Question/Suggestion for Semaphores

bodev wrote on Thursday, 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?


davedoors wrote on Friday, 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.

saiberion wrote on Friday, November 21, 2008:

by the way, what is the reason that a semaphore is given on creation?

hooverphonique wrote on Friday, November 21, 2008:

i wondered about that on several occasions as well… appears more natural that it is initially "taken" i would think…

wella wrote on Sunday, November 23, 2008:


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

UARTTxBinSemaphore = xSemaphoreCreateCounting( 1, 0 );