pmax driver, to be diffable with the NetBSD Alpha driver. Specifically,
the pmax driver now uses register names dev/ic/z8530.h. The driver now
uses new-style config and dynamically-allocated softc structures. The
driver no longer resets the "other" channel on an SCC when changing tty
parameters. The #ifdef'ing away of processing of the output clist for
non-console lines is no longer done. (Non-console serial ttys might even
work now.) Other discrepancies between the pmax and alpha drivers, which I
don't understand yet, are marked by XXXes.
The 4.4bsd pmax console redirection code is still present, protected
by #ifdef TK_NOTYET. Diffs from the Alpha scc driver are now minimal.
Verified to boot on a Decstation 5k/240.
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