Two interrupt events on TIMER0

Question

Hi,

This may be a silly question but I'm trying to generate two timed interrupt events using only TIMER0 (the MCU is nrf51822). My code is:


#define TIMEOUT1 3000    //3s
#define TIMEOUT1 5000    //5s

  NRF_TIMER0->TASKS_STOP = 1;
  // Create an Event-Task shortcut to clear TIMER0 on COMPARE[0] event
  NRF_TIMER0->MODE        = TIMER_MODE_MODE_Timer;
  NRF_TIMER0->BITMODE     = (TIMER_BITMODE_BITMODE_24Bit << TIMER_BITMODE_BITMODE_Pos);
  NRF_TIMER0->PRESCALER   = 4;  // 1us resolution

  NRF_TIMER0->TASKS_CLEAR = 1;               // clear the task first to be usable for later
  NRF_TIMER0->CC[0] = TIMEOUT1 * 1000; //first timeout
//  NRF_TIMER0->CC[1] = TIMEOUT2 * 1000;   //second timeout

  NRF_TIMER0->INTENSET    = TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos;
  /* Create an Event-Task shortcut to clear TIMER0 on COMPARE[0] event. */
  NRF_TIMER0->SHORTS      = (TIMER_SHORTS_COMPARE1_CLEAR_Enabled << TIMER_SHORTS_COMPARE1_CLEAR_Pos);

The irq handler function then is: {code} void TIMER0_IRQHandler(void) { if( (NRF_TIMER0->EVENTS_COMPARE[0] != 0) && (NRF_TIMER0->INTENSET | (TIMER_INTENSET_COMPARE0_Set << TIMER_INTENSET_COMPARE0_Msk))) { NRF_TIMER0->EVENTS_COMPARE[0] = 0; } if( (NRF_TIMER0->EVENTS_COMPARE[1] != 0) && (NRF_TIMER0->INTENSET | (TIMER_INTENSET_COMPARE0_Set << TIMER_INTENSET_COMPARE0_Msk))) { NRF_TIMER0->EVENTS_COMPARE[1] = 0; } } {/code}

When I run the code, I only see an interrupt when TIMEOUT1 is met. I've probably misunderstood how the timer mechanism works. One theory I have is because I use the SHORTS, the counter is reset to 0 so only the first timeout is triggered followed by a counter reset repeatedly. I tried to disable SHORTS but then I noticed that an interrupt is triggered quite unpredictably and with long pauses. So the question is: is it possible to have TIMER0 triggering two interrupts at different intervals? If so then what am I doing wrong?

To solve my problem I use now TIMER0 and TIMER1 which works fine.

Håkon Alseth · Accepted Answer

Hi,

Tested your code, and it seems that you forgot to enable interrupt on COMPARE1. Here's my test code:


void init_timer(void)
{
    NRF_TIMER0->TASKS_STOP = 1;
    // Create an Event-Task shortcut to clear TIMER0 on COMPARE[0] event
    NRF_TIMER0->MODE        = TIMER_MODE_MODE_Timer;
    NRF_TIMER0->BITMODE     = (TIMER_BITMODE_BITMODE_24Bit << TIMER_BITMODE_BITMODE_Pos);
    NRF_TIMER0->PRESCALER   = 4;  // 1us resolution

    NRF_TIMER0->TASKS_CLEAR = 1;               // clear the task first to be usable for later
    NRF_TIMER0->CC[0] = TIMEOUT1 * 1000; //first timeout
    NRF_TIMER0->CC[1] = TIMEOUT2 * 1000;   //second timeout

    NRF_TIMER0->INTENSET    = TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos;
    NRF_TIMER0->INTENSET    = TIMER_INTENSET_COMPARE1_Enabled << TIMER_INTENSET_COMPARE1_Pos;
    /* Create an Event-Task shortcut to clear TIMER0 on COMPARE[0] event. */
    NRF_TIMER0->SHORTS      = (TIMER_SHORTS_COMPARE1_CLEAR_Enabled << TIMER_SHORTS_COMPARE1_CLEAR_Pos);
    NRF_TIMER0->TASKS_START = 1;
}

int main(void)
{
    NVIC_EnableIRQ(TIMER0_IRQn);
    init_timer();
    while(1);
}

void TIMER0_IRQHandler(void) 
{
    if (NRF_TIMER0->EVENTS_COMPARE[0] != 0)
    {
        NRF_TIMER0->EVENTS_COMPARE[0] = 0;
    }
    if (NRF_TIMER0->EVENTS_COMPARE[1] != 0)
    {
        NRF_TIMER0->EVENTS_COMPARE[1] = 0;
    }
}

BR Håkon

Two interrupt events on TIMER0

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