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*/ | |
#ifndef SEMAPHORE_H | |
#define SEMAPHORE_H | |
#ifndef INC_FREERTOS_H | |
#error "include FreeRTOS.h" must appear in source files before "include semphr.h" | |
#endif | |
#ifdef __cplusplus | |
extern "C" { | |
#endif | |
#include "queue.h" | |
typedef QueueHandle_t SemaphoreHandle_t; | |
#define semBINARY_SEMAPHORE_QUEUE_LENGTH ( ( uint8_t ) 1U ) | |
#define semSEMAPHORE_QUEUE_ITEM_LENGTH ( ( uint8_t ) 0U ) | |
#define semGIVE_BLOCK_TIME ( ( TickType_t ) 0U ) | |
/** | |
* semphr. h | |
* <pre>vSemaphoreCreateBinary( SemaphoreHandle_t xSemaphore )</pre> | |
* | |
* This old vSemaphoreCreateBinary() macro is now deprecated in favour of the | |
* xSemaphoreCreateBinary() function. Note that binary semaphores created using | |
* the vSemaphoreCreateBinary() macro are created in a state such that the | |
* first call to 'take' the semaphore would pass, whereas binary semaphores | |
* created using xSemaphoreCreateBinary() are created in a state such that the | |
* the semaphore must first be 'given' before it can be 'taken'. | |
* | |
* <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 SemaphoreHandle_t. | |
* | |
* Example usage: | |
<pre> | |
SemaphoreHandle_t xSemaphore = NULL; | |
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 ) = xQueueGenericCreate( ( UBaseType_t ) 1, semSEMAPHORE_QUEUE_ITEM_LENGTH, queueQUEUE_TYPE_BINARY_SEMAPHORE ); \ | |
if( ( xSemaphore ) != NULL ) \ | |
{ \ | |
( void ) xSemaphoreGive( ( xSemaphore ) ); \ | |
} \ | |
} | |
*/ | |
/** | |
* semphr. h | |
* <pre>SemaphoreHandle_t xSemaphoreCreateBinary( void )</pre> | |
* | |
* The old vSemaphoreCreateBinary() macro is now deprecated in favour of this | |
* xSemaphoreCreateBinary() function. Note that binary semaphores created using | |
* the vSemaphoreCreateBinary() macro are created in a state such that the | |
* first call to 'take' the semaphore would pass, whereas binary semaphores | |
* created using xSemaphoreCreateBinary() are created in a state such that the | |
* the semaphore must first be 'given' before it can be 'taken'. | |
* | |
* Function that creates 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 nothing is actually stored - all that is important is whether the queue is | |
* empty or full (the binary semaphore is available or not). | |
* | |
* 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(). | |
* | |
* @return Handle to the created semaphore. | |
* | |
* Example usage: | |
<pre> | |
SemaphoreHandle_t xSemaphore = NULL; | |
void vATask( void * pvParameters ) | |
{ | |
// Semaphore cannot be used before a call to vSemaphoreCreateBinary (). | |
// This is a macro so pass the variable in directly. | |
xSemaphore = xSemaphoreCreateBinary(); | |
if( xSemaphore != NULL ) | |
{ | |
// The semaphore was created successfully. | |
// The semaphore can now be used. | |
} | |
} | |
</pre> | |
* \defgroup vSemaphoreCreateBinary vSemaphoreCreateBinary | |
* \ingroup Semaphores | |
*/ | |
#define xSemaphoreCreateBinary() xQueueGenericCreate( NULL, ( UBaseType_t ) 1, semSEMAPHORE_QUEUE_ITEM_LENGTH, queueQUEUE_TYPE_BINARY_SEMAPHORE ) | |
/** | |
* semphr. h | |
* <pre>xSemaphoreTake( | |
* SemaphoreHandle_t xSemaphore, | |
* TickType_t 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_PERIOD_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> | |
SemaphoreHandle_t 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, ( TickType_t ) 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( ( QueueHandle_t ) ( xSemaphore ), NULL, ( xBlockTime ), pdFALSE ) | |
/** | |
* semphr. h | |
* xSemaphoreTakeRecursive( | |
* SemaphoreHandle_t xMutex, | |
* TickType_t 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_PERIOD_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> | |
SemaphoreHandle_t 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, ( TickType_t ) 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, ( TickType_t ) 10 ); | |
xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 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( ( QueueHandle_t ) ( xSemaphore ), NULL, ( xBlockTime ), pdFALSE ) | |
/** | |
* semphr. h | |
* <pre>xSemaphoreGive( SemaphoreHandle_t 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> | |
SemaphoreHandle_t 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, ( TickType_t ) 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( ( QueueHandle_t ) ( xSemaphore ), NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK ) | |
