nRF52840 pro mini board Bootloader issue

Other
1

I’m using a SparkFun Pro nRF52840 Mini. The board originally had working USB, and the hookup guide says it ships with a pre-programmed USB bootloader that supports CDC/DFU/MSD over native USB.

I then flashed firmware over SWD using ST-LINK + OpenOCD. SWD flashing still works fine, and OpenOCD detects/programs the nRF52840 successfully, so the chip is not dead.

After that, the board powers up, but USB no longer enumerates on Windows. I tried all recovery methods mentioned in the hookup guide:

  • double-tap reset

  • reset while holding pin 13

  • factory reset by grounding pin 2 while resetting

None of these bring back USB, and the expected flashing blue pin-7 LED for bootloader mode never appears. According to the guide, those methods should restore/enter bootloader mode and make a USB serial port or removable drive appear.

My conclusion is that I likely overwrote or corrupted the USB bootloader region while flashing via SWD. Since SWD still works but all bootloader-entry methods fail, I think I now need the correct SparkFun/compatible bootloader image to restore over SWD. The hookup guide also points to the SWD interface specifically for bypassing/recovering from bootloader problems.

2

That board uses this bootloader GitHub - adafruit/Adafruit_nRF52_Bootloader: USB-enabled bootloaders for the nRF52 BLE SoC chips · GitHub - Give it a whirl and see how it goes :smiley:

3

Thanks. I checked the Adafruit nRF52 bootloader repo. I can see prebuilt release assets, but I do not see SparkFun Pro nRF52840 Mini in supported_boards.md or an obvious matching release asset. Can you please tell me the exact board target name or link the exact prebuilt bootloader .hex I should flash over SWD for the SparkFun Pro nRF52840 Mini?

4

It appears that’s because the list wasn’t didn’t updated to include it :-/

Everything I’ve seen points to the main Adafruit release for ours - give that’n a try (our resources section also points to the same Adafruit Bootloader, labeled ‘source’ i our docs)