Version vom 11. Februar 2024, 12:20 Uhr

• 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.

Hinweise auf https://austinsnerdythings.com/2021/09/29/millisecond-accurate-chrony-ntp-with-a-usb-gps-for-12-usd/ beachten.