measuring interrupt interval with app_timer

[paul_tanner]

I have an interrupt coming in every 50-150 microsecs and I want to measure these intervals as precisely as possible.

I tried this with SDK12.2:

APP_TIMER_INIT(0, 5, false);

then in the (GPIOTE) ISR:

uint32_t this_time=app_timer_cnt_get();

I always get zero back;

Presumably I need to initialise it in a different way?

Thx for any suggestion.

[paul_tanner]

OK. Got this after much googling.

#define NRF_DRV_TIMER_MY_CONFIG {
    .frequency          = (nrf_timer_frequency_t) NRF_TIMER_FREQ_1MHz,
    .mode               = (nrf_timer_mode_t) TIMER_MODE_MODE_Timer,
    .bit_width          = (nrf_timer_bit_width_t) TIMER_BITMODE_BITMODE_32Bit,
    .interrupt_priority = TIMER_DEFAULT_CONFIG_IRQ_PRIORITY,
    .p_context          = NULL
}

const nrf_drv_timer_t TIMER_INPUT = NRF_DRV_TIMER_INSTANCE(3);

void timer_event_handler(nrf_timer_event_t event_type, void * p_context) { 
  return;  //  needed even if not used 
}

and in main()

nrf_drv_timer_config_t in_config_f = NRF_DRV_TIMER_MY_CONFIG;
err_code = nrf_drv_timer_init(&TIMER_INPUT, &in_config_f, timer_event_handler); 
APP_ERROR_CHECK(err_code);
nrf_drv_timer_enable(&TIMER_INPUT);

then in ISR

this_time=nrf_drv_timer_capture(&TIMER_INPUT, 0);

(then handle delta microseconds and overflow.)

seems to work well enough. note that putting NULL instead of timer_event_handler causes a an immediate crash.

[paul_tanner]

Thx for that. I need to study PPI to fully understand this. I think the main point about both answers is that no extra interrupts are introduced. The timer is just available to be read in the pin interrupt's ISR. You example clears the timer which is nicer than handling overflow.