blob: 8977acadb92c61f2bacfc9a0c786f658b35521fa [file] [log] [blame]
/*
* FreeRTOS Kernel <DEVELOPMENT BRANCH>
* Copyright (C) 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* SPDX-License-Identifier: MIT
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
* the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
* https://www.FreeRTOS.org
* https://github.com/FreeRTOS
*
*/
#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
* @code{c}
* vSemaphoreCreateBinary( SemaphoreHandle_t xSemaphore );
* @endcode
*
* In many usage scenarios it is faster and more memory efficient to use a
* direct to task notification in place of a binary semaphore!
* https://www.FreeRTOS.org/RTOS-task-notifications.html
*
* 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:
* @code{c}
* 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.
* }
* }
* @endcode
* \defgroup vSemaphoreCreateBinary vSemaphoreCreateBinary
* \ingroup Semaphores
*/
#if ( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
#define vSemaphoreCreateBinary( xSemaphore ) \
do { \
( xSemaphore ) = xQueueGenericCreate( ( UBaseType_t ) 1, semSEMAPHORE_QUEUE_ITEM_LENGTH, queueQUEUE_TYPE_BINARY_SEMAPHORE ); \
if( ( xSemaphore ) != NULL ) \
{ \
( void ) xSemaphoreGive( ( xSemaphore ) ); \
} \
} while( 0 )
#endif
/**
* semphr. h
* @code{c}
* SemaphoreHandle_t xSemaphoreCreateBinary( void );
* @endcode
*
* Creates a new binary semaphore instance, and returns a handle by which the
* new semaphore can be referenced.
*
* In many usage scenarios it is faster and more memory efficient to use a
* direct to task notification in place of a binary semaphore!
* https://www.FreeRTOS.org/RTOS-task-notifications.html
*
* Internally, within the FreeRTOS implementation, binary semaphores use a block
* of memory, in which the semaphore structure is stored. If a binary semaphore
* is created using xSemaphoreCreateBinary() then the required memory is
* automatically dynamically allocated inside the xSemaphoreCreateBinary()
* function. (see https://www.FreeRTOS.org/a00111.html). If a binary semaphore
* is created using xSemaphoreCreateBinaryStatic() then the application writer
* must provide the memory. xSemaphoreCreateBinaryStatic() therefore allows a
* binary semaphore to be created without using any dynamic memory allocation.
*
* 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'.
*
* 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, or NULL if the memory required to
* hold the semaphore's data structures could not be allocated.
*
* Example usage:
* @code{c}
* SemaphoreHandle_t xSemaphore = NULL;
*
* void vATask( void * pvParameters )
* {
* // Semaphore cannot be used before a call to xSemaphoreCreateBinary().
* // 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.
* }
* }
* @endcode
* \defgroup xSemaphoreCreateBinary xSemaphoreCreateBinary
* \ingroup Semaphores
*/
#if ( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
#define xSemaphoreCreateBinary() xQueueGenericCreate( ( UBaseType_t ) 1, semSEMAPHORE_QUEUE_ITEM_LENGTH, queueQUEUE_TYPE_BINARY_SEMAPHORE )
#endif
/**
* semphr. h
* @code{c}
* SemaphoreHandle_t xSemaphoreCreateBinaryStatic( StaticSemaphore_t *pxSemaphoreBuffer );
* @endcode
*
* Creates a new binary semaphore instance, and returns a handle by which the
* new semaphore can be referenced.
*
* NOTE: In many usage scenarios it is faster and more memory efficient to use a
* direct to task notification in place of a binary semaphore!
* https://www.FreeRTOS.org/RTOS-task-notifications.html
*
* Internally, within the FreeRTOS implementation, binary semaphores use a block
* of memory, in which the semaphore structure is stored. If a binary semaphore
* is created using xSemaphoreCreateBinary() then the required memory is
* automatically dynamically allocated inside the xSemaphoreCreateBinary()
* function. (see https://www.FreeRTOS.org/a00111.html). If a binary semaphore
* is created using xSemaphoreCreateBinaryStatic() then the application writer
* must provide the memory. xSemaphoreCreateBinaryStatic() therefore allows a
* binary semaphore to be created without using any dynamic memory allocation.
*
* 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 pxSemaphoreBuffer Must point to a variable of type StaticSemaphore_t,
* which will then be used to hold the semaphore's data structure, removing the
* need for the memory to be allocated dynamically.
