Maybe let the clocks run unadjusted all day and resync between fixed times once a day? This is what the power companies do. You can back-figure the precise times if you really need to from the once a day correction files.
This assumes the clock rates are just off a bit, and do not randomly fluctuate. -John =============== > I'm looking for a good (short) description and/or a generalized model for > relating a local time counter to some external reference. Here's the > scenario.. > A computer has a local clock that is a counter being driven by a local > oscillator. > Periodically, we get "time updates" from some outside source that give an > "absolute time" and a sync. > > We need to use "calibrated time" to record log files and schedule events. > > A simple way to relate local counter to absolute time is: > Calibrated time = (local counter / counter rate estimate) + time offset. > > Calculating the rate estimate from (local counter at time B - local > counter at time A) / (absolute time at time B - absolute time at time A) > And offset in a similar way. > > But this has the problem that the "calibrated time" might have > discontinuities. Especially if you change the rate estimate and offset in > a step function. Calibrated time might even go backwards. > > I guess an additional requirement on "Calibrated time" is that it be > continuous and monotonically increasing. I can see that one can get this > by "gradually" adjusting the rate estimate and offset (i.e. if your local > clock runs fast so your local calibrated time has gotten ahead of absolute > time, you set the rate lower than the true rate until it has slipped back > fast and then slowly bring the rate back to the true rate) > > And this works pretty well if the outside reference is "better" than my > local clock (and is essentially what NTP does, right?), but what if the > reverse is true. > Consider if my local clock is high quality, but I have to discipline > Calibrated Time to an outside time that is of much poorer quality. (By > the gods, it's 6AM when the sun rises and 6PM when the sun sets, so make > everything adjust to fit that, and don't give me grief about seasonal > variations in sunrise/set times). > > What's a good way to do this, hopefully that allows later reconstruction > of what the history of transformations was (e.g. I should be able to take > my calibrated time, and convert it back into local counter time, by using > the log of changes in model parameters). > > Thanks for ideas and pointers in advance > Jim > > > > > > James Lux, P.E. > Task Manager, SOMD Software Defined Radios > Flight Communications Systems Section > Jet Propulsion Laboratory > 4800 Oak Grove Drive, Mail Stop 161-213 > Pasadena, CA, 91109 > +1(818)354-2075 phone > +1(818)393-6875 fax > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.