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Question/Suggestion for Semaphores

Posted by bodev on November 20, 2008
Hi all,
i am using a semaphore and one task and ISR communicate with that.

In my app, as suggested in FreeRTOS doc, the ISR always give the semaphore and the task always take it. however, the first interaction of the task the semaphore is already given by the creation function and not by the ISR.
This cause not correct exectution.

I noticed that in the creation (vSemaphoreCreateBinary) the semaphore is automatically "given" (xSemaphoreGive).

This problem is easily solvable by "taking" the semaphore just after creation, but it might be a good idea to have a parameter in vSemaphoreCreateBinary in order for the developer to choose if the created semapore should be given or not. or at least document this.

Am i correct? any comments?


RE: Question/Suggestion for Semaphores

Posted by Dave on November 21, 2008
Your suggestion is valid but it would have to be done in a way that was backward compatible. Maybe maintain the original function to create the semaphore and introduce a new function that has the extra parameter.

RE: Question/Suggestion for Semaphores

Posted by saiberion on November 21, 2008
by the way, what is the reason that a semaphore is given on creation?

RE: Question/Suggestion for Semaphores

Posted by Jesper Matthiesen on November 21, 2008
i wondered about that on several occasions as well.. appears more natural that it is initially "taken" i would think...

RE: Question/Suggestion for Semaphores

Posted by Martin Velek on November 23, 2008

I was wondering too, so I replaced classic binary semaphore with counting semaphore

UARTTxBinSemaphore = xSemaphoreCreateCounting( 1, 0 );


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