Any way to control wether ext. 32k XTAL works properly?

[Valer_I]

Hello all,

Our product based on nRF51 is on preproduction stage. We use both 16MHz and 32kHz external crystals. The question is: Is there any way to check programatically if 32kHz crystal soldered/soldered properly/works fine?

We noticed that on SD110 v8.0.0 device works even without external 32k crystal with software defined as

if (NRF_SUCCESS !=(err_code=sd_softdevice_enable((uint32_t)NRF_CLOCK_LFCLKSRC_XTAL_75_PPM, softdevice_assert_callback)))...

However, in that case the current consumption increased significantly. And it could cause problems in post production testing.

Best regards,

[Ole Bauck]

If you call sd_softdevice_enable() with LFCLKSRC_XTAL and there is no external crystal, the code will be stuck waiting for the crystal to start.

You can start a watchdog timer (WDT) before initializing the stack. This will reset the chip if a reload register is not set before a certain amount of time. In NRF_POWER->RESETREAS you can check what caused a reset. Remember that the NRF_POWER->RESETREAS register is cumulative, which means that the register is not cleared if the reset source is not power-on-reset or brown out reset. You can clear a field in the register by writing a "1" to it.

This code will setup a watchdog:

NRF_WDT->CRV = 32768*10;   //ten seconds
NRF_WDT->RREN = (WDT_RREN_RR0_Enabled << WDT_RREN_RR0_Pos);
NRF_WDT->TASKS_START = 1;

You have to reload it regulary to avoid resetting:

NRF_WDT->RR[0] = 0x6E524635;

Check the reset reason like this (does not clear the register value):

if(NRF_POWER->RESETREAS & (POWER_RESETREAS_DOG_Detected <<    POWER_RESETREAS_DOG_Pos))
{
    printf("Chip was reset by watchdog!\n");
}