app timer frequency increasing

[nrbrook]

I'm building a firmware for nRF52 which is using app timer v2 with RTC1. After a while, app_timer starts running many times faster than normal, and I'm not sure why. Nothing seems to happen to trigger it. Here is RTC1 while operating normally:

And here when the timer is running too fast:

Perhaps there is some memory corruption or something...what controls the app_timer speed other than RTC configuration? The RTC counter is increasing at a faster rate, to the point where a 1s timer occurs very rapidly (probably a few ms).

The LFCLK state is:

i.e. RC source. So it appears RC oscillator is running fast...why would that be?

[nrbrook]

Ok, I will try. I definitely didn't pause the debugger for 144 seconds though.

[nrbrook]

Here is my code:

NRF_RTC1->EVTEN     = (RTC_EVTENSET_TICK_Msk );

    // configure GPIOTE
    NRF_GPIOTE->CONFIG[0] = ( (GPIOTE_CONFIG_MODE_Task      << GPIOTE_CONFIG_MODE_Pos)
                              | (9                  << GPIOTE_CONFIG_PSEL_Pos)
                              | (GPIOTE_CONFIG_POLARITY_Toggle << GPIOTE_CONFIG_POLARITY_Pos) )
                            | (0 << GPIOTE_CONFIG_OUTINIT_Pos);

    // configure PPI
    NRF_PPI->CH[0].EEP    = (uint32_t)(&NRF_RTC1->EVENTS_TICK);
    NRF_PPI->CH[0].TEP    = (uint32_t)(&NRF_GPIOTE->TASKS_OUT[0]);
    NRF_PPI->CHENSET      = PPI_CHENCLR_CH0_Msk;
    NRF_RTC1->TASKS_START = 1;

However, I only see a low voltage waveform on pin 9, and the frequency isn't correct. Is this code correct? I just copied from your link and removed the timer related code. app_timer sets up the RTC before this code runs.

[Einar Thorsrud]

Hi Nick,

GPIO pin 9 (P0.09) is one of the NFC pins so it will act as a NFC pin by default. Have you changed it to be a GPIO pin in the UICR (the easiest is to define CONFIG_NFCT_PINS_AS_GPIOS for your project to do this)? The NFC pins also have high capacitance so they may not be the best choice in any case, though.

[nrbrook]

Ah yes ok. It works correctly on pin 0. Now I'll wait until it happens again...