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FreeRTOS Exercise Lab21

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FreeRTOS Exercise Lab21

  1. Program TIMER0 for 500ms periodic interrupt
    Timer programming How to ...
  2. Create Task 1 as a continuous processing task, and Task 2 (interrupt handler task) as the task to which interrupt processing is deferred.
    In Task 1, display "Task 1 is Running."
  3. Display "Timer Interrupt Handler Task is Running" in the Task 2


/* Task 1 is continuous processing Task */
void vTask1(void *pvParameters)
{
    for(;;) {
        printf("%s", "Task1 is Running.\n\r");
        for(volatile auto uint32_t ul = 0; ul < 0xffff; ul++ ){ ; }
    }
}
 
/* Task 2 as Timer0A Interrupt handler task */
void vTask2(void *pvParameters)
{
    for(;;) {
        if( xSemaphoreTake(xTimer0ASemaphore, portMAX_DELAY) ) {
            printf("%s", "Timer Interrupt Handler Task is Running");
        }
    }
}
 
/* Timer0A Interrupt Service Routine */
void vTimer0A_ISR(void)
{
    BaseType_t xTaskWoken;
 
    TIMER0_ICR_R = 0x01;            /* clear Timer0A timeout interrupt */
 
    xSemaphoreGiveFromISR(xTimer0ASemaphore, &xTaskWoken);
    if(xTaskWoken) {
        portYIELD_FROM_ISR(xTaskWoken);
    }
}

How it works ...

The deferred processing task uses a blocking ‘take’ (xSemaphoreTake(xTimer0ASemaphore, portMAX_DELAY)) call to a semaphore as a means of entering the Blocked state to wait for the event to occur. When the event occurs, the ISR uses a ‘give’ (xSemaphoreGiveFromISR(xTimer0ASemaphore, &xTaskWoken)) operation on the same semaphore to unblock the task so that the required event processing can proceed.


Freertos interrupt and handler task.png
Figure: Using a binary semaphore to implement deferred interrupt processing


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