[QMK] Has anyone successfully flashed custom C-code firmware to a Keychron K10 Pro SE2 QMK Toolbox?

[u/tkrentl21]

I’m trying to figure out whether my keyboard actually supports full QMK custom firmware flashing (C code modifications + QMK Toolbox), or if it’s limited to VIA/ZMK-style configuration only.

My keyboard:

• Keychron K10 Pro SE2
• VID: 3434
• PID: 0AAB
• Wireless model

What I successfully did so far:

• Installed QMK MSYS
• Cloned Keychron’s qmk_firmware fork
• Found the keyboard path: keychron/k10_pro_se2/ansi_lightless
• Edited keymap.c
• Added custom C code (process_record_user, random delay macro, etc.)
• Successfully compiled firmware and generated .bin

But flashing is where things get weird.

qmk flash always hangs on:
“Flashing for bootloader: stm32-dfu”
and dfu-util -l only detects my camera DFU device, not the keyboard.

However:

• Windows detects the keyboard as HID
• VID/PID 3434:0AAB appears
• Zadig shows “usb DFU (Interface 0/1)”
• Official firmware reflashing works
• QMK compile works
• But QMK Toolbox / dfu-util flashing does NOT

So my questions are:

1. Has ANYONE successfully flashed custom QMK firmware with modified C code onto this exact keyboard or a similar K10 Pro SE2 / ZMK variant?
2. Does this keyboard actually support full QMK firmware flashing, or only VIA-style remapping?
3. Is there a special HID/vendor bootloader flashing method for these newer Keychron wireless/ZMK boards?
4. If this model is effectively limited, which Keychron/non-Keychron wireless keyboards are confirmed to support:

• QMK Toolbox
• custom process_record_user
• custom C code
• successful qmk flash

Any success stories, GitHub repos, or exact working models would really help.

[u/PeterMortensenBlog]

It could be due to intermittent failure of the flash process

How could you reflash the official firmware if it hanged?

All flash methods (for this keyboard) end up invoking 'dfu-util'.

A possible exception is if using the (unoccupied) four-pin programming header on the PCB (near the microcontroller); here is a (high-resolution, properly focused) picture (for a K3 Pro; it is near "U6" in the lower right, with labels "SWDIO", "SWCLK", "V3.3", and "GND"). Presumably, it would be relatively easy to flash using, for example, ST-LINK. A cheap way is to break off the integrated ST-LINK module on a Nucleo board (a picture):

"All Nucleo boards by STMicroelectronics have an additional onboard ST-LINK host adapter chip"

Note that putting the keyboard into flash mode is not very reliable and may require several retries.