I’m using an Arduino Micro as controller for a keyboard and I want it to be useable during boot, in the BIOS etc. Unfortunately it looks like Arduinio’s USB/HID implementation does not support the boot (legacy) protocol which seems to be required for that. I’ve tried to figure out which changes are necessary for the boot protocol but I can’t really make sense of the specification (what exactly is the difference compared to normal USB HID Keyboards?).
Can somebody point me in the right direction or does anyone have a working implementation I could look at?