EVENTS_LFCLKSTARTED event when using external LF clock source

[Mindaugas Tinteris]

I am using clock signal from external RTC chip to clock NRF52832 at 32768 Hz through XL1 leaving XL2 floating. I have verified the waveform by the oscilloscope and set SRC to 1, BYPASS to 1 and EXTERNAL to 1 in LFCLKSRC register, but there still is a problem that device hangs in a loop inside softdevice code, in a place where it waits for EVENTS_LFCLKSTARTED event.

Is EVENTS_LFCLKSTARTED event still generated even when using external LF clock source instead of XTAL? Or maybe it is a flaw in softdevice's logic?

[MartinBL]

Hi,

1. What Softdevice version are you using?
2. How do you know it is waiting for that specific event?
3. I assume that the RTC generates a rail-to-rail signal?

[Mindaugas Tinteris]

1. s132_nrf52_5.0.0_softdevice and NRF5 SDK v14.1.0;
2. I am stepping using a debugger and have examined assembly code. It checks register at 0x40000104 which stands for EVENTS_LFCLKSTARTED and if it is equal to 0 goes to WFI instruction. Since I am in a debug mode it doesn't go to sleep there and repeats that checking and WFI cycle again and again;
3. yes, it's rail to rail 0 to 1.8V (Vcc).

[Kenneth]

Hi, currently the softdevice api does not support external LFCLK clock, however can you create a MyPage case so we can look at this in more details?

[Mindaugas Tinteris]

Small update: our hardware engineer tried different approaches and found out, that system starts normally only when external CLK signal is routed to both XL1 and XL2 simultaneously. All other configurations, described in the datasheet doesn't work. How could it be? Is there some error in the datasheet?