scw@NetBSD.org said:
> I notice Synaptics do a combined stick/pad, so perhaps they already
> have  the relevant documentation up on the developer's section of
> their  website.

They have an extension to the keyboard controller protocol so
that it can handle 4 "aux" ports individually.
The BIOS (either a special firmware of the KBC or some SMM
tricks) will hide this from the OS (this means select one, or
multiplex) unless a special command is sent to the KBC.
I once looked into this because I've got a Dell laptop with
both pad and stick... I left it alone finally because the
"pckbcport" driver interface needs a rework to deal with this,
and I don't have access to a machine using "pckbcport" w/o an
ISA KBC for testing.

best regards
Matthias