*
* @return If the semaphore is created then a handle to the created semaphore is
* returned. If pxSemaphoreBuffer is NULL then NULL is returned.
*
* Example usage:
* @code{c}
* SemaphoreHandle_t xSemaphore = NULL;
* StaticSemaphore_t xSemaphoreBuffer;
*
* void vATask( void * pvParameters )
* {
* // Semaphore cannot be used before a call to xSemaphoreCreateBinary().
* // The semaphore's data structures will be placed in the xSemaphoreBuffer
* // variable, the address of which is passed into the function. The
* // function's parameter is not NULL, so the function will not attempt any
* // dynamic memory allocation, and therefore the function will not return
* // return NULL.
* xSemaphore = xSemaphoreCreateBinary( &xSemaphoreBuffer );
*
* // Rest of task code goes here.
* }
* @endcode
* \defgroup xSemaphoreCreateBinaryStatic xSemaphoreCreateBinaryStatic
* \ingroup Semaphores
*/
#if ( configSUPPORT_STATIC_ALLOCATION == 1 )
#define xSemaphoreCreateBinaryStatic( pxStaticSemaphore ) xQueueGenericCreateStatic( ( UBaseType_t ) 1, semSEMAPHORE_QUEUE_ITEM_LENGTH, NULL, ( pxStaticSemaphore ), queueQUEUE_TYPE_BINARY_SEMAPHORE )
#endif /* configSUPPORT_STATIC_ALLOCATION */
/**
* semphr. h
* @code{c}
* xSemaphoreTake(
* SemaphoreHandle_t xSemaphore,
* TickType_t xBlockTime
* );
* @endcode
*
* <i>Macro</i> to obtain a semaphore. The semaphore must have previously been
* created with a call to xSemaphoreCreateBinary(), 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:
* @code{c}
* SemaphoreHandle_t xSemaphore = NULL;
*
* // A task that creates a semaphore.
* void vATask( void * pvParameters )
* {
* // Create the semaphore to guard a shared resource.
* xSemaphore = xSemaphoreCreateBinary();
* }
*
* // 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.
* }
* }
* }
* @endcode
* \defgroup xSemaphoreTake xSemaphoreTake
* \ingroup Semaphores
*/
#define xSemaphoreTake( xSemaphore, xBlockTime ) xQueueSemaphoreTake( ( xSemaphore ), ( xBlockTime ) )
/**
* semphr. h
* @code{c}
* xSemaphoreTakeRecursive(
* SemaphoreHandle_t xMutex,
* TickType_t xBlockTime
* );
* @endcode
*
* <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:
* @code{c}
* 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.
* }
* }
* }
* @endcode
* \defgroup xSemaphoreTakeRecursive xSemaphoreTakeRecursive
* \ingroup Semaphores
*/
#if ( configUSE_RECURSIVE_MUTEXES == 1 )
#define xSemaphoreTakeRecursive( xMutex, xBlockTime ) xQueueTakeMutexRecursive( ( xMutex ), ( xBlockTime ) )
#endif
/**
* semphr. h
* @code{c}
* xSemaphoreGive( SemaphoreHandle_t xSemaphore );
* @endcode
*
* <i>Macro</i> to release a semaphore. The semaphore must have previously been
* created with a call to xSemaphoreCreateBinary(), 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:
* @code{c}
* SemaphoreHandle_t xSemaphore = NULL;
*
* void vATask( void * pvParameters )
* {
* // Create the semaphore to guard a shared resource.
* xSemaphore = vSemaphoreCreateBinary();
*
* 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.
* }
* }
* }
* }
* @endcode
* \defgroup xSemaphoreGive xSemaphoreGive
* \ingroup Semaphores
*/
#define xSemaphoreGive( xSemaphore ) xQueueGenericSend( ( QueueHandle_t ) ( xSemaphore ), NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK )
/**
* semphr. h
* @code{c}
* xSemaphoreGiveRecursive( SemaphoreHandle_t xMutex );
* @endcode
*
* <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:
* @code{c}
* 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.
* }
* }
* }
* @endcode
* \defgroup xSemaphoreGiveRecursive xSemaphoreGiveRecursive
* \ingroup Semaphores
*/
#if ( configUSE_RECURSIVE_MUTEXES == 1 )
#define xSemaphoreGiveRecursive( xMutex ) xQueueGiveMutexRecursive( ( xMutex ) )
#endif
/**
* semphr. h
* @code{c}
* xSemaphoreGiveFromISR(
* SemaphoreHandle_t xSemaphore,
* BaseType_t *pxHigherPriorityTaskWoken
* );
* @endcode
*
* <i>Macro</i> to release a semaphore. The semaphore must have previously been
* created with a call to xSemaphoreCreateBinary() 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:
* @code{c}
\#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.
