External 32kHz crystal detection

RE: External 32kHz crystal detection

awneil — Mon, 19 Oct 2020 07:20:57 GMT

[quote userid="93391" url="~/f/nordic-q-a/65805/external-32khz-crystal-detection/275482#275482"] I think you can close the ticket now[/quote]

You do that with the 'Verify Answer' button:

RE: External 32kHz crystal detection

Vincent G. — Mon, 19 Oct 2020 06:34:18 GMT

Hi,

Thanks for the explanation. I think you can close the ticket now.

Regards,

Vincent

RE: External 32kHz crystal detection

Sigurd — Fri, 16 Oct 2020 15:32:43 GMT

Hi,

We suspect that the noise injection on XL1(P0.00) and/or XL2(P0.01) could be enough to trigger the event EVENTS_LFCLKSTARTED, and be propagated to the clock output even if no crystal is mounted, and even if XL1/XL2 is grounded. The clock oscillator was not designed for this use-case. The behavior might vary from chip-to-chip, and seems to also depend on the noise level on VDD.

RE: External 32kHz crystal detection

Vincent G. — Mon, 12 Oct 2020 07:59:25 GMT

Hi Sigurd,

Thanks for the workaround.

Keep me posted if you get any info about the issue from your team.

Best regards,

Vincent

RE: External 32kHz crystal detection

Sigurd — Wed, 07 Oct 2020 11:15:05 GMT

[quote user="Vincent G."]Did you get any answers from your team ?[/quote]

The team has not seen this issue before. We are investigating the issue.

[quote user=""]But waiting more that 250µS doesn't seem to be a reliable way to detect the absence of crystal.[/quote]

We are still looking into this, but as a workaround to detect whether a crystal is mounted, we might suggest something like this:

If LFCLKSTARTED event has not come after 1 second, conclude that no crystal is connected
If LFCLKSTARTED event has come within 1 second, measure LFCLK frequency
If LFCLK frequency is not "close" to 32768Hz then conclude that no crystal is connected

The 1 second wait may be shortened, but it depends on the crystal.

RE: External 32kHz crystal detection

Vincent G. — Thu, 01 Oct 2020 07:05:17 GMT

Hi Sigurd,

Did you get any answers from your team ?

Vincent

RE: External 32kHz crystal detection

Sigurd — Thu, 17 Sep 2020 14:40:16 GMT

Hi,

I was able to reproduce this on a different nRF52832 DK.

I will check with the team if they have seen this before.

RE: External 32kHz crystal detection

Vincent G. — Wed, 16 Sep 2020 12:47:33 GMT

I tested this on two other pca10040 and I can reproduce on both of them.

Marking on NRF52 is nrf52QFAAB0. Maybe you tested on an earlier revision?

RE: External 32kHz crystal detection

Vincent G. — Tue, 15 Sep 2020 13:00:06 GMT

Hi,

I have just tested your fix and it doesn't change anything.

My code :

    /* Start LFCLK with external 32kHz XTAL */
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
    NRF_CLOCK->LFCLKSRC = (CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos);
    __DSB();
    nrfx_clock_anomaly_132();
    NRF_CLOCK->TASKS_LFCLKSTART = 1;
    __DSB();
    while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0)
    {
    }

If I hit the reset button on a board without 32kHz crystal it boot in approx. seconds.

Also I have noticed something on boards with a crystal :

Just after flashing, crystal startup time takes more than 250ms, between 380ms and 500ms. After reset the 32kHz crystal start in 250ms. Is this something expected ?

Vincent

RE: External 32kHz crystal detection

Sigurd — Mon, 14 Sep 2020 12:36:40 GMT

Hi,

I was not able to reproduce this on a nRF52832DK without LF crystal.

But, could you try to add this errata 132 delay, before starting the LFCK, and see if it fixes the issue? Similar to how it's done here.