On 2009-12-30, Hal Murray <hal-use...@ip-64-139-1-69.sjc.megapath.net> wrote: > In article <slrnhjkta6.4e4.un...@wormhole.physics.ubc.ca>, > unruh <un...@wormhole.physics.ubc.ca> writes: >>ntpd has suddenly broken out into oscillations. it is fed by a Garmin >>18 LVC PPS via shm. The oscillation has a period of just under an hour ( >>about 50 min) and an amplitude of about 10usec. in the offsets ( >>amplitude of about .005PPM in the rate). Since this is acting as the >>clock for a number of other machines, they are also showing the >>oscillation especially in the rate. >>While I suppose this could be something in the GPS itself, it looks more >>like an oscillation in ntpd. >>Nothing changed when the oscillations started. Ntpd had been started >>on Dec 14, and this change began on Dec24. >>You can see the graph on www.theory.physics.ubc.ca/chrony/chrony.html , >>the graph for the machine called string. >> >>Has anyone else ever seen this kind of thing? > > What OS? (version?)
Linux-- Mandriva 2008.1 ( kernel 2.6.24.7-desktop-3mnb) This oscillation has just started. > > What is the temperature like? The temp should be relatively stable ( certainly no air conditioner, although possibly cooler than usual because the heating has been turned down for the Christmas break-- After all nothing happens in the University during Christmas. Research-- what's that?. HOwever it so happens that I have the internal temp recorded via lmsensors for the past 5 days, and there is some evidence of a one degree flucutation (the resolution of the onboard thermometers) with about the same period. No idea what that is, since there is no airconditioning/heating. But I suppose it could be causing that fluctuation in the rate and thus the offset. Which somehow started on Dec 24. Lets see what happens when classes begin again next week. > > If you feed a sawtooth into a PLL, the offset will be the derivative, > a square wave. The amplitude of the square wave is smaller with > higher gain. A sawtooth with a 1 hour period is possible from > air conditioners. Actually, no, the offset is the integral, not the derivative, of the drift, so the offset will be a bunch of peaks. > > > I've seen oscillations on boxes using the pool, or at least stuff > that looks like oscillations to my eyeball. That's on Linux. > (They have been "fixing" the timekeeping code. I wouldn't be > surprised by anything.) Yes, but then this "fix" whatever it is, has been the same for months now. > _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions