Cannot Buttonless DFU on nrf52840

[mredp]

Hi,

This is unrelated to my other open question. 

I have programmed the secure ble bootloader and can OTA flash the buttonless bootloader example.

My problem is that when I try to perform a buttonless update, the device restarts back into the app.

This issue does not happen on my nrf52832 dev board (s132). Only on my nrf52840 custom board (s140). 

From what I can tell, the GPREGRET register is being set before the device restarts. But the bootloader doesn't read it correctly on boot.

Any help is greatly appreciated, I have spent a long time changing the configs and retrying. I have tried on gcc 8.3.1 and gcc 6.3.1. Even with my custom app, I can buttonless dfu on the nrf52832 but not the nrf52840. 

[Einar Thorsrud]

Hi,

This mechanism is exactly the same on nRF52832 and nRF52840, so that itself should not be relevant.

I recommend you flash the debug bootloader with RTT logging as the first step. The logging is quite extensive, and in many cases, you can read directly out of the log what has happened. If not, you can add more log output in the relevant region. The relevant part of the bootloader is where it reads the retention register, looking for BOOTLOADER_DFU_START (assuming a recent SDK) in dfu_enter_check() in nrf_bootlaoder.c. If that is not set at that point, then it is either cleared before it is read or never written in the first place.

[mredp]

A new board arrived with the ISP-1807 module and this now works fine. For some reason it was not working on the previous module the BC840. Thanks for your help.