Keyboard Controller

While the SBC3 can have a PS/2 keyboard connected, it's by way of one of the serial ports, so by the time we see keys, they've been converted from key press/key release events. This is usually a "good thing"™️ but there are times when having the raw data would be useful.

I'll write a new firmware for the ATMega328 which allows both, defaulting to the current behaviour but allowing raw mode to be enabled by sending some crazy sequence to the ATMega device.