FreeRTOS : How to measure context switching time?

I want to measure the overhead of context switching time.

Here is my idea to do that:

There are two task:

  1. taskA
  2. idle

I create a task as below:

void calculate_ct(void *pvParameters)
{
    int i = 0; 
    for(; i < 100; i++)
    {
        vTaskDelay(100 / portTICK_RATE_MS); // delay 100 ms
    }    
    // get_time();
    vTaskDelete(NULL);
}

When task call vTaskDelay() , it will turn into block state. It means that happen a context switch to idle task.

Can I use get_time() at the end and minus the delay time(10 * 100ms) to get the total overhead of context switching time and make the overhead divide by 10 to get the average of the overhead of context switching time?

get time() as below:

unsigned int get_reload()
{
    return *(uint32_t *) 0xE000E014;
}

unsigned int get_current()
{
    return *(uint32_t *) 0xE000E018;
}

unsigned int get_time()
{
    static unsigned int const *reload = (void *) 0xE000E014;
    static unsigned int const *current = (void *) 0xE000E018;
    static const unsigned int scale = 1000000 / configTICK_RATE_HZ;
                                    /* microsecond */
    return xTaskGetTickCount() * scale + (*reload - *current) * (1.0) / (*reload / scale);
}


Source: linux

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.