Bootloader resets at some point in nRF52820

[Louis_263]

Hello,
I am working on jumping from the app to the bootloader to do a firmware update from there. If I don't have any application firmware on the nRF, the DFU also works without problems.
However, when I jump from the application to the bootloader (via the GPREGRET method), the bootloader resets at a certain point in the code and the value of the GPREGRET register is reset, so no DFU can be performed.
Is there any reason why the bootloader could be reset? E.g. by any interrupts?  

BR

Louis

[Louis_263]

Update: If I put the if-instruction for the GPREGRET method at the top of the function dfu_enter_check (see picture) it works... very strange

[Susheel Nuguru]

That seems very strange especially the rest of the if conditions before the change also evaluate to true.

[Louis_263]

Do any of these functions change the value in the GPREGRET register or call an NVIC_SystemReset? Otherwise I can't think of any reason for this... In my application I use a watchdog and then jump to the bootloader when DFU. I had thought that the watchdog might cause a reset, but it is automatically fed in the bootloader code.

[Susheel Nuguru]

You should be able to put a breakpoint at all the NVIC_SystemReset occurance in your code and run in debug mode. You will then get the context of getting a soft reset with the function call stack in your debugger to get more context.