[time-nuts] pc clock crystal long term variations

Attila Kinali attila at kinali.ch
Tue Aug 10 11:16:56 UTC 2010

On Sun, 08 Aug 2010 21:40:35 +0000
"Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:

> DEC used way better crystals than the average PC-HW producers, so
> I am not very surprised.  Not sure if this was just general good
> engineering or a panicy reaction to all the trouble the alphas
> gave them.
> They had a few machines that could slot either x86 of alpha CPU
> boards, and they were built from very high quality parts.

This machine is a quite "cheap" dual P-II 266 system. No way to
fit in Alpha CPUs. Though, there were Alpha machines in the same
case. I guess they must have used very expensive crystals back
then :-)
> >And why doesnt the
> >crystal relax back into it's old ppm value, but stays where it
> >is after a reboot/power cylce?
> You kernel tries to measure/estimate the crystal frequency at boot,
> it does not get the same value on every boot.

Do mean the BogoMIPS callculation of linux? I don't know of any
other timing dependend loop in there.

> Check your syslog/dmesg for the frequency estimate and you can see
> this clearly.

I will try to fit the BogoMIPS data over the ntp loopstats and see
what that yields.


			Attila Kinali

If you want to walk fast, walk alone.
If you want to walk far, walk together.
		-- African proverb

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