topic Re: FreeRTOS xSemaphoreTakeFromISR() not blocking in Kinetis Software Development Kit

FreeRTOS xSemaphoreTakeFromISR() not blocking

momirpartalo — Tue, 21 Jun 2016 18:53:32 GMT

I am using FreeRTOS from the Kinetis SDK 1.3.0. A snippet of my code is provided below. Why is the second call to xSemaphoreTakeFromISR() not blocking and not waiting for xSemaphoreGiveFromISR() to release the binary semaphore? If I disable xSemaphoreGiveFromISR() from within IRQHandler_A(), my code within IRQHandler_B() will still move to the next instruction.

void IRQHandler_A(void)

{

…..

xSemaphoreGiveFromISR(Sem, NULL);

…..

}

void IRQHandler_B(void)

{

static bool once = true;

if(once)

{

xSemaphoreTakeFromISR(Sem, NULL); // first time

once = false;

}

…..

xSemaphoreTakeFromISR(Sem, NULL);

// next instruction

…..

}

Re: FreeRTOS xSemaphoreTakeFromISR() not blocking

BlackNight — Wed, 22 Jun 2016 05:22:56 GMT

Hi Momir,

see This page describes the xSemaphoreTakeFromISR() RTOS API function . Taking a semaphore in an interrupt is not (and should not!) block. Blocking in a semaphore would be a very, very bad thing anyway.

If you need to know if the semaphore was available, you can check the return value of xSemaphoreTakeFromISR() (see above lik to the documentation).

I hope this helps,

Erich

Re: FreeRTOS xSemaphoreTakeFromISR() not blocking

xiangjun_rong — Wed, 22 Jun 2016 08:24:21 GMT

Hi, Momir,

From instinct, it seems that xSemaphoreTakeFromISR() should not appear in an interrupt service routine as Erich said, how about creating a task, and put the xSemaphoreTakeFromISR() in a forever loop in the task.

I am not sure if the xSemaphoreTakeFromISR() can appear in an ISR, it is only my opinion, pls refer to the FreeRTOS website:

FreeRTOS - Market leading RTOS (Real Time Operating System) for embedded systems with Internet of Things extensions

Hope it can help you.

XiangJun Rong

Re: FreeRTOS xSemaphoreTakeFromISR() not blocking

BlackNight — Wed, 22 Jun 2016 09:27:29 GMT

FYI, the *FromISR() functions should be called only from an interrupt service routines.

From a task the xSemaphoreTake() API has to be called.

Erich