================
> > From: Gregory Poudrel <chojin at chojin.info>
> > I recently had some problems with my ASUS P5A motherboard (K6-II 350) on
> > FreeBSD 5.2-RELEASE.
> > In fact, I had GENERIC kernel installed and ACPI activated.
> >
> > First problem:
> > Time flow was incorrect. In fact, 1 second meaned 0.5 second for FreeBSD.
> > Each minute I tested a ntpdate and there was 76 seconds difference.
> > When I rebooted and check in BIOS, time was correct and flowed independently.
>
> This is a known bug in the P5A. It's ACPI-Safe clock is broken and runs
> at double speed.

If that is the only problem with it, then it is easy to fix by telling
it what its actual speed is (sysctl machdep.acpi_timer_freq=whatever).
This can be done automatically by calibrating the frequency relative to
any non-broken clock with a known frequency, as is done for the TSC
timecounter.

> Use the TSC clock by putting the line:
> kern.timecounter.hardware=TSC
> into /etc/sysctl.conf.

But using the TSC is better anyway, since it has a higher quality than the
acpi timer if thermal control mechanisms are not used (usually the same
accuracy, and always a lower overhead).
==========================================================================
[503] Thu 30.Dec.2004 16:51:10 [kadmin at archangel][~]
#sysctl kern.timecounter.choice
kern.timecounter.choice: TSC(800) ACPI-fast(1000) i8254(0) dummy(-1000000)

Last box I had trouble like this on was K6-2/500 on Asus p5a mobo.
Setting to i8254 worked in that case. If you've not tried all the
possibilities, do so now.