VIA system freezing since upgrade to wheezy

[Mark Carroll <mtbc@ixod.org>]

I have a small low-power mini-ITX system that I use as our home router.
It is VIA C7 based with VIA CN700, VT8237, etc. on the motherboard.
Mainly it just sits there moving packets through iptables, via RTL-8139
and VT6102 (Rhine) ethernet cards. There's other hardware, of course,
like the S3 UniChrome Pro graphics, that I don't exactly exercise.

Under squeeze it used to be rock solid. Last week I upgraded it to
wheezy, also from a custom 2.6.26 kernel to the stock Debian
3.2.0-4-686-pae image. Since then, it's frozen a couple of times.
Nothing useful is left in the logs afterward.

Is this some known problem? Is there anything I should be doing to help
to diagnose it? I've looked through the kernel startup messages but I
don't see anything worse than,
	Marking TSC unstable due to TSC halts in idle
        longhaul: APIC detected. Longhaul is currently broken in this configuration.

I had wondered if it is possible that this Longhaul issue is making the
system run rather hotter than necessary, but running a for(;;) loop in C
makes the "sensors" output temperature increase without freezing the
system.

-- Mark