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.

[AmbystomaLabs]

See above. I can only answer once so I added the code to my previous answer.