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diff --git a/freertos/Source/include/semphr.h b/freertos/Source/include/semphr.h new file mode 100644 index 0000000..9f76072 --- /dev/null +++ b/freertos/Source/include/semphr.h @@ -0,0 +1,844 @@ +/* + FreeRTOS V8.2.3 - Copyright (C) 2015 Real Time Engineers Ltd. + All rights reserved + + VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION. + + 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 modification 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. Full license text is available on the following + link: http://www.freertos.org/a00114.html + + *************************************************************************** + * * + * FreeRTOS provides completely free yet professionally developed, * + * robust, strictly quality controlled, supported, and cross * + * platform software that is more than just the market leader, it * + * is the industry's de facto standard. * + * * + * Help yourself get started quickly while simultaneously helping * + * to support the FreeRTOS project by purchasing a FreeRTOS * + * tutorial book, reference manual, or both: * + * http://www.FreeRTOS.org/Documentation * + * * + *************************************************************************** + + http://www.FreeRTOS.org/FAQHelp.html - Having a problem? Start by reading + the FAQ page "My application does not run, what could be wrong?". Have you + defined configASSERT()? + + http://www.FreeRTOS.org/support - In return for receiving this top quality + embedded software for free we request you assist our global community by + participating in the support forum. + + http://www.FreeRTOS.org/training - Investing in training allows your team to + be as productive as possible as early as possible. Now you can receive + FreeRTOS training directly from Richard Barry, CEO of Real Time Engineers + Ltd, and the world's leading authority on the world's leading RTOS. + + http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products, + including FreeRTOS+Trace - an indispensable productivity tool, a DOS + compatible FAT file system, and our tiny thread aware UDP/IP stack. + + http://www.FreeRTOS.org/labs - Where new FreeRTOS products go to incubate. + Come and try FreeRTOS+TCP, our new open source TCP/IP stack for FreeRTOS. + + http://www.OpenRTOS.com - Real Time Engineers ltd. license FreeRTOS to High + Integrity Systems ltd. to sell under the OpenRTOS brand. Low cost OpenRTOS + licenses offer ticketed support, indemnification and commercial middleware. + + http://www.SafeRTOS.com - High Integrity Systems also provide a safety + engineered and independently SIL3 certified version for use in safety and + mission critical applications that require provable dependability. + + 1 tab == 4 spaces! +*/ + +#ifndef SEMAPHORE_H +#define SEMAPHORE_H + +#ifndef INC_FREERTOS_H + #error "include FreeRTOS.h" must appear in source files before "include semphr.h" +#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( ( 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 + * is not 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() + * returns 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 is not + // 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 is + * not 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 is not + // 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() sets + * *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 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 ) xQueueGiveFromISR( ( QueueHandle_t ) ( xSemaphore ), ( pxHigherPriorityTaskWoken ) ) + +/** + * 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() 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 is + * not 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 'gives' a semaphore each time + * an event occurs (incrementing the semaphore count value), and a handler + * task 'takes' 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 ) ) + +#endif /* SEMAPHORE_H */ + + |