* }
* }
* @endcode
* \defgroup xSemaphoreGiveFromISR xSemaphoreGiveFromISR
* \ingroup Semaphores
*/
#define xSemaphoreGiveFromISR( xSemaphore, pxHigherPriorityTaskWoken ) xQueueGiveFromISR( ( QueueHandle_t ) ( xSemaphore ), ( pxHigherPriorityTaskWoken ) )
/**
* semphr. h
* @code{c}
* xSemaphoreTakeFromISR(
* SemaphoreHandle_t xSemaphore,
* BaseType_t *pxHigherPriorityTaskWoken
* );
* @endcode
*
* <i>Macro</i> to take a semaphore from an ISR. The semaphore must have
* previously been created with a call to xSemaphoreCreateBinary() 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
* @code{c}
* SemaphoreHandle_t xSemaphoreCreateMutex( void );
* @endcode
*
* Creates a new mutex type semaphore instance, and returns a handle by which
* the new mutex can be referenced.
*
* Internally, within the FreeRTOS implementation, mutex semaphores use a block
* of memory, in which the mutex structure is stored. If a mutex is created
* using xSemaphoreCreateMutex() then the required memory is automatically
* dynamically allocated inside the xSemaphoreCreateMutex() function. (see
* https://www.FreeRTOS.org/a00111.html). If a mutex is created using
* xSemaphoreCreateMutexStatic() then the application writer must provided the
* memory. xSemaphoreCreateMutexStatic() therefore allows a mutex to be created
* without using any dynamic memory allocation.
*
* Mutexes created using this function can be accessed using the xSemaphoreTake()
* and xSemaphoreGive() macros. The xSemaphoreTakeRecursive() and
* xSemaphoreGiveRecursive() macros must 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 xSemaphoreCreateBinary() 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 If the mutex was successfully created then a handle to the created
* semaphore is returned. If there was not enough heap to allocate the mutex
* data structures then NULL is returned.
*
* Example usage:
* @code{c}
* 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.
* }
* }
* @endcode
* \defgroup xSemaphoreCreateMutex xSemaphoreCreateMutex
* \ingroup Semaphores
*/
#if ( ( configSUPPORT_DYNAMIC_ALLOCATION == 1 ) && ( configUSE_MUTEXES == 1 ) )
#define xSemaphoreCreateMutex() xQueueCreateMutex( queueQUEUE_TYPE_MUTEX )
#endif
/**
* semphr. h
* @code{c}
* SemaphoreHandle_t xSemaphoreCreateMutexStatic( StaticSemaphore_t *pxMutexBuffer );
* @endcode
*
* Creates a new mutex type semaphore instance, and returns a handle by which
* the new mutex can be referenced.
*
* Internally, within the FreeRTOS implementation, mutex semaphores use a block
* of memory, in which the mutex structure is stored. If a mutex is created
* using xSemaphoreCreateMutex() then the required memory is automatically
* dynamically allocated inside the xSemaphoreCreateMutex() function. (see
* https://www.FreeRTOS.org/a00111.html). If a mutex is created using
* xSemaphoreCreateMutexStatic() then the application writer must provided the
* memory. xSemaphoreCreateMutexStatic() therefore allows a mutex to be created
* without using any dynamic memory allocation.
*
* Mutexes created using this function can be accessed using the xSemaphoreTake()
* and xSemaphoreGive() macros. The xSemaphoreTakeRecursive() and
* xSemaphoreGiveRecursive() macros must 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 xSemaphoreCreateBinary() 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.
*
* @param pxMutexBuffer Must point to a variable of type StaticSemaphore_t,
* which will be used to hold the mutex's data structure, removing the need for
* the memory to be allocated dynamically.
*
* @return If the mutex was successfully created then a handle to the created
* mutex is returned. If pxMutexBuffer was NULL then NULL is returned.
*
* Example usage:
* @code{c}
* SemaphoreHandle_t xSemaphore;
* StaticSemaphore_t xMutexBuffer;
*
* void vATask( void * pvParameters )
* {
* // A mutex cannot be used before it has been created. xMutexBuffer is
* // into xSemaphoreCreateMutexStatic() so no dynamic memory allocation is
* // attempted.
