nrf_drv_timer is not accurate

[brianbscho]

Hi,

I wanted to create fixed rate waveform. I first used nrf_delay_us with nrf_gpio_pin_toggle. But I realized it is not accurate enough to do it, especially when the device is advertising and bluetooth pairing happens.

So I changed it to use nrf_drv_timer. Below is how I'm doing it (main app is using APP_TIMER).

const nrf_drv_timer_t HALF_TIMER = NRF_DRV_TIMER_INSTANCE(1);

void timer_event_handler(nrf_timer_event_t event_type, void* p_context)

{

switch(event_type)

{
    case NRF_TIMER_EVENT_COMPARE1:
	nrf_gpio_pin_toggle(LEFT_PIN);
	nrf_gpio_pin_toggle(RIGHT_PIN);
        break;
    
    default:
        //Do nothing.
        break;
}

}

void TimerInit ()

{

nrf_timer_frequency_set(HALF_TIMER.p_reg, NRF_TIMER_FREQ_1MHz);
nrf_drv_timer_init(&HALF_TIMER, NULL, timer_event_handler);
uint32_t time_ticks = nrf_drv_timer_us_to_ticks(&HALF_TIMER, HALF_CLOCK); //HALF_CLOCK is 200

nrf_drv_timer_extended_compare(
     &HALF_TIMER, NRF_TIMER_CC_CHANNEL1, time_ticks, NRF_TIMER_SHORT_COMPARE1_CLEAR_MASK, true);

nrf_drv_timer_enable(&HALF_TIMER);

}

But still it doesn't work accurately. Result is like below.

Like the capture shows, sometimes longer wave happens (I didn't capture it but shorter wave also happens). How can I fix it? Can anyone suggest me how to avoid such behavior?

Thanks, Brian

[RK]

Please use the search box at the top. There must be 4-5 posts a week with people trying and failing to use timers when the softdevice is running for accurate timing. It doesn't work.

Search for PPI/PWM

[brianbscho]

I searched it already with the term "nrf_drv_timer" but nothing was helpful. I know it doesn't work. That's why I asked the question, isn't it? I believe, if so many people were asking same problem every week, it's not because they didn't use the search box but because the product was not good enough.