Semaphore - freeRTOS

mjc — Sun, 10 Apr 2016 14:32:41 GMT

Hi. I'm using freeRTOS on the FRDM KL25Z board. How could I use semaphore to manage 2 tasks? Does anyone have any example?

Re: Semaphore - freeRTOS

BlackNight — Sun, 10 Apr 2016 17:12:49 GMT

Hi Murilo,

not sure what you mean with 'manage 2 tasks' with a semaphore?

Have a look at the API and examples here: FreeRTOS semaphore and mutex API functions vSemaphoreCreateBinary, xSemaphoreCreateCounting, xSemaphoreCreateMutex, xSem…

Other then that: semaphore are used more synchronization, and you can use it either for message passing or for locking/unlocking.

I have here an example of using semaphores for task execution control:

tatic void vSlaveTask(void *pvParameters) {

xSemaphoreHandle sem;

sem = (xSemaphoreHandle)pvParameters;

for(;;) {

if (sem != NULL) {

if (xSemaphoreTake(sem, portMAX_DELAY)==pdTRUE) {

LED1_Neg();

}

static void vMasterTask(void *pvParameters) {

/*! \todo Implement functionality */

xSemaphoreHandle sem = NULL;

(void)pvParameters; /* parameter not used */

sem = xSemaphoreCreateBinary();

if (sem==NULL) { /* semaphore creation failed */

for(;;){} /* error */

}

vQueueAddToRegistry(sem, "IPC_Sem");

/* create slave task */

if (xTaskCreate(vSlaveTask, "Slave", configMINIMAL_STACK_SIZE, sem, tskIDLE_PRIORITY+1, NULL) != pdPASS) {

for(;;){} /* error */

}

for(;;) {

if (sem != NULL) { /* valid semaphore? */

(void)xSemaphoreGive(sem); /* give control to other task */

vTaskDelay(1000/portTICK_PERIOD_MS);

}

I hope this helps,

Erich !

Re: Semaphore - freeRTOS

FreeRTOS_org — Wed, 27 Apr 2016 06:50:42 GMT

If it is only between two tasks then you can also use a direct to task notification.

Re: Semaphore - freeRTOS

mjc — Sun, 15 May 2016 15:13:48 GMT

Hi Erich. Thanks for the help. I was forgetting to put a delay after of "give the semaphore", this way the same task took the semaphore again, and my application was "locked" in a only task.

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