SPI microcontroller on Mac bus?

[Metrophage]

I am only waking up now and drinking my coffee, and possibly brainstorming nonsense, so please bear with me here for a moment.

I am not an OpenFirmware guru of any sort, but I recall looking through OF device tress before and seeing "SPI". Unless they are talking a completely different sort of SPI, I would guess this to refer to a Serial Peripheral Interface bus. Has anyone else here ever poked around their Mac's SPI? It would require knowing where four different lines are.

It could be handy for installing an ADB port on New World Macs for those of us who have lots of decent ADB input devices.