiveness to gain execution speed, whereas the fully featured API
\r
283 * sacrifices execution speed to ensure better interrupt responsiveness.
\r
285 #define xSemaphoreAltTake( xSemaphore, xBlockTime ) xQueueAltGenericReceive( ( xQueueHandle ) xSemaphore, NULL, xBlockTime, pdFALSE )
\r
289 * <pre>xSemaphoreGive( xSemaphoreHandle xSemaphore )</pre>
\r
291 * <i>Macro</i> to release a semaphore. The semaphore must have previously been
\r
292 * created with a call to vSemaphoreCreateBinary(), xSemaphoreCreateMutex() or
\r
293 * xSemaphoreCreateCounting(). and obtained using sSemaphoreTake().
\r
295 * This macro must not be used from an ISR. See xSemaphoreGiveFromISR () for
\r
296 * an alternative which can be used from an ISR.
\r
298 * This macro must also not be used on semaphores created using
\r
299 * xSemaphoreCreateRecursiveMutex().
\r
301 * @param xSemaphore A handle to the semaphore being released. This is the
\r
302 * handle returned when the semaphore was created.
\r
304 * @return pdTRUE if the semaphore was released. pdFALSE if an error occurred.
\r
305 * Semaphores are implemented using queues. An error can occur if there is
\r
306 * no space on the queue to post a message - indicating that the
\r
307 * semaphore was not first obtained correctly.
\r
311 xSemaphoreHandle xSemaphore = NULL;
\r
313 void vATask( void * pvParameters )
\r
315 // Create the semaphore to guard a shared resource.
\r
316 vSemaphoreCreateBinary( xSemaphore );
\r
318 if( xSemaphore != NULL )
\r
320 if( xSemaphoreGive( xSemaphore ) != pdTRUE )
\r
322 // We would expect this call to fail because we cannot give
\r
323 // a semaphore without first "taking" it!
\r
326 // Obtain the semaphore - don't block if the semaphore is not
\r
327 // immediately available.
\r
328 if( xSemaphoreTake( xSemaphore, ( portTickType ) 0 ) )
\r
330 // We now have the semaphore and can access the shared resource.
\r
334 // We have finished accessing the shared resource so can free the
\r
336 if( xSemaphoreGive( xSemaphore ) != pdTRUE )
\r
338 // We would not expect this call to fail because we must have
\r
339 // obtained the semaphore to get here.
\r
345 * \defgroup xSemaphoreGive xSemaphoreGive
\r
346 * \ingroup Semaphores
\r
348 #define xSemaphoreGive( xSemaphore ) xQueueGenericSend( ( xQueueHandle ) xSemaphore, NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK )
\r
352 * <pre>xSemaphoreGiveRecursive( xSemaphoreHandle xMutex )</pre>
\r
354 * <i>Macro</i> to recursively release, or 'give', a mutex type semaphore.
\r
355 * The mutex must have previously been created using a call to
\r
356 * xSemaphoreCreateRecursiveMutex();
\r
358 * configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this
\r
359 * macro to be available.
\r
361 * This macro must not be used on mutexes created using xSemaphoreCreateMutex().
\r
363 * A mutex used recursively can be 'taken' repeatedly by the owner. The mutex
\r
364 * doesn't become available again until the owner has called
\r
365 * xSemaphoreGiveRecursive() for each successful 'take' request. For example,
\r
366 * if a task successfully 'takes' the same mutex 5 times then the mutex will
\r
367 * not be available to any other task until it has also 'given' the mutex back
\r
368 * exactly five times.
\r
370 * @param xMutex A handle to the mutex being released, or 'given'. This is the
\r
371 * handle returned by xSemaphoreCreateMutex();
\r
373 * @return pdTRUE if the semaphore was given.
\r
377 xSemaphoreHandle xMutex = NULL;
\r
379 // A task that creates a mutex.
\r
380 void vATask( void * pvParameters )
\r
382 // Create the mutex to guard a shared resource.
\r
383 xMutex = xSemaphoreCreateRecursiveMutex();
\r
386 // A task that uses the mutex.
\r
387 void vAnotherTask( void * pvParameters )
\r
389 // ... Do other things.
