How to use an RTC as an external 32 kHz oscillator

[Kampino]

My design uses an RV-3028 RTC as an external 32 kHz oscillator for the application timer. Do I have to configure the SDK to use an external oscillator instead of a crystal?

There is an issue with the application timer too. The timer doesn´t work after I have reprogrammed my chip (the oscillator outputs the 32 kHz clock). The problem is gone and the application timer works as expected after the watchdog hits and reset the system (because the application timer doesn´t reset the watchdog after programming). The problem doesn´t appear when I use my NRF52DK which has an on-board 32 kHz crystal, so I assume that there is some malfunction with the external oscillator.

[Kenneth]

Do I have to configure the SDK to use an external oscillator instead of a crystal?

The BLE softdevices do not support external oscillator, so you need to use the internal RC oscillator or an external crystal.

[Kampino]

What´s the reason for this? Would be a neat solution when I can use the RTC as a 32 kHz oscillator

[Kenneth]

I would think a combination of very little demand and potentially much more testing.

Kenneth