On Monday, 16 September 2013 08:00:09 UTC+1, Igor Pavlov wrote: > Hi! > > > > I am using GPS-receiver based on Geos-1m chip ( > > http://www.geostar-navigation.com/en/navigation_05.html) > > > > I connected it to serial port and configured NTP. > > It becomes unused by NTP: when do ntpq -p reuest ti puts "x" near > > "GPS_NMEA(1)" record. > > > > What reasons can be for this? > > > > Example of "ntpq -p" output > > > > remote refid st t when poll reach delay offset > > jitter > > ============================================================================== > > xGPS_NMEA(1) .GPS. 0 l 14 16 377 0.000 -303.07 > > 4.292 > > *stratum1.net .PPS. 1 u 62 64 377 62.800 -68.052 > > 43.693 > > +dl120g7.naviteh 194.190.168.1 2 u 58 64 377 30.151 -100.04 > > 52.432 > > +89.221.207.113 192.36.133.25 2 u - 64 377 10.006 -105.88 > > 64.279 > > > > > > -- > > Igor Pavlov
We find that the problem with many (not all) NMEA GPS receivers is that often too much data is transmitted between each PPS output. This can have the effect that the time output (ZDA) sentence can occasionally shift either side of its corresponding pulse output. This has the effect of a 1 second offset occasionally being added to time stamps supplied to the NTP daemon. Sometimes, increasing the baud rate from the standard 4800 bps to 9600 or even 19200 bps can help by allowing more characters (data) to be transmitted between each 1PPS output. Also, as previously mentioned, simply feeding a 3.3V or 5V pps output from a GPS receiver into a RS232 port will not work as the voltage levels are different. You will need a simple TTL logic to RS232 converter such as a MAX232 device to convert the PPS output signal to the correct voltage level. Andy Everett TimeTools GPS-Referenced NTP Servers http://www.timetoolsglobal.com/information/gps-ntp-network-sync-products/ _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
