Help wanted, Protection trap in dz.c (4.2)

[Geoff Whale]

Forgive me if this been has been aired before.  At random intervals
our 780 console says:

	trap type 9, code = 0, pc = xxxxxxxx
	panic: Protection fault

This message is repeated 3 or 4 times, after which we get

	?INT-STK INVLD
	HALTED AT .......

whereupon the machine picks itself up, dusts itself off and starts
all over again.  'xxxxxxxx' is in _dzrint, in the code:

	if(tp->t_line == NETLDISC) {
		c &= 0177;
		BKINPUT(c, tp); <--- a macro in bk.h
	} else
	......

We have a 780 running 4.2 with 56 lines of DZ and 16 lines of Emulex
CS21 (=DMF32).  We do run the bk discipline on a few of the DZ lines,
but not on any of the DMF's (although I can't be sure about the last 
part).  I'll be very grateful for any ideas on this one, please mail
me if you can help. (If you want any solutions I get, mail me and
I'll forward them.)
Regards,
geoff
-- 
Geoff Whale  ...seismo!mcvax!ukc!stc!idec!geoff