Good idea.  I think it is useful to attempt shared drivers (and
shared modules in general) as long as the amount of shared code
is large compared with the amount of non-shared code.  It sounds
like the machine-dependent `millicode' would be relatively small.

The only places where I've seen this lead to a mess is where the
author worked "too hard" to try to share little bits of code, and
ended up with lots of complication in trade for rather small gains.

Gordon