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From: aps@decwrl.UUCP (Armando P. Stettner)
Newsgroups: net.unix,net.unix-wizards
Subject: Re: Machine check, type 0 (VAX 780)
Message-ID: <282@decwrl.UUCP>
Date: Tue, 3-Sep-85 16:46:10 EDT
Article-I.D.: decwrl.282
Posted: Tue Sep  3 16:46:10 1985
Date-Received: Thu, 5-Sep-85 00:43:55 EDT
References: <204@drivax.UUCP> <1162@inuxc.UUCP>
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Organization: Digital Equipment Corp., Palo Alto, CA
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Xref: watmath net.unix:5557 net.unix-wizards:14693

> > 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
> > last Wed.
> > 
> > We are running 5.2.2 with 4M, one rm03 and one rp07.
> > -- 
> > 
> > Alan Fargusson.
> > 
> > { ihnp4, amdahl, mot }!drivax!alan
> 
> 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.
> 
> Another cause of this problem can be external wiring to a DR-11 interface
> (parallel i/o).  Noise on the request A or B lines can cause the DR11
> to withdraw in the middle of a bus-request/bus-grant protocol.
> 
> It is a hardware problem.

Hi there.
There may have been more information in Alan Fargusson's message
that I did not see but P McFerrin is wrong in saying that the problem
is a UNIBUS device.  Don't confuse "read timeout" with UNIBUS timeouts
(which are handled somewhat differently on VAX-11/780's than PDP-11's).
A "CP read timeout fault" is caused when the cpu tried to do a data
reference and the bus control logic could not gain access to the SBI
or it received no response for so many cycles (or the requested
location [nexus?] responded with Busy (or something to that affect)
for so many cycles).  

In the case of a failed UNIBUS access, the UBA will cause an interrupt
and in 4.2 (Ultrix-32), an error message will be printed, and the system
will attempt to reset the UBA.  System V's actions do not seem straight
forwart to me (but I only looked at it for about 10 min) but it appears
to print out the contents of some registers and then return.

This is not to say that there couldn't be a problem with Alan's UBA ...
	aps.