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.
But one question remains: how does the EC control stuff like the bluetooth radio and webcams? They're USB devices to the OS, so in theory there should be a USB hub inside the EC?
Not necessarily. It may only have power control function. If you pull a USB device out it's the same as turning it off in theory and vice versa. It's probably just turning the device off or setting it into standby mode.
edit to add: some Intel south bridges have integrated EC which makes things a little uncertain.
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.