Re: Catching NForce2 lockup with NMI watchdog

[Richard B. Johnson]

On Tue, 16 Dec 2003, Maciej W. Rozycki wrote:

> On Mon, 15 Dec 2003, George Anzinger wrote:
>
> > >  Hmm, you could have simply asked... ;-)  Anyway, an inclusion is doable,
> > > I guess.
> >
> > I suspect I did, but most likey the wrong place.  In any case, I would like to
> > think that "read the source, Luke" is the right answer.
>
>  Certainly it is, but not necessarily the only one. ;-)
>
> > So, while I am in the asking mode, is there a simple way to turn off the PIT
> > interrupt without changing the PIT program?  I would like a way to stop the
> > interrupts AND also stop the NMIs that it generates for the watchdog.  I suspect
> > that this is a bit more complex that it would appear, due to how its wired.
>
>  Well, in PC/AT compatible implementations, the counter #0 of the PIT has
> its gate hardwired to active, so you cannot mask the PIT output itself.
> So the only other choices are either reprogramming the counter to a mode
> that won't cause periodic triggers (which is probably the easiest way, but
> you don't want to do that for some purpose, right?) or reprogramming
> interrupt controllers not to accept interrupts arriving from the PIT.
>
>  Note that Linux may behave strangely then. ;-)
>

Masking OFF the timer channel 0 in the interrupt controller
is probably the easiest thing to do. The port is read-write,
and the OCW default to having it accessible.

	movw	$0x21, %dx	# Controller 0, mask register
	inb	%dx, %al	# Get mask
	orb	$1, %al		# Mask off bit 0
	outb	%al, %dx	# Write it back

You can reenable by:

	movw	$0x21, %dx
	inb	%dx, %al
	andb	$~1, %al
	outb	%al, %dx

With port numbers less that 256, you actually don't need the
DX register but I forget if the AT&T assembler needs a $ before
the port number when doing this.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.22 on an i686 machine (797.90 BogoMips).
            Note 96.31% of all statistics are fiction.


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