As per my other post, the keyboard is most likely a PS2 keyboard interface (physical or emulated) connected to a simple PS2/LPC(ISA) bus interface inside the EC. It will literally deliver an IRQ to that bus (IRQ 1) at which point the EC has to suck down a character from the keyboard buffer and do something with it.

It's not clever, can't use DMA and generally is the dumbest thing in the entire machine.

If they somehow manage to work around it I'd eat a box of lightbulbs. It's hard enough to coerce it to work to start with.

Source: I used to design embedded PC kit from the board level.