* xSemaphore = xSemaphoreCreateMutexStatic( &xMutexBuffer );
*
* // As no dynamic memory allocation was performed, xSemaphore cannot be NULL,
* // so there is no need to check it.
* }
* @endcode
* \defgroup xSemaphoreCreateMutexStatic xSemaphoreCreateMutexStatic
* \ingroup Semaphores
*/
#if ( ( configSUPPORT_STATIC_ALLOCATION == 1 ) && ( configUSE_MUTEXES == 1 ) )
#define xSemaphoreCreateMutexStatic( pxMutexBuffer ) xQueueCreateMutexStatic( queueQUEUE_TYPE_MUTEX, ( pxMutexBuffer ) )
#endif
/**
* semphr. h
* @code{c}
* SemaphoreHandle_t xSemaphoreCreateRecursiveMutex( void );
* @endcode
*
* Creates a new recursive mutex type semaphore instance, and returns a handle
* by which the new recursive mutex can be referenced.
*
* Internally, within the FreeRTOS implementation, recursive mutexes use a block
* of memory, in which the mutex structure is stored. If a recursive mutex is
* created using xSemaphoreCreateRecursiveMutex() then the required memory is
* automatically dynamically allocated inside the
* xSemaphoreCreateRecursiveMutex() function. (see
* https://www.FreeRTOS.org/a00111.html). If a recursive mutex is created using
* xSemaphoreCreateRecursiveMutexStatic() then the application writer must
* provide the memory that will get used by the mutex.
* xSemaphoreCreateRecursiveMutexStatic() therefore allows a recursive mutex to
* be created without using any dynamic memory allocation.
*
* Mutexes created using this macro can be accessed using the
* xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros. The
* xSemaphoreTake() and xSemaphoreGive() macros must 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 xSemaphoreCreateBinary() 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:
* @code{c}
* 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.
* }
* }
* @endcode
* \defgroup xSemaphoreCreateRecursiveMutex xSemaphoreCreateRecursiveMutex
* \ingroup Semaphores
*/
#if ( ( configSUPPORT_DYNAMIC_ALLOCATION == 1 ) && ( configUSE_RECURSIVE_MUTEXES == 1 ) )
#define xSemaphoreCreateRecursiveMutex() xQueueCreateMutex( queueQUEUE_TYPE_RECURSIVE_MUTEX )
#endif
/**
* semphr. h
* @code{c}
* SemaphoreHandle_t xSemaphoreCreateRecursiveMutexStatic( StaticSemaphore_t *pxMutexBuffer );
* @endcode
*
* Creates a new recursive mutex type semaphore instance, and returns a handle
* by which the new recursive mutex can be referenced.
*
* Internally, within the FreeRTOS implementation, recursive mutexes use a block
* of memory, in which the mutex structure is stored. If a recursive mutex is
* created using xSemaphoreCreateRecursiveMutex() then the required memory is
* automatically dynamically allocated inside the
* xSemaphoreCreateRecursiveMutex() function. (see
* https://www.FreeRTOS.org/a00111.html). If a recursive mutex is created using
* xSemaphoreCreateRecursiveMutexStatic() then the application writer must
* provide the memory that will get used by the mutex.
* xSemaphoreCreateRecursiveMutexStatic() therefore allows a recursive mutex to
* be created without using any dynamic memory allocation.
*
* Mutexes created using this macro can be accessed using the
* xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros. The
* xSemaphoreTake() and xSemaphoreGive() macros must 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 xSemaphoreCreateBinary() 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.
*
* @param pxMutexBuffer Must point to a variable of type StaticSemaphore_t,
* which will then be used to hold the recursive mutex's data structure,
* removing the need for the memory to be allocated dynamically.
*
* @return If the recursive mutex was successfully created then a handle to the
* created recursive mutex is returned. If pxMutexBuffer was NULL then NULL is
* returned.
*
* Example usage:
* @code{c}
* SemaphoreHandle_t xSemaphore;
* StaticSemaphore_t xMutexBuffer;
*
* void vATask( void * pvParameters )
* {
* // A recursive semaphore cannot be used before it is created. Here a
* // recursive mutex is created using xSemaphoreCreateRecursiveMutexStatic().
* // The address of xMutexBuffer is passed into the function, and will hold
* // the mutexes data structures - so no dynamic memory allocation will be
* // attempted.
