nRF52840DK stopped connecting in intermediate course lesson 8 exercise 2

[craig.goldman]

I was working through Nordic Intermediate course lesson 8 exercise 2 - DFU over USB, adding external flash and custom keys.
I was using an nRF5280DK.  (Sticker: PCA10056 2.0.1 2020.33) and my PC running Windows 10.
All work was done using Visual Studio Code.

I got through all the parts of step#7 where the firmware is downloaded using the nRF USB port on the DK.   All went well; firmware downloaded and executed correctly - LED1 blinking appropriately.

During step#8, the PC is connected again to the DK debug port; but Visual Studio Code shows no devices connected.
The DK is powered and blinking LED1 shows it is running the last code downloaded by the bootloader using the USB.
The PC Device Manager also shows no COM Ports on the PC USB.

What happened? Can this be fixed? Have I bricked the DK following the lesson8 instructions?

-Craig Goldman

[Menon]

Hello,

Have I bricked the DK following the lesson8 instructions?

It seems that your nRF52840 DK is still operational but is not being detected by the PC after performing the DFU over USB. Although the device appears to be functioning correctly (as indicated by LED1 blinking), it may not be exposing the expected USB interfaces.

Try resetting the device and check if it can be accessed using nrfjprog commands. For example, you could run nrfjprog --recover from the command line and review the output. Also, see if the device appears in the nRF Programmer app within nRF Connect for Desktop.

Kind Regards,

Abhijith

[craig.goldman]

nrfjprog --recover returns... ERROR: No debuggers were discovered.

No devices show in nRF Programmer app within nRF Connect for Desktop.

I double-checked with a different development board; that board shows up in nRF programmer.

Any other thoughts?

[craig.goldman]

One more piece of information.  I'm not sure the reset button has any effect on the running program.

[Menon]

Hello,

I'm not entirely sure, but the issue might be due to the onboard debugger being compromised during the DFU process. If you have another DK, you can try using it as an external debugger to access the non-working board. Connect the Debug Out (P19) of the DKs to each other using a 10-pin Serial Wire Debug (SWD) cable.

Kind Regards,

Abhijith

[craig.goldman]

I do not have a 10-pin serial cable with the small female connector which can plug into P19. Do you know if Digikey or someone else sells this type of cable?

If I acquire the cable, does the other end plug into P18 of the "bad" board?

Once the two boards are connected, is there a way to re-program the onboard debugger?  Is there something else which should be done? Is there documentation on this entire process?