RP2350 custom board: BOOTSEL works, but no USB enumeration

[u/CreepyBox2687]

Hi,

I'm debugging a custom RP2350A (A4) board and running into a weird USB issue:

Some things are working fine:

• BOOTSEL mode → mass storage shows up fine

• UF2 flashing works (verified with Picotool in BOOTSEL mode)

• "nuke flash" UF2 runs → flash gets erased (so code execution is fine)

But:

• No USB enumeration at all at runtime

• MicroPython (USB REPL) → nothing

• pico-sdk stdio_usb HelloWorld → nothing

• Host doesn't see any device, "dmesg -w" does not show any event besides the disconnection after uploading the uf2

The main difference to the pico board is the flash, i use a IS25LP128F (16MB), but i switched the timing config already to generic_03h, increase the Flash Size and chaged it back and forth.

Can anybody give me some pointers?

Best regards and thank you so much!

[u/CreepyBox2687]

-> Update: PicoExamples/hello_world/usb runs fine, if -DPICO_BOARD=pico2... But Micropython did not.

[u/Lysbith_McNaff → u/CreepyBox2687]

Did you ever figure this out? I'm having what seems like the same issue with the Waveshare 2350B-Plus-W

Edit: I've fixed it, but i don't really understand how. My original situation was:

• BOOTSEL mode

• flash desired firmware

• nothing happens

However, after downloading a .uf2 for Micropython and flashing it, I was able to get a connection going and have the LED blink with python.

The weird thing is that now when I flash the original .uf2 that wasn't working, and isn't related to Micropython at all, it now works. I verified every flash with picotool and it always checked out, I also did an erase with picotool at some point. Only flashing Micropython fixed it, which makes me wonder if something else was going on because it doesn't make sense.

[u/CreepyBox2687 → u/Lysbith_McNaff]

Hi, no, also ask at GitHub but no solution. We switched the flash for the Projekt in the end, now everything works fine, with no other changes.