Can be flashed with avrdude like this:
avrdude.exe -C avrdude.conf -P COM3 -c wiring -p m2560 -b 115200 -U ../custom-a20t-btt3in1-firmware.hex
Can be flashed with avrdude like this:
avrdude.exe -C avrdude.conf -P COM3 -c wiring -p m2560 -b 115200 -U ../custom-a20t-btt3in1-firmware.hex