\r
391 if( xMutex != NULL )
\r
393 // See if we can obtain the mutex. If the mutex is not available
\r
394 // wait 10 ticks to see if it becomes free.
\r
395 if( xSemaphoreTakeRecursive( xMutex, ( portTickType ) 10 ) == pdTRUE )
\r
397 // We were able to obtain the mutex and can now access the
\r
398 // shared resource.
\r
401 // For some reason due to the nature of the code further calls to
\r
402 // xSemaphoreTakeRecursive() are made on the same mutex. In real
\r
403 // code these would not be just sequential calls as this would make
\r
404 // no sense. Instead the calls are likely to be buried inside
\r
405 // a more complex call structure.
\r
406 xSemaphoreTakeRecursive( xMutex, ( portTickType ) 10 );
\r
407 xSemaphoreTakeRecursive( xMutex, ( portTickType ) 10 );
\r
409 // The mutex has now been 'taken' three times, so will not be
\r
410 // available to another task until it has also been given back
\r
411 // three times. Again it is unlikely that real code would have
\r
412 // these calls sequentially, it would be more likely that the calls
\r
413 // to xSemaphoreGiveRecursive() would be called as a call stack
\r
414 // unwound. This is just for demonstrative purposes.
\r
415 xSemaphoreGiveRecursive( xMutex );
\r
416 xSemaphoreGiveRecursive( xMutex );
\r
417 xSemaphoreGiveRecursive( xMutex );
\r
419 // Now the mutex can be taken by other tasks.
\r
423 // We could not obtain the mutex and can therefore not access
\r
424 // the shared resource safely.
\r
429 * \defgroup xSemaphoreGiveRecursive xSemaphoreGiveRecursive
\r
430 * \ingroup Semaphores
\r
432 #define xSemaphoreGiveRecursive( xMutex ) xQueueGiveMutexRecursive( xMutex )
\r
435 * xSemaphoreAltGive() is an alternative version of xSemaphoreGive().
\r
437 * The source code that implements the alternative (Alt) API is much
\r
438 * simpler because it executes everything from within a critical section.
\r
439 * This is the approach taken by many other RTOSes, but FreeRTOS.org has the
\r
440 * preferred fully featured API too. The fully featured API has more
\r
441 * complex code that takes longer to execute, but makes much less use of
\r
442 * critical sections. Therefore the alternative API sacrifices interrupt
\r
443 * responsiveness to gain execution speed, whereas the fully featured API
\r
444 * sacrifices execution speed to ensure better interrupt responsiveness.
\r
446 #define xSemaphoreAltGive( xSemaphore ) xQueueAltGenericSend( ( xQueueHandle ) xSemaphore, NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK )
\r
451 xSemaphoreGiveFromISR(
\r
452 xSemaphoreHandle xSemaphore,
\r
453 portBASE_TYPE *pxHigherPriorityTaskWoken
\r
456 * <i>Macro</i> to release a semaphore. The semaphore must have previously been
\r
457 * created with a call to vSemaphoreCreateBinary() or xSemaphoreCreateCounting().
\r
459 * Mutex type semaphores (those created using a call to xSemaphoreCreateMutex())
\r
460 * must not be used with this macro.
\r
462 * This macro can be used from an ISR.
\r
464 * @param xSemaphore A handle to the semaphore being released. This is the
\r
465 * handle returned when the semaphore was created.
\r
467 * @param pxHigherPriorityTaskWoken xSemaphoreGiveFromISR() will set
\r
468 * *pxHigherPriorityTaskWoken to pdTRUE if giving the semaphore caused a task
\r
469 * to unblock, and the unblocked task has a priority higher than the currently
\r
470 * running task. If xSemaphoreGiveFromISR() sets this value to pdTRUE then
\r
471 * a context switch should be requested before the interrupt is exited.
\r
473 * @return pdTRUE if the semaphore was successfully given, otherwise errQUEUE_FULL.
\r
477 #define LONG_TIME 0xffff
\r
478 #define TICKS_TO_WAIT 10
\r
479 xSemaphoreHandle xSemaphore = NULL;
\r
481 // Repetitive task.
\r
482 void vATask( void * pvParameters )
\r
486 // We want this task to run every 10 ticks of a timer. The semaphore
\r
487 // was created before this task was started.
