Issue flashing firmware

RE: Issue flashing firmware

Luna Harris — Mon, 09 Jun 2025 13:20:51 GMT

Hi Colby!

It sounds like you’ve run into a common issue when working with the nRF52840 dongle. The error you’re seeing (unexpected debug port ID 0, expected 2 and Could not connect to CPU core) typically points to one of two main causes:

1. Access Port (AP) protection enabled
This happens when the device has had AP (Access Port) protection set, preventing further debug access. To fix this, you might need to use Recover mode instead of Erase.
Try this command:

css

nrfjprog --recover -f nrf52 dummynation

This will attempt to reset the device to a state where you can re-flash it.

2. Hardware or connection issue
Double-check:

Are your USB cables and connections reliable?
If using a debugger (like J-Link), is it firmly attached?
Try re-plugging the dongle or using a different USB port.
Consider updating your nrfjprog tool and SEGGER J-Link drivers.

If the above doesn’t work, enable detailed logging for further insight:

css

nrfjprog --recover -f nrf52 --log

This might show you more specific clues about what’s failing.

RE: Issue flashing firmware

benjimann — Wed, 19 Mar 2025 04:52:02 GMT

Thank you, luckily I was able to read your comment.

infinite craft

RE: Issue flashing firmware

Colby G — Wed, 29 Jan 2025 05:43:43 GMT

Hello, thanks for getting back to me. I was using a J-Link EDU Mini to flash the boards. This had been working fine until it just stopped working with the dongles for some reason. I also have custom boards with the nRF52840 chipset which the EDU mini can still flash so it is very weird. I have managed to flash the boards however, I ended up using a J-Link Base Compact and was able to flash the boards successfully.

Thanks for the assistance.

RE: Issue flashing firmware

Einar Thorsrud — Mon, 27 Jan 2025 13:42:57 GMT

Hi,

I wonder if there is a problem with powering the nRF? Or that the regulator is back in 1.8 V which is the default? If so, please see the Using an external debugger in the nRF52840 Dongle Programming Tutorial, and particularily the last part, Recover after an accidental UICR erase.