-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 2005-12-28, Komka Péter <[EMAIL PROTECTED]> wrote: > (If anyone cares:) > I guess that NTP's time, calculated from NMEA stamps, may be off by 1 or 2 > seconds. > > As I know, 1 or 2 seconds have to be added to the stamp's time to obtain > current time. Because it took some (not negligable) time to > - compute the time (in the GPS receiver) (known as "position fix calculation") > - tranfer the stamp to me. > (Millisecond part may be separately set via PPS.) > > I had done so calculation in my own software, and checked it against > independend time source. (Matched.) > > In the ntp source, so far I have not found such second-ajdustment. > This is why I wonder if it could give the precious time. > (I have not tested its time yet.) (No ntp-compiling experience (PC, Win).) > In general, any GPS receiver that it used in timekeeping needs to provide the PPS signal for use by NTP. It operates in a manner similar to the radio voice time announcements:
"At the tone, the time will be xx:xx" The GPS receiver sends the timestamp message for the next PPS pulse and the NTP software uses the exact time of the pulse to synchronize the local clock. The "position fix calculation" message has nothing in common with a GPS receiver used for timekeeping. The NTP NMEA clock type turns off all position messages and only enables the ones that are related to timekeeping. Tom - -- Public Keys: PGP KeyID = 0x5F22FDC1 GnuPG KeyID = 0x620836CF -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2 (FreeBSD) iD8DBQFDs8/E6/+C1GIINs8RAgtjAKC/pJ2bzm6R79Mo3yYWNQkz+0hoOACfaDVD 7FAmR/rcq/AAzySL6nEjn5Y= =SxY1 -----END PGP SIGNATURE----- _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
