Linux Zeitsynchronisation mit GPS
Aus Port23Wiki
- https://austinsnerdythings.com/2021/09/29/millisecond-accurate-chrony-ntp-with-a-usb-gps-for-12-usd/
- https://austinsnerdythings.com/2021/04/19/microsecond-accurate-ntp-with-a-raspberry-pi-and-pps-gps/
Fedora Linux
USB GPS Empfänger:
lsusb Bus 005 Device 003: ID 1546:01a8 U-Blox AG [u-blox 8]
GPS Daemon installieren:
gpsd-3.23.1-2.fc36.x86_64
Datei /etc/sysconfig/gpsd anpassen:
cat /etc/sysconfig/gpsd # Options for gpsd, including serial devices OPTIONS="" # Set to 'true' to add USB devices automatically via udev USBAUTO="true" # # DEVICES="/dev/ttyACM0" GPSD_OPTIONS="-n"
Kommando aufrufen:
gpsctl -n # setzt den Ausgabe Modus / turn NMEA output on or off
Gpsmon aufrufen und Funktion/Empfang prüfen:
gpsmon gpsmon 127.0.0.1:2947
Datei /etc/chrony.conf anpassen:
/etc/chrony.conf refclock SHM 0 refid NMEA offset 0.040 # offset erforderlich; Abgleich mit gutem NTP Server (z. B. PTB)
Grund:
- https://www.lammertbies.nl/comm/info/gps-time
- Although the clock inside the receiver itself runs with an accuracy of some nanoseconds, the transfer of the data to the computer causes such a large delay, that in practice it is not possible to synchronize the clock of the local computer with that signal with an accuracy of better than a handful of milliseconds.
GPS receiver mit "noselect" in u. a. Ausgabe deaktiviert:
# chronyc sources MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== #? NMEA 0 4 377 23 -328us[ -328us] +/- 164us ^* ntp.netnod.se 1 10 377 1004 -1285us[-1263us] +/- 18ms ^+ any.time.nl 2 10 377 25 -316us[ -316us] +/- 22ms ^+ ntp3.lrz.de 1 10 377 93 +4330us[+4330us] +/- 34ms
Hinweise auf https://austinsnerdythings.com/2021/09/29/millisecond-accurate-chrony-ntp-with-a-usb-gps-for-12-usd/ beachten.
