[time-nuts] pc clock crystal long term variations
phk at phk.freebsd.dk
Sun Aug 8 21:40:35 UTC 2010
In message <20100808230143.2285e822.attila at kinali.ch>, Attila Kinali writes:
>What surprises me though is the stability of the crystal.
>In the months between reboots, there is less than +-1ppm variation,
>The machine is a 16y old DEC PC, which has been used as a desktop
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
They had a few machines that could slot either x86 of alpha CPU
boards, and they were built from very high quality parts.
>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.
Check your syslog/dmesg for the frequency estimate and you can see
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