On 2010-03-11, Richard B. Gilbert <rgilber...@comcast.net> wrote: > David J Taylor wrote: >> "Miroslav Lichvar" <mlich...@redhat.com> wrote in message >> news:20100311124036.ga22...@localhost... >> [] >>> I did a NTP vs chrony comparison last June with GPS 18x LVC in an >>> office environment, clock drift was moving in about 0.8ppm range. Here >>> are distributions of PPS samples received from gpsd: >>> >>> http://fedorapeople.org/~mlichvar/chrony/chrony_vs_ntp.png >>> >>> With recent chrony, NTP and kernel versions the results might be >>> different though. >>> >>> -- >>> Miroslav Lichvar >> >> Miroslav, >> >> Thanks for that, a most interesting comparison, and thanks to everyone >> for their input. >> >> I've recently switched the old (2005) FreeBSD system back on, to see how >> well in performs in my own environment. From what's been said, I rather >> suspect that were I to go for a more modern, faster, Intel Atom system, >> any improvement in accuracy I might get could be swamped by the >> temperature changes in the room. >> >> There's also, I will admit, a slight doubt about the effort involved for >> the benefit to be gained. With Windows, I am quite happy, and >> configuring, using or testing NTP is no problem. With FreeBSD is seems >> that the old PPS atom driver has gone, and I may need to configure yet >> another driver - gpsd. The number of variants of Linux doesn't help - I >> only need a command-line or Telnet interface. And remembering how long >> it took to recompile the kernel last time, and the amount of help I >> needed to know how to do that, also fills me with doubt. >> >> So I suspect that the performance I'm now seeing from Windows (well >> within 100us) may well be "good enough" for me. Perhaps if I get more >> free time, and a little more income this year, I may get a >> paperback-sized Intel Atom box and see how it does. At least some do >> have serial ports! And I would be most interested to hear of anyone who >> does configure such a device. >> >> Cheers, >> David > > 100 microseconds is pretty good. Getting the time *into* a computer > takes time and the time taken is not easy to measure.
Considering that chrony can give sub microsecond resolution from say a GPS source, ( and ntpd 2usec) 100usec is good only only in a certain defintion of good. Getting the time into the computer from a refclock is on the 1usec level ( measured), certainly not 100usec. _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
