First, the semaphore needs to be created, and its handle (or pointer) has to be stored so that it can be used between tasks. The following excerpt has been taken from mainSemExample.c:

//create storage for a pointer to a semaphore
SemaphoreHandle_t semPtr = NULL;

int main(void)
{
    //.... init code removed.... //

    //create a semaphore using the FreeRTOS Heap
    semPtr = xSemaphoreCreateBinary();
    //ensure pointer is valid (semaphore created successfully)
    assert_param(semPtr != NULL);

To see what's going on with the source code and see how the system is reacting, we'll associate a few different LEDs with task A and task B.

Task A will toggle the green LED and give a semaphore every five times it's run through the blinking loop, as shown in the following excerpt from mainSemExample.c:

void GreenTaskA( void* argument )
{
  uint_fast8_t count = 0;
  while(1)
  {
    //every 5 times through the loop, give the semaphore
    if(++count >= 5)
    {
      count = 0;
      SEGGER_SYSVIEW_PrintfHost("Task A (green LED) gives semPtr");
      xSemaphoreGive(semPtr);
    }
    GreenLed.On();
    vTaskDelay(100/portTICK_PERIOD_MS);
    GreenLed.Off();
    vTaskDelay(100/portTICK_PERIOD_MS);
  }
}

Task B, on the other hand, will rapidly blink the blue LED three times after successfully taking the semaphore, as shown in the following excerpt from mainSemExample.c:

/**
 * wait to receive semPtr and triple blink the Blue LED
 */
void BlueTaskB( void* argument )
{
  while(1)
  {
    if(xSemaphoreTake(semPtr, portMAX_DELAY) == pdPASS)
    {   
        //triple blink the Blue LED
        for(uint_fast8_t i = 0; i < 3; i++)
        {
            BlueLed.On();
            vTaskDelay(50/portTICK_PERIOD_MS);
            BlueLed.Off();
            vTaskDelay(50/portTICK_PERIOD_MS);
        }
    }
    else
    {
        // This is the code that will be executed if we time out
        // waiting for the semaphore to be given
    }
  }
}

Great! Now that our code is ready, let's see what this behavior looks like.