[coreboot] [PATCH] Halt TCO timer on Intel 3100 chipset

Ed Swierk eswierk at arastra.com
Sun Mar 30 08:30:20 CEST 2008

On Sat, Mar 29, 2008 at 5:20 PM,  <joe at smittys.pointclark.net> wrote:
> After thinking about it.....
> What are the advantages of disabling the TCO timer (besides
> rebooting)? Doesn't the system need this to run properly? By setting
> the no reboot the timer is still running....does it need to be?

The point of the TCO timer is to let a system recover automatically by
sending an interrupt and then rebooting if the OS crashes. While
operating systems can crash for all sorts of reasons, coreboot code
doesn't generally crash unless there's a hardware failure or
misconfiguration that will not correct itself by rebooting. Thus it
makes sense to disable the timer in coreboot and let a TCO-aware
payload re-enable it.

The TCO timer has no other purpose that I'm aware of, so it doesn't
matter whether coreboot neuters its effect by setting NO_REBOOT or
halts it completely by setting TCO_TMR_HALT. Leaving the timer running
still causes an interrupt to occur on timeout, but I think it's a
no-op unless the OS is paying attention.

This document explains the TCO timer in more detail:


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