Has anyone ever given any thought to abstracting out the parallel port
interface so it could be used as a general-purpose I/O port, instead of
just an output port?

It seems that there are a lot of devices that use the parallel port for
input and output, and it might be useful to be able to talk to these
devices without having to write a special driver for each one.  I'm not
sure if that's 100% feasible, as I suspect that all these different devices
in question probably use different ways of communicating via the parallel
port.

Why do I ask?  I've found a place that makes a oscilloscope which you can
attach to a parallel port for $400.  For another $100, they'll sell you the
source code to the front-end program (which is in Visual Basic, unfortunately).
Admittedly, it's not a _great_ oscilloscope (only 1MHz analog bandwidth), but 
a digital scope for $500 would be awesome.  Even more awesome would be if
I could use it to debug my HC11 boards from NetBSD (since I already have the
complete NetBSD cross-compilation environment for the HC11).

Something else I've been wondering about - on the different architectures
that NetBSD supports and that have parallel ports, what kind of hardware
interface do the parallel ports have?  Are they the same sort of IC that
the i386 has, or are they something completely different?  Obviously, it
would be a good idea to have the hypothetical abstract parallel port
driver work on all architectures NetBSD supports.

--Ken