max TR level on UNIX

[Gregory M. Paris]

We have recently connected an SI 9753 tri-density tape drive to
two of our VAX 11/780's running 4.2BSD.  Switch the rocker switch
to connect to either machine then power up and voila, the VAX
hangs with "too many zero vectors."

One of people at SI's California office tells us that this happens
because we have the tape drive connected to TR 12 (on both machines).
He claims that UNIX cannot handle TR interrupt levels above 11.
We tried running VMS on one of the VAX'es and it was able to
access the drive successfully.  Later this week we are going to
reconnect the drive at TR 10 for experimentation, but we won't be
able to leave it that way.

Does anyone know whether or not this really is a UNIX limitation?
Does anyone have a fix for it?  Please respond by mail and I'll
summarize replies to the net.  Thanks!
-- 

++--------------------------------------------------------------------------++
||  Gregory M. Paris                                                        ||
||                    ...!{allegra,linus,raybed2,ccice5,brunix}!rayssd!gmp  ||
++--------------------------------------------------------------------------++