Gpsd+chrony scheme always has 1 second error

GPS+PPS assigns time to Xavier system, using gpsd+chrony scheme, there is always a 1 second error. Cause and solution?

Do you mean 1 second shift?

Yes. The structure is GPS+PPS in hardware environment provides time information to Xavier system through software configuration using gpsd+chrony general scheme.

Could you give more information about GPS+PPS and how to check the error.

GPS+PPS connection method like this:

  1. hardware default connection:

    121pin wiring harness RS232-1 <------> GPS GPRMC
    121pin wiring harness PIN23 <------> GPS PPS

  2. software default configuration:

    $ sudo vi /etc/default/gpsd
    uncomment the line below in the file:
    # DEVICES="/dev/ttyTHS0 /dev/pps0"

  3. confirm services and gps:

    $ sudo systemctl is-active gpsd
    output “active” is ok.

    $ sudo systemctl is-active chrony
    output “active” is ok.

    $ gpsmon

and then compare the time from “gpsmon” and the time from website “https://time.is/
then GPS time always changes before time.is, about 1 second.

chrony.conf (1.8 KB)
and attached file is ‘chrony’ configuration file.

Hi @Ecotron.ai

In case you did not solve this yet, in your chrony config, you are defining that the PPS signal is arriving ~1 second delayed.

refclock SHM 0 poll -2 refid GPS precision 1e-1 offset 0.9999 delay 0.2

Try removing the offset:

refclock SHM 0 poll -2 refid GPS precision 1e-1 delay 0.2

Be careful with the delay value aswell.

Reference (chrony – chrony.conf(5)):
offset
This option can be used to compensate for a constant error. The specified offset (in seconds) is applied to all samples produced by the reference clock. The default is 0.0.

delay
This option sets the NTP delay of the source (in seconds). Half of this value is included in the maximum assumed error which is used in the source selection algorithm. Increasing the delay is useful to avoid having no majority in the source selection or to make it prefer other sources. The default is 1e-9 (1 nanosecond).

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