* xSemaphore = xSemaphoreCreateRecursiveMutexStatic( &xMutexBuffer );
*
* // As no dynamic memory allocation was performed, xSemaphore cannot be NULL,
* // so there is no need to check it.
* }
* @endcode
* \defgroup xSemaphoreCreateRecursiveMutexStatic xSemaphoreCreateRecursiveMutexStatic
* \ingroup Semaphores
*/
#if ( ( configSUPPORT_STATIC_ALLOCATION == 1 ) && ( configUSE_RECURSIVE_MUTEXES == 1 ) )
#define xSemaphoreCreateRecursiveMutexStatic( pxStaticSemaphore ) xQueueCreateMutexStatic( queueQUEUE_TYPE_RECURSIVE_MUTEX, ( pxStaticSemaphore ) )
#endif /* configSUPPORT_STATIC_ALLOCATION */
/**
* semphr. h
* @code{c}
* SemaphoreHandle_t xSemaphoreCreateCounting( UBaseType_t uxMaxCount, UBaseType_t uxInitialCount );
* @endcode
*
* Creates a new counting semaphore instance, and returns a handle by which the
* new counting semaphore can be referenced.
*
* In many usage scenarios it is faster and more memory efficient to use a
* direct to task notification in place of a counting semaphore!
* https://www.FreeRTOS.org/RTOS-task-notifications.html
*
* Internally, within the FreeRTOS implementation, counting semaphores use a
* block of memory, in which the counting semaphore structure is stored. If a
* counting semaphore is created using xSemaphoreCreateCounting() then the
* required memory is automatically dynamically allocated inside the
* xSemaphoreCreateCounting() function. (see
* https://www.FreeRTOS.org/a00111.html). If a counting semaphore is created
* using xSemaphoreCreateCountingStatic() then the application writer can
* instead optionally provide the memory that will get used by the counting
* semaphore. xSemaphoreCreateCountingStatic() therefore allows a counting
* semaphore to be created without using any dynamic memory allocation.
*
* 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:
* @code{c}
* 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.
* }
* }
* @endcode
* \defgroup xSemaphoreCreateCounting xSemaphoreCreateCounting
* \ingroup Semaphores
*/
#if ( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
#define xSemaphoreCreateCounting( uxMaxCount, uxInitialCount ) xQueueCreateCountingSemaphore( ( uxMaxCount ), ( uxInitialCount ) )
#endif
/**
* semphr. h
* @code{c}
* SemaphoreHandle_t xSemaphoreCreateCountingStatic( UBaseType_t uxMaxCount, UBaseType_t uxInitialCount, StaticSemaphore_t *pxSemaphoreBuffer );
* @endcode
*
* Creates a new counting semaphore instance, and returns a handle by which the
* new counting semaphore can be referenced.
*
* In many usage scenarios it is faster and more memory efficient to use a
* direct to task notification in place of a counting semaphore!
* https://www.FreeRTOS.org/RTOS-task-notifications.html
*
* Internally, within the FreeRTOS implementation, counting semaphores use a
* block of memory, in which the counting semaphore structure is stored. If a
* counting semaphore is created using xSemaphoreCreateCounting() then the
* required memory is automatically dynamically allocated inside the
* xSemaphoreCreateCounting() function. (see
* https://www.FreeRTOS.org/a00111.html). If a counting semaphore is created
* using xSemaphoreCreateCountingStatic() then the application writer must
* provide the memory. xSemaphoreCreateCountingStatic() therefore allows a
* counting semaphore to be created without using any dynamic memory allocation.
*
* 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.
*
* @param pxSemaphoreBuffer Must point to a variable of type StaticSemaphore_t,
* which will then be used to hold the semaphore's data structure, removing the
* need for the memory to be allocated dynamically.
*
* @return If the counting semaphore was successfully created then a handle to
* the created counting semaphore is returned. If pxSemaphoreBuffer was NULL
* then NULL is returned.
*
* Example usage:
* @code{c}
* SemaphoreHandle_t xSemaphore;
* StaticSemaphore_t xSemaphoreBuffer;
*
* void vATask( void * pvParameters )
* {
* SemaphoreHandle_t xSemaphore = NULL;
*
* // Counting semaphore cannot be used before they have been created. Create
* // a counting semaphore using xSemaphoreCreateCountingStatic(). The max
* // value to which the semaphore can count is 10, and the initial value
* // assigned to the count will be 0. The address of xSemaphoreBuffer is
* // passed in and will be used to hold the semaphore structure, so no dynamic
* // memory allocation will be used.
* xSemaphore = xSemaphoreCreateCounting( 10, 0, &xSemaphoreBuffer );
*
* // No memory allocation was attempted so xSemaphore cannot be NULL, so there
* // is no need to check its value.
* }
* @endcode
* \defgroup xSemaphoreCreateCountingStatic xSemaphoreCreateCountingStatic
* \ingroup Semaphores
*/
#if ( configSUPPORT_STATIC_ALLOCATION == 1 )
#define xSemaphoreCreateCountingStatic( uxMaxCount, uxInitialCount, pxSemaphoreBuffer ) xQueueCreateCountingSemaphoreStatic( ( uxMaxCount ), ( uxInitialCount ), ( pxSemaphoreBuffer ) )
#endif /* configSUPPORT_STATIC_ALLOCATION */
/**
* semphr. h
* @code{c}
* void vSemaphoreDelete( SemaphoreHandle_t xSemaphore );
* @endcode
*
* 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
* @code{c}
* TaskHandle_t xSemaphoreGetMutexHolder( SemaphoreHandle_t xMutex );
* @endcode
*
* 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.
*/
#if ( ( configUSE_MUTEXES == 1 ) && ( INCLUDE_xSemaphoreGetMutexHolder == 1 ) )
#define xSemaphoreGetMutexHolder( xSemaphore ) xQueueGetMutexHolder( ( xSemaphore ) )
#endif
/**
* semphr.h
* @code{c}
* TaskHandle_t xSemaphoreGetMutexHolderFromISR( SemaphoreHandle_t xMutex );
* @endcode
*
* 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.
*
*/
#if ( ( configUSE_MUTEXES == 1 ) && ( INCLUDE_xSemaphoreGetMutexHolder == 1 ) )
#define xSemaphoreGetMutexHolderFromISR( xSemaphore ) xQueueGetMutexHolderFromISR( ( xSemaphore ) )
#endif
/**
* semphr.h
* @code{c}
* UBaseType_t uxSemaphoreGetCount( SemaphoreHandle_t xSemaphore );
* @endcode
*
* If the semaphore is a counting semaphore then uxSemaphoreGetCount() returns
* its current count value. If the semaphore is a binary semaphore then
* uxSemaphoreGetCount() returns 1 if the semaphore is available, and 0 if the
* semaphore is not available.
*
*/
#define uxSemaphoreGetCount( xSemaphore ) uxQueueMessagesWaiting( ( QueueHandle_t ) ( xSemaphore ) )
/**
* semphr.h
* @code{c}
* UBaseType_t uxSemaphoreGetCountFromISR( SemaphoreHandle_t xSemaphore );
* @endcode
*
* If the semaphore is a counting semaphore then uxSemaphoreGetCountFromISR() returns
* its current count value. If the semaphore is a binary semaphore then
* uxSemaphoreGetCountFromISR() returns 1 if the semaphore is available, and 0 if the
* semaphore is not available.
*
*/
#define uxSemaphoreGetCountFromISR( xSemaphore ) uxQueueMessagesWaitingFromISR( ( QueueHandle_t ) ( xSemaphore ) )
/**
* semphr.h
* @code{c}
* BaseType_t xSemaphoreGetStaticBuffer( SemaphoreHandle_t xSemaphore,
* StaticSemaphore_t ** ppxSemaphoreBuffer );
* @endcode
*
* Retrieve pointer to a statically created binary semaphore, counting semaphore,
* or mutex semaphore's data structure buffer. This is the same buffer that is
* supplied at the time of creation.
*
* @param xSemaphore The semaphore for which to retrieve the buffer.
*
* @param ppxSemaphoreBuffer Used to return a pointer to the semaphore's
* data structure buffer.
*
* @return pdTRUE if buffer was retrieved, pdFALSE otherwise.
*/
#if ( configSUPPORT_STATIC_ALLOCATION == 1 )
#define xSemaphoreGetStaticBuffer( xSemaphore, ppxSemaphoreBuffer ) xQueueGenericGetStaticBuffers( ( QueueHandle_t ) ( xSemaphore ), NULL, ( ppxSemaphoreBuffer ) )
#endif /* configSUPPORT_STATIC_ALLOCATION */
#endif /* SEMAPHORE_H */