Machine check, type 0 (VAX 780)

[Jesse Fred Shumway]

> > Does anyone know what 'Machine check, type 0' is on a VAX 780?
> > The message also says 'CP read timeout fault' and prints some
> > registers, but I can't find any documentation around here that
> > describes things like that. We have goten four of them since
> 
> This problem is caused by a device on the Unibus.
> It occurrs when a device fails to reply with its vector address when requested
> so during a bus-request/bus-grant protocol.  This can be a tough problem
> to isolate.  I know of no proceedure to find the culprit except by
> replacing one board at a time.
> 
> It is a hardware problem.


Yes, it is definitely a hardware problem. UNIX simply takes a
microcode machine check interrupt and prints several of the
privileged machine registers.

I don't want to be argumentative, but, I've never seen this
problem's locus to be a UNIBUS device. Usually, focusing on the
memory subsystem seems to effectively isolate the offending board.
Although, on one machine I know of DEC resorted to replacing the
SBI backplane in their attempts to get rid of these errors;  which
regrettably returned the following spring with the temperature
fluctuations that accompanied the annual air conditioning
shakedown.

Quoting from DEC's "VAX Maintenance Handbook", 1983 edition, EK-
VAXV2-HB-002; "CP refers to memory references explicitly requested
by microcode and whose address comes from VA". VA is the
microcode's virtual address register. While you're at it, get your
self a copy of the "UNIX System V Release 2, Error Message
Reference Manual, DEC Processors", 307-114 issue 2, from your AT&T
UNIX sales rep. With it, and a copy of the VAX processor register
layouts you can get a good feel for how the hardware is
misbehaving. Its really nice to graciously forgo the handwaving a
VAX maintenance person often delivers when asked, "Ah-gee, any
idea what's wrong?".  No? :-)

Jesse Fred Shumway	AT&T 	ihnp4!ih1ap!jfs	  (312) 510-7880