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Date: Sun, 2 Jul 1995 14:50:28 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199507020450.OAA32661@godzilla.zeta.org.au>
To: hackers@freebsd.org, matt@lkg.dec.com
Subject: Re: Best way to diagnose system lockups?
Sender: hackers-owner@freebsd.org
Precedence: bulk

>When the system locks up, neither DDB (via CTRL/ALT/ESC) nor hardclock
>(no watchdog panic fires) is called.  The only way back is reset which
>of course doesn't result in any useful information.  (damn it!  I like
>machines with halt buttons (like a VAX or an Alpha).  Sigh)

I Ctrl-Alt-Esc doesn't work, then the system must be wedged at spltty
or splclock (unfortunately splimp is higher than spltty if slip or ppp
is configured, so wedging at splimp makes it difficult to enter ddb).
I usually remove the keyboard bit (1<<1) from tty_imask to debug wedging
at spltty.  This is perfectly safe if you don't touch the keyboard and
fairly safe (perhaps perfectly safe) even if you do (the keyboard intr
handler sets the bit although spltty() doesn't).

Bruce