This document shows how to use a mutex and semaphores in order to synchronize two tasks in a FreeRTOS and SDK project. For this. This tutorial shows how to use FreeRTOS mutexes to avoid race conditions between different threads. We will show how preemption could. #include “FreeRTOS.h” #include “semphr.h” SemaphoreHandle_t xSemaphoreCreateMutex(void);. Summary. Creates a mutex type semaphore, and returns a.

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Creates a mutex type semaphore, and returns a handle by which the mutex can be referenced.

Each mutex type semaphore requires a small amount of RAM that is used to hold the semaphore’s state. If a mutex is created using xSemaphoreCreateMutexStatic then the RAM is provided by the application writer, which requires an additional parameter, but allows the RAM to be statically allocated at compile time.

Returned if the semaphore cannot be created because there is insufficient heap memory available for FreeRTOS to allocate the semaphore data structures. The semaphore was created successfully. The returned value is a handle by which the created semaphore can be referenced.


FreeRTOS API Reference: Semaphore / Mutexes

Binary semaphores and mutexes are very similar, but do have some subtle differences. Mutexes include a priority inheritance mechanism, binary semaphores do not.

This makes binary semaphores the better choice for implementing synchronization between tasks or between tasks and an interruptand mutexes the better choice for implementing simple mutual exclusion. Binary Semaphores – A binary semaphore used for synchronization does not need to be ‘given’ back after it has been successfully ‘taken’ obtained. Task synchronization is implemented by having one task or interrupt ‘give’ the semaphore, and another task ‘take’ the semaphore see the xSemaphoreGiveFromISR documentation.

Mutexes – The priority of a task that holds a mutex will be raised if another task of higher priority attempts to obtain the same mutex. The task that already holds the mutex is said to ‘inherit’ the priority of the task that is attempting to ‘take’ the same mutex.

freertos queue or mutex – Stack Overflow

The inherited priority will be ‘disinherited’ when the mutex is returned the task that inherited a higher priority while it freertis a mutex will return to its original priority when the mutex is returned. A task that obtains a mutex that is used for mutual exclusion must always give the mutex back – otherwise no other task will ever be able to obtain the same mutex.


An example of a mutex being used to implement mutual exclusion is provided in the xSemaphoreTake section of this manual. Javascript is disabled or is unavailable in your browser. Please refer to your browser’s Help pages for instructions.

Sign In to the Console. Any other value The semaphore was created successfully.

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