\r
489 // Block waiting for the semaphore to become available.
\r
490 if( xSemaphoreTake( xSemaphore, LONG_TIME ) == pdTRUE )
\r
492 // It is time to execute.
\r
496 // We have finished our task. Return to the top of the loop where
\r
497 // we will block on the semaphore until it is time to execute
\r
498 // again. Note when using the semaphore for synchronisation with an
\r
499 // ISR in this manner there is no need to 'give' the semaphore back.
\r
505 void vTimerISR( void * pvParameters )
\r
507 static unsigned portCHAR ucLocalTickCount = 0;
\r
508 static portBASE_TYPE xHigherPriorityTaskWoken;
\r
510 // A timer tick has occurred.
\r
512 // ... Do other time functions.
\r
514 // Is it time for vATask () to run?
\r
515 xHigherPriorityTaskWoken = pdFALSE;
\r
516 ucLocalTickCount++;
\r
517 if( ucLocalTickCount >= TICKS_TO_WAIT )
\r
519 // Unblock the task by releasing the semaphore.
\r
520 xSemaphoreGiveFromISR( xSemaphore, &xHigherPriorityTaskWoken );
\r
522 // Reset the count so we release the semaphore again in 10 ticks time.
\r
523 ucLocalTickCount = 0;
\r
526 if( xHigherPriorityTaskWoken != pdFALSE )
\r
528 // We can force a context switch here. Context switching from an
\r
529 // ISR uses port specific syntax. Check the demo task for your port
\r
530 // to find the syntax required.
\r
534 * \defgroup xSemaphoreGiveFromISR xSemaphoreGiveFromISR
\r
535 * \ingroup Semaphores
\r
537 #define xSemaphoreGiveFromISR( xSemaphore, pxHigherPriorityTaskWoken ) xQueueGenericSendFromISR( ( xQueueHandle ) xSemaphore, NULL, pxHigherPriorityTaskWoken, queueSEND_TO_BACK )
\r
541 * <pre>xSemaphoreHandle xSemaphoreCreateMutex( void )</pre>
\r
543 * <i>Macro</i> that implements a mutex semaphore by using the existing queue
\r
546 * Mutexes created using this macro can be accessed using the xSemaphoreTake()
\r
547 * and xSemaphoreGive() macros. The xSemaphoreTakeRecursive() and
\r
548 * xSemaphoreGiveRecursive() macros should not be used.
\r
550 * This type of semaphore uses a priority inheritance mechanism so a task
\r
551 * 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the
\r
552 * semaphore it is no longer required.
\r
554 * Mutex type semaphores cannot be used from within interrupt service routines.
\r
556 * See vSemaphoreCreateBinary() for an alternative implementation that can be
\r
557 * used for pure synchronisation (where one task or interrupt always 'gives' the
\r
558 * semaphore and another always 'takes' the semaphore) and from within interrupt
\r
559 * service routines.
\r
561 * @return xSemaphore Handle to the created mutex semaphore. Should be of type
\r
562 * xSemaphoreHandle.
\r
566 xSemaphoreHandle xSemaphore;
\r
568 void vATask( void * pvParameters )
\r
570 // Semaphore cannot be used before a call to xSemaphoreCreateMutex().
\r
571 // This is a macro so pass the variable in directly.
\r
572 xSemaphore = xSemaphoreCreateMutex();
\r
574 if( xSemaphore != NULL )
\r
576 // The semaphore was created successfully.
\r
577 // The semaphore can now be used.
\r
581 * \defgroup vSemaphoreCreateMutex vSemaphoreCreateMutex
\r
582 * \ingroup Semaphores
\r
584 #define xSemaphoreCreateMutex() xQueueCreateMutex()
\r
589 * <pre>xSemaphoreHandle xSemaphoreCreateRecursiveMutex( void )</pre>
\r
591 * <i>Macro</i> that implements a recursive mutex by using the existing queue
\r
594 * Mutexes created using this macro can be accessed using the
\r
595 * xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros. The
\r
596 * xSemaphoreTake() and xSemaphoreGive() macros should not be used.
