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From: chris@umcp-cs.UUCP
Newsgroups: net.unix-wizards
Subject: Re: 4.3 hangs
Message-ID: <2887@umcp-cs.UUCP>
Date: Sun, 10-Aug-86 01:32:36 EDT
Article-I.D.: umcp-cs.2887
Posted: Sun Aug 10 01:32:36 1986
Date-Received: Mon, 11-Aug-86 04:38:07 EDT
References: <2836@brl-smoke.ARPA>
Reply-To: chris@umcp-cs.UUCP (Chris Torek)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 36

In article <2836@brl-smoke.ARPA> dlu%tektools.tek.csnet@CSNET-RELAY.arpa writes:
>The problem you describe has not shown up, to my recolection, on the
>785 here.  But I do know how to get a dump from the console [...] :
>
>	^P
>	HALT
>	START <address of doadump()>

This does indeed provide a crash dump.  However, it is almost always
preferable to force an actual crash:

	^P
	H
	D PC -1		! N.B.: `@crash' does these three commands for you
	D PSL -1	! (and perhaps the HALT as well).  But this works
	CO		! even if you have no file `crash' on your floppy.

or, on a 750,

	D/G F FFFFFFFF
	D P FFFFFFFF
	C

This invalidates the PC, sets the PSL to kernel mode, IPL 31, and
continues, causing an immediate trap and a `panic: Segmentation
fault'.  The advantage this has over simply starting the CPU at
doadump() is that disk buffers are written, leaving the file systems
in a much more recoverable state.

(On the other hand, sometimes the disk syncing leads to another
hang.  A second trap invokes a crash dump without attempting to
sync, so you still need not know the address of doadump().)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1516)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu