Occasional long cycles (jitter) on looping timer

[Chris Ergo]

I use the following code to enable a timer that clears itself to loop continuously via the compare0-clear shortcut. (I then use other compares, PPI, and GPIOTE to output pulses.) The timing is very solid except occasionally (randomly about once per second on average) the cycle is long by consistently about 200us (about 10% of a cycle). What could cause this?

#define IR_SAMPLE_PERIOD_nS         2008032
const nrf_drv_timer_t IR_DRV_AND_SAMPLE_TIMER = NRF_DRV_TIMER_INSTANCE(4);
...
    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    APP_ERROR_CHECK(nrf_drv_timer_init(&IR_DRV_AND_SAMPLE_TIMER, &timer_cfg, timer_event_handler));

    time_ticks = timer_ns_to_ticks(&IR_DRV_AND_SAMPLE_TIMER, IR_SAMPLE_PERIOD_nS);

    nrf_drv_timer_extended_compare(
         &IR_DRV_AND_SAMPLE_TIMER, NRF_TIMER_CC_CHANNEL0, time_ticks, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, true);

[Chris Ergo]

I found the problem. It is in my software. I had added code that resets the timer if interrupts aren't serviced fast enough and things get out of sync. I need to change how I handle that.

Stian Røed Hafskjold, I'm sorry to bother you with all of this. Thank you for your help.

[Stian Røed Hafskjold]

Ok, thanks for reporting back. Glad you figured it out.