\r
598 * A mutex used recursively can be 'taken' repeatedly by the owner. The mutex
\r
599 * doesn't become available again until the owner has called
\r
600 * xSemaphoreGiveRecursive() for each successful 'take' request. For example,
\r
601 * if a task successfully 'takes' the same mutex 5 times then the mutex will
\r
602 * not be available to any other task until it has also 'given' the mutex back
\r
603 * exactly five times.
\r
605 * This type of semaphore uses a priority inheritance mechanism so a task
\r
606 * 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the
\r
607 * semaphore it is no longer required.
\r
609 * Mutex type semaphores cannot be used from within interrupt service routines.
\r
611 * See vSemaphoreCreateBinary() for an alternative implementation that can be
\r
612 * used for pure synchronisation (where one task or interrupt always 'gives' the
\r
613 * semaphore and another always 'takes' the semaphore) and from within interrupt
\r
614 * service routines.
\r
616 * @return xSemaphore Handle to the created mutex semaphore. Should be of type
\r
617 * xSemaphoreHandle.
\r
621 xSemaphoreHandle xSemaphore;
\r
623 void vATask( void * pvParameters )
\r
625 // Semaphore cannot be used before a call to xSemaphoreCreateMutex().
\r
626 // This is a macro so pass the variable in directly.
\r
627 xSemaphore = xSemaphoreCreateRecursiveMutex();
\r
629 if( xSemaphore != NULL )
\r
631 // The semaphore was created successfully.
\r
632 // The semaphore can now be used.
\r
636 * \defgroup vSemaphoreCreateMutex vSemaphoreCreateMutex
\r
637 * \ingroup Semaphores
\r
639 #define xSemaphoreCreateRecursiveMutex() xQueueCreateMutex()
\r
643 * <pre>xSemaphoreHandle xSemaphoreCreateCounting( unsigned portBASE_TYPE uxMaxCount, unsigned portBASE_TYPE uxInitialCount )</pre>
\r
645 * <i>Macro</i> that creates a counting semaphore by using the existing
\r
646 * queue mechanism.
\r
648 * Counting semaphores are typically used for two things:
\r
650 * 1) Counting events.
\r
652 * In this usage scenario an event handler will 'give' a semaphore each time
\r
653 * an event occurs (incrementing the semaphore count value), and a handler
\r
654 * task will 'take' a semaphore each time it processes an event
\r
655 * (decrementing the semaphore count value). The count value is therefore
\r
656 * the difference between the number of events that have occurred and the
\r
657 * number that have been processed. In this case it is desirable for the
\r
658 * initial count value to be zero.
\r
660 * 2) Resource management.
\r
662 * In this usage scenario the count value indicates the number of resources
\r
663 * available. To obtain control of a resource a task must first obtain a
\r
664 * semaphore - decrementing the semaphore count value. When the count value
\r
665 * reaches zero there are no free resources. When a task finishes with the
\r
666 * resource it 'gives' the semaphore back - incrementing the semaphore count
\r
667 * value. In this case it is desirable for the initial count value to be
\r
668 * equal to the maximum count value, indicating that all resources are free.
\r
670 * @param uxMaxCount The maximum count value that can be reached. When the
\r
671 * semaphore reaches this value it can no longer be 'given'.
\r
673 * @param uxInitialCount The count value assigned to the semaphore when it is
\r
676 * @return Handle to the created semaphore. Null if the semaphore could not be
\r
681 xSemaphoreHandle xSemaphore;
\r
683 void vATask( void * pvParameters )
\r
685 xSemaphoreHandle xSemaphore = NULL;
\r
687 // Semaphore cannot be used before a call to xSemaphoreCreateCounting().
\r
688 // The max value to which the semaphore can count should be 10, and the
\r
689 // initial value assigned to the count should be 0.
\r
690 xSemaphore = xSemaphoreCreateCounting( 10, 0 );
\r
692 if( xSemaphore != NULL )
\r
694 // The semaphore was created successfully.
\r
695 // The semaphore can now be used.
\r
699 * \defgroup xSemaphoreCreateCounting xSemaphoreCreateCounting
\r
700 * \ingroup Semaphores
\r
702 #define xSemaphoreCreateCounting( uxMaxCount, uxInitialCount ) xQueueCreateCountingSemaphore( uxMaxCount, uxInitialCount )
\r
705 #endif /* SEMAPHORE_H */
\r