Issue with Unknown Device detection on nRF5340 – Flashing works, but Debugging/Recovery fails

[gwan0624]

I am currently developing a project using an nRF5340DK and a custom board.

For some unknown reason, the device is being identified as an "Unknown device."


The ironic part is that flashing the firmware still works successfully, even though the device ID isn't recognized correctly.

However, when I attempt to start debugging, I encounter the following error:

I suspect that the Application Core is protected (APPROTECT), which prevents the debugger from correctly identifying the nRF5340 IC on my custom board.

I tried to perform a recovery to resolve this, but the recovery process also fails with the following error:

How can I get the debugger to correctly recognize the device as NRF5340_xxAA_REV1 again instead of "Unknown device"?

[Vidar Berg]

Hello,

Yes, as you say, nrfutil will not be able to correctly identify the chip when approtect is enabled. To unlock approtect on the nRF5340, you must perform the recovery procedure on the network core before you recover the application core. Please try this and see if the problem persists.

nrfutil device recover --core network
nrfutil device recover

Best regards,

Vidar

[gwan0624]

Thank you for your response.

Unfortunately, the recovery was unsuccessful even after following the procedure. Given the unstable outputs on the VDD and RESET pins, it appears the MCU itself has been damaged.

 Issue with failing VDD output – Is recovery possible? (nRF5340) 

I will need to reorder the PCB and proceed with further testing

Best regards,
gwan0624

[Vidar Berg]

Does your design include the optional DCDC inductors? If you build the FW for the nRF5340 DK, the DCDC regulators will be enabled by default, and if the inductors are not included, the regulator will fail to provide a stable supply voltage internally in the chip which commonly leads to issues such as being unable to re-program the chip.

Best regards,

Vidar

[gwan0624]

I'm using LDO mode without an inductor and updated the overlay file accordingly.

Is it possible the power instability is because the nRF5340 is still stuck in DCDC mode? Since the device fails to boot, I suspect the internal regulator registers haven't actually changed to LDO mode.

[Vidar Berg]

Your overlay is correct, so if it is being applied it should not be an issue with the regulator settings. If you want to confirm that it is being applied, you can check the final DT configuration in the zephyr.dts file generated for your application in the build folder. You can also try to read the regulator registers with nrfutil (if it doesn't fail to connect).

Reading VREGMAIN.DCDCEN:

nrfutil device read --address 0x50004704 --direct