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App_timer expires immediately - SDK 10

I am seeing a problem identical to what's described in this question. I'm using SDK version 10.

My timers work fine for a while, but then suddenly and seemingly at random all timers expire the instant they are started. Sometimes it goes away and the timers work again, but sometimes the only fix seems to be a restart.

I've seen two suggested solutions. One is to add a delay or a call to rtc1_compare0_set in compare_reg_update; I'm on SDK 10 and both solutions are already there:

    ...
    rtc1_compare0_set(rtc1_counter_get());  // this should prevent CC to fire again in the background while the code is in RTC-ISR
    nrf_delay_us(MAX_RTC_TASKS_DELAY);
    timer_timeouts_check_sched();
    ...

The only other solution I've found on the forum is to have a dummy timer that is always running. It's recommended in this answer.

Sadly, I do already have a dummy timer always running—I've been using it to force the RTC to stay on so I can use it for timekeeping.

Are there any other known problems or solutions with app_timer? I'm running out of ideas. Thanks!

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  • I think there may also be something incorrect happening in list_insertions_handler. If no timer has expired for more than half of the RTC duration then m_ticks_latest won't have been updated during this time. list_insertions_handler will fail this check:

        if (
             ((p_timer->ticks_at_start - m_ticks_latest) & MAX_RTC_COUNTER_VAL)
             <
             (MAX_RTC_COUNTER_VAL / 2)
            )
    

    delta_current_start will be set to a very large value, and the timer's ticks_to_expire will get set to 0.

    This means that if you have a timer running with a timeout greater than MAX_RTC_COUNTER_VAL/2 and don't expire any timers for just over MAX_RTC_COUNTER_VAL/2, then setting a timer with a reasonable timeout will cause it to expire immediately.

    This is also relevant because it doesn't work with my patch above. See next comment.

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  • I think there may also be something incorrect happening in list_insertions_handler. If no timer has expired for more than half of the RTC duration then m_ticks_latest won't have been updated during this time. list_insertions_handler will fail this check:

        if (
             ((p_timer->ticks_at_start - m_ticks_latest) & MAX_RTC_COUNTER_VAL)
             <
             (MAX_RTC_COUNTER_VAL / 2)
            )
    

    delta_current_start will be set to a very large value, and the timer's ticks_to_expire will get set to 0.

    This means that if you have a timer running with a timeout greater than MAX_RTC_COUNTER_VAL/2 and don't expire any timers for just over MAX_RTC_COUNTER_VAL/2, then setting a timer with a reasonable timeout will cause it to expire immediately.

    This is also relevant because it doesn't work with my patch above. See next comment.

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