This is the Corne v4(rev4) firmware guide.
Please check the pcb version v4.0.0 or v4.1.0 first.
After that, download the firmware of VIA/Vial from below.
standard (3x6) v4.0.0
mini (3x5) v4.0.0
standard (3x6) v4.1.0
mini (3x5) v4.1.0
Connect to the PC while holding down the BOOT button, or while connected to the PC, hold down the BOOT button and press the RESET button. After that, an RPI-PR2 device will be mounted.
Drop the downloaded uf2 file into the RPI-PR2 device to complete flash.
Once the firmware has been written to one side, follow the same procedure for the other side.
Please refer to https://github.com/foostan/kbd_firmware.
VIA can be used by flashing the firmware for VIA.
If you use Corne v4, please download json file from bellow and load at VIA(You need to enable Design tab at the config page)
Vial can be used by flashing the firmware for Vial.