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Take Semaphore before starting tasks

Posted by chaabanemalki on September 23, 2014

Hello, Since I started using FreeRTOS I had this weird behavior ( or it's normal). I create a semaphore (RxSemaphore), then i use this semaphore to block a task (Task0) with it. And another task (task1) to give RxSemaphore. When I run my code, Task0 takes RxSemaphore even if task1 didn't give RxSemaphore yet. The solution I use is to take RxSemaphore (xSemaphoreTake(RxSemaphore ,0);) in the first task that will run.

Is this a normal behavior or I'm missing something ?


Take Semaphore before starting tasks

Posted by rtel on September 23, 2014

That would depend on which function you were using to create the semaphore.

Regards.


Take Semaphore before starting tasks

Posted by chaabanemalki on September 23, 2014

I use only vSemaphoreCreateBinary(). Thank u


Take Semaphore before starting tasks

Posted by rtel on September 23, 2014

I use only vSemaphoreCreateBinary().

If you look at the vSemaphoreCreateBinary() macro you will see the initial state for the semaphore.

Assuming you are using a recent version of FreeRTOS it is recommended to use xSemaphoreCreateBinary() in place of vSemaphoreCreateBinary(). When using the 'x' function rather than the 'v' macro the semaphore will not be available until it has first been given.

Regards.


Take Semaphore before starting tasks

Posted by chaabanemalki on September 23, 2014

Thank you, that clears everything


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