[ntp:questions] Drift from serial activity, VIA system, LInux

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Sun Jun 8 02:03:36 UTC 2008

I'm setting up a small system to monitor things like line voltage
and temperature.

It uses a serial connection to a UPS box to get the line voltage.

The quirk is that the drift changes when I run the monitoring
program.  It changes more if I poll faster.  It changed by
20 ppm when I was polling with a 10 ms delay and it's more
than 80 ppm and still climbing when I reduced the delay to 1 ms.

I let it run for a few days in the 20 ppm mode.  The drift was stable,
just like it was before I turned on the monitoring code.  I can see
it track the daily temperature changes.

The system is a VIA C7 CPU with a VT3314 chipset running
a 2.6.25 kernel.  The kernel sources are stock but the
configuration options are my own.

Has anybody seen anything like this?  Any suggestions on where
I should look for more info and/or to track this down?

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