sd_softdevice_enable does not return

[wouchida]

On one of our products, we are experiencing approximately 4% failures during production.  I traced the problem to be caused by function sd_softdevice_enable not returning.  This problem does not occur if I have a Segger JTAG probe connected or if the internal LF 32 KHz RC oscillator is used instead of the external crystal.  But with the external 32 KHz (20 ppm) crystal oscillator, about 4% of boards do not return from the sd_softdevice_enable function.  On the problem boards, our hardware engineers believe that this LF external oscillator is starting up normally.  They do not observe any startup differences between a good board or a bad board.  I would like to know the reasons why the function sd_softdevice_enable might not return.

[Kenneth]

Hi,

The only 'wait state' in the softdevice enable is the wait for the lfclk started event. So likely the external crystal do not start as expected.

Best regards,
Kenneth

[eiadj]

Hi Kenneth,

We've looked at a number of units - some working, some non-working - and the 32kHz crystal starts-up identically in both scenarios (see attached screenshots). We've also verified that the parameters of the oscillator operation are accurate (frequency, amplitude, offset).

Furthermore, swapping the crystal and capacitors does NOT cause a defective board to start functioning and moving the crystal+caps from a defective board to a good board doesn't affect functionality.

What would be the next things to look at that could be causing a malfunction of the softdevice_enable function?

Best,

Eiad Jandali

Hardware Engineer

XTAL start-up on a functioning board

XTAL start-up on a non-functioning board

[Kenneth]

What if you start it manually before softdevice init like this:

NRF_CLOCK->LFCLKSRC = (CLOCK_LFCLKSTAT_SRC_Xtal << CLOCK_LFCLKSTAT_SRC_Pos);
NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
NRF_CLOCK->TASKS_LFCLKSTART = 1;
while(NRF_CLOCK->EVENTS_LFCLKSTARTED == 0)
;
NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;

Still waiting for datasheet and part number for the 32kHz crystal.

Best regards,
Kenneth

[wouchida]

If I start it manually prior to the call of sd_softdevice_enable, the oscillator starts and the call to sd_softdevice_enable doesn't hang.  Also, using the internal RC oscillator, running with a Segger JTAG probe, configuring RTC1, PPI and GPIOTE to output a 16 KHz clock derived from this 32 KHz oscillator, or creating a timer2 interrupt using the HF oscillator causes this function not to hang.  I created a timer2 interrupt so I could monitor the state of this oscillator while sd_software_enable was in a hung state.     

[eiadj]

Hi Kenneth,

The crystal is provided by Siward - part number for the crystal is XTL741-F98-116

Attached is the specification sheet for the part.

Best,

Eiad Jandali

Siward_XTL741-F98-116_32.768kHz.pdf

[Kenneth]

Hi,

The crystal looks good. Were you able to do the manual test?

What SDK and SD are you using btw?

Best regards,
Kenneth