I've put a shar of my latest scn driver up for ftp from
alpha.gnu.ai.mit.edu:/budne/pc532/scn.shar.gz.  It now works (doesn't
hang your machine) under 1.1alpha, and uses "soft" interrupts to
retrieve characters stored by the RxRDY ISR;

    magrathea# vmstat -i
    hardware interrupts:
    interrupt       total     rate
    clock          482354      100
    ncr0            22631        4
>>  scnrx           54746       11
    scn            163333       33
    Total          723064      149

    software interrupts:
    interrupt       total     rate
    softclock        2393        0
    softnet            26        0
>>  scnsoft         54626       11
    ncr0            17469        3
    Total           74514       15

The driver is still untuned, and has a bug which is tickled by csh in
"filec" mode, or anything that uses echo & cbreak (ie; tcsh gdb) --
CRLF echo is busted. I've also added a baud table entry for 115.2, but
it's unclear how well it will work (I have no means to test it)!

It's not for the faint of heart, but then I'm running with the "ncr"
(rather than "oldncr") scsi driver!

-phil