/** | |
* semphr. h | |
* <pre>xSemaphoreGiveRecursive( SemaphoreHandle_t 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> | |
SemaphoreHandle_t 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, ( TickType_t ) 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, ( TickType_t ) 10 ); | |
xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 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( ( QueueHandle_t ) ( xSemaphore ), NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK ) | |
/** | |
* semphr. h | |
* <pre> | |
xSemaphoreGiveFromISR( | |
SemaphoreHandle_t xSemaphore, | |
BaseType_t *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 | |
SemaphoreHandle_t 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 uint8_t ucLocalTickCount = 0; | |
static BaseType_t 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( ( QueueHandle_t ) ( xSemaphore ), NULL, ( pxHigherPriorityTaskWoken ), queueSEND_TO_BACK ) | |
/** | |
* semphr. h | |
* <pre> | |
xSemaphoreTakeFromISR( | |
SemaphoreHandle_t xSemaphore, | |
BaseType_t *pxHigherPriorityTaskWoken | |
)</pre> | |
* | |
* <i>Macro</i> to take a semaphore from an ISR. 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, however taking a semaphore from an ISR | |
* is not a common operation. It is likely to only be useful when taking a | |
* counting semaphore when an interrupt is obtaining an object from a resource | |
* pool (when the semaphore count indicates the number of resources available). | |
* | |
* @param xSemaphore A handle to the semaphore being taken. This is the | |
* handle returned when the semaphore was created. | |
* | |
* @param pxHigherPriorityTaskWoken xSemaphoreTakeFromISR() will set | |
* *pxHigherPriorityTaskWoken to pdTRUE if taking the semaphore caused a task | |
* to unblock, and the unblocked task has a priority higher than the currently | |
* running task. If xSemaphoreTakeFromISR() sets this value to pdTRUE then | |
* a context switch should be requested before the interrupt is exited. | |
* | |
* @return pdTRUE if the semaphore was successfully taken, otherwise | |
* pdFALSE | |
*/ | |
#define xSemaphoreTakeFromISR( xSemaphore, pxHigherPriorityTaskWoken ) xQueueReceiveFromISR( ( QueueHandle_t ) ( xSemaphore ), NULL, ( pxHigherPriorityTaskWoken ) ) | |
/** | |
* semphr. h | |
* <pre>SemaphoreHandle_t 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 | |
* SemaphoreHandle_t. | |
* | |
* Example usage: | |
<pre> | |
SemaphoreHandle_t 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( queueQUEUE_TYPE_MUTEX ) | |
/** | |
* semphr. h | |
* <pre>SemaphoreHandle_t 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 | |
* SemaphoreHandle_t. | |
* | |
* Example usage: | |
<pre> | |
SemaphoreHandle_t 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( queueQUEUE_TYPE_RECURSIVE_MUTEX ) | |
/** | |
* semphr. h | |
* <pre>SemaphoreHandle_t xSemaphoreCreateCounting( UBaseType_t uxMaxCount, UBaseType_t 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> | |
SemaphoreHandle_t xSemaphore; | |
void vATask( void * pvParameters ) | |
{ | |
SemaphoreHandle_t 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 ) ) | |
/** | |
* semphr. h | |
* <pre>void vSemaphoreDelete( SemaphoreHandle_t xSemaphore );</pre> | |
* | |
* Delete a semaphore. This function must be used with care. For example, | |
* do not delete a mutex type semaphore if the mutex is held by a task. | |
* | |
* @param xSemaphore A handle to the semaphore to be deleted. | |
* | |
* \defgroup vSemaphoreDelete vSemaphoreDelete | |
* \ingroup Semaphores | |
*/ | |
#define vSemaphoreDelete( xSemaphore ) vQueueDelete( ( QueueHandle_t ) ( xSemaphore ) ) | |
/** | |
* semphr.h | |
* <pre>TaskHandle_t xSemaphoreGetMutexHolder( SemaphoreHandle_t xMutex );</pre> | |
* | |
* If xMutex is indeed a mutex type semaphore, return the current mutex holder. | |
* If xMutex is not a mutex type semaphore, or the mutex is available (not held | |
* by a task), return NULL. | |
* | |
* Note: This is a good way of determining if the calling task is the mutex | |
* holder, but not a good way of determining the identity of the mutex holder as | |
* the holder may change between the function exiting and the returned value | |
* being tested. | |
*/ | |
#define xSemaphoreGetMutexHolder( xSemaphore ) xQueueGetMutexHolder( ( xSemaphore ) ) | |
#ifdef __cplusplus | |
} | |
#endif | |
#endif /* SEMAPHORE_H */ | |