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The DSMs each have a GPS with a pulse-per-second signal. Using NTP reference clock software, each DSM is then a stratum 1 time server. NTP NTP on the DSM uses the GPS reference clock to adjust the CPU system clock, and generally reports that their system clocks have the GPS reference clock has less than a 50 micro-second offset from the times of the GPS PPS signalsystem clock.
To query the system clock on a tower DSM from flux, use the ntpq -p command, for example 50m:
ntpq -p 50m
remote refid st t when poll reach delay offset jitter
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LOCAL(0) .LOCL. 10 l 20d 64 0 0.000 0.000 0.000
oGPS_NMEA(0) .GPS. 0 l 5 16 377 0.000 -0.001 0.031
The above shows the system GPS reference clock is offset from the GPS system CPU clock by -0.001 milliseconds. The "reach" value for GPS_NMEA should be 377 (octal value of all 1's). The reach for the LOCAL clock is always 0.
flux is configured to use all 6 DSMs as network time servers. flux runs , using chrony, a NTP client. To display the current chrony status, use chronyc sources:
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The above shows that the clock on flux agrees to within a maximum 52 microseconds with each DSM, as indicated by the "Last sample" value in brackets, which is the last calculated offset of the reference clock (in this case the DSM) from the system time on flux. A positive offset means the reference clock is ahead of the system clock.
The second character, under "S" should be '*' (indicating chrony on flux is sync'd to this server) or '+' (good server). Sometimes I've seen You may also see '-' (lately recently on 100m for some reason) indicating chrony does not have a high opinion of its time information, relative to the others.
The "reach" values should again be 377. If not, it means the DSM is not on the network, or its NTP server is not responding or sync'd to its GPS.
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