PS/2 Driver

[thejpster]

We need a generic PS/2 driver that works on GPIO pins and interrupts. We can then stand up two of them - one for keyboard, one for mouse.

[thejpster]

Requires #6 so the devices get power

[thejpster]

Note that pins must be inputs floating whilst the DC PSU is off, to avoid back-powering the PS/2 device.

[thejpster]

#17 brings in pc-keyboard. This might need splitting into a generic PS/2 transport, and then a keyboard decoder.

[thejpster]

This is a good guide to how the PC keyboard controller works.

https://www.win.tue.nl/~aeb/linux/kbd/scancodes-11.html#ss11.1

[thejpster]

Keyboard reads work but need write support to alter LEDs and also to turn the mouse on.

[thejpster]

Also consider turning off PS/2 port when we're busy