On Jan 21, 9:24 am, "Maarten Wiltink" <[email protected]> wrote: > <[email protected]> wrote in message > > news:[email protected]... > [...] > > > I'm trying to track the drift of my GPS clock RELATIVE to > > the clock that I would have obtained without GPS (and vice versa). > > If I understand you correctly, you want to generate a log with > two timestamps on each entry: one free-running, one GPS-synced. > > You could _not_ run NTP on your test machine, and whenever a message > is logged, fetch a timestamp from another machine that does run NTP. > Microsecond accuracy on that machine is not very hard with a GPS > clock, but getting it into the test machine with the same accuracy > may be a bit of a problem. It's mostly a matter of having the transfer > take about the same time each time; if a good timestamp always arrives > in exactly thirty milliseconds, that's good, you can correct for that. > > Another avenue is to run NTP on the test machine but not let it touch > the clock (or not let it believe the other NTP server or for that > matter any other server; you want a free-running clock). You still > need the GPS-synchronised other NTP server, but running NTP on the > test machine gives you easy, continuous, and fast access to an estimate > of the current error in the local, free-running clock, and thus an idea > of what the 'real' time is. > > > My final goal is to convert a series of gps timestamps to the > > equivalent unsychronized timestamps. > > Whereas I propose doing it the other way around. It produces the same > information and it's easier to do. I think. > > Groetjes, > Maarten Wiltink
Hi Marteen, I've done it (a log with two timestamps on each entry: one free- running, one GPS-synced) with a single machine and I think the results sound good. I've posted a new message which expains how I does it: "A practical implementation for tracking the drift of a GPS clock relative to a non steered clock (& the associated results)" see also http://www-phare.lip6.fr/~kezadri/temp/tstamp_conv.html Note that the non steered clock is the clock that the PC would have used if no GPS was installed. Regards Ryad _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
