David Woolley schrieb: > Heiko Gerstung wrote: >> local NTP servers. On our time server appliances we use minpoll 4 >> maxpoll 4 for talking to the integrated refclock (GPS, MSF, DCF77 or >> IRIG) and this dramatically improves the reaction times of ntpd when it > > Dave Mills, you again need to note the "market" perception that ntpd has > poor transient responses. > >> comes to things like initial synchronization, reception outtages and >> so on. Although the parse driver (which we use for all our refclocks) > > As I understand it, maxpoll has rather limited impact. The most it may > do is speed up the detection of a phase hit. As I understand it setting > a low maxpoll simply causes oversampling of the data without actually > limiting the minimum filter bandwidth. I suspect that is why the > subsequent discussion only mentions minpoll.
For me maxpoll is an important parameter as well because ntpd switches to larger polling intervals pretty fast and for a lot of our customers it is important that ntpd recognizes as fast as possible if a GPS signal is lost or the GPS receiver/IRIG time code reader/AM radio looses sync for some other reason. They want the unit to switch as soon as possible to a fallback source which will take significantly longer with a polling interval of 64s when compared to 16s ... the same applies when the refclock recovers after becoming unsynchronized. >> To me there is no sense in only getting one sample in 64 seconds when >> your expensive and highly accurate hardware reference clock offers one >> very good sample every second. > Most highly accurate reference clocks do not produce high accuracy on > their NMEA output, but rather on their PPS one. ntpd only requires the > NMEA input to be good to a second, in that case. Yes, but in our case the parse driver utilizes the PPSAPI under Linux (as does the NMEA driver) which means that your refclock driver gets a measurement (based on the PPS) each second. Regards, Heiko _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
