verifying 32kHz crystal accuracy

[_AW]

We have a custom board that is using the RTC with an external 32.768kHz crystal.  I would like to verify the accuracy and tune the capacitors if necessary.  I want to verify that what I am doing is reasonable.

We are using Zephyr.  I have set up

CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=y

static struct k_timer mTimer;

static void on_timer(struct k_timer *timer)

{

    pin_traces_auto_toggle(tp_pin_7);

   // pin_traces_toggle(tp_pin_6,k_is_in_isr());

}

int main(void)

{

    __ASSERT_NO_MSG(log_initialize());

    __ASSERT_NO_MSG(pin_traces_initialize());

    k_timer_init(&mTimer, on_timer, NULL);

    k_timer_start(&mTimer, K_SECONDS(1), K_SECONDS(1));

    return 0;

}

This timer will be based on the 32.768kHz crystal, correct?  I am watching the GPIO signal on what we have defined as test point 7 over a long period to verify the accuracy.  I get (basically) a 1 second toggle off this pin.  Is it reasonable to use this for checking crystal accuracy?

[Kazi Afroza Sultana]

Hello,

''This timer will be based on the 32.768kHz crystal, correct? ''

yes LF 32.768 KHz is correct, if you just use PPI to toggle a GPIO pin on every RTC click, not a timer like this.

There is a sample in NCS that can be used for testing this (https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/debug/ppi_trace/README.html) 

Thanks.

BR

Kazi

[underpickled]

Hi, I'm trying to use this example for the same purpose as the OP, but the example gives several build errors, including

.../nrf/subsys/debug/ppi_trace/ppi_trace.c: In function 'get_gpiote':
.../nrf/subsys/debug/ppi_trace/ppi_trace.c:56:22: error: unknown type name 'nrfx_gpiote_t'

and

.../nrf/subsys/debug/ppi_trace/ppi_trace.c:129:13: error: too many arguments to function 'nrfx_gpiote_channel_alloc'
  129 |         if (nrfx_gpiote_channel_alloc(gpiote, &channel) != NRFX_SUCCESS) {
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~
.../modules/hal/nordic/nrfx/drivers/include/nrfx_gpiote.h:185:12: note: declared here
  185 | nrfx_err_t nrfx_gpiote_channel_alloc(uint8_t * p_channel);

I'm using SDK 2.6.0.

Thanks!