For what it may be worth, here are the current clock performance
measurements for the two stratum-1 time references on my home LAN. Each
computer has an AMD FX-8350 processor on an ASUS motherboard, with a DB9
serial header on the motherboard, and each system has a Garmin 18x
receiver wired to a DB9 serial connector.
The jitter (dispersion) in each case seems to be significantly less than
what I might expect from a USB-based connection. I don't have specifics
anymore, but I remember I tried connecting a Garmin 18x GPS to a PCIe
serial card once, and the result was way too unstable to provide any
sort of useful time reference. I assume this was because the PCIe
serial card was really just a serial interface to a USB chip, right?
Note that I'm using *chrony* here (not *ntp* or *ntpsec*).
(11/05 12:27:04 richw@equality ~ 2118) $ chronyc tracking
Reference ID : 47505053 (GPPS)
Stratum : 1
Ref time (UTC) : Fri Nov 05 19:26:59 2021
System time : 0.000001197 seconds slow of NTP time
Last offset : -0.000000044 seconds
RMS offset : 0.000001942 seconds
Frequency : 8.615 ppm slow
Residual freq : -0.000 ppm
Skew : 0.052 ppm
Root delay : 0.000000001 seconds
Root dispersion : 0.000030960 seconds
Update interval : 16.0 seconds
Leap status : Normal
(11/05 12:27:10 richw@equality ~ 2119) $
(11/05 12:27:39 richw@memoryalpha ~ 2000) $ chronyc tracking
Reference ID : 47505053 (GPPS)
Stratum : 1
Ref time (UTC) : Fri Nov 05 19:27:25 2021
System time : 0.000005428 seconds slow of NTP time
Last offset : -0.000024016 seconds
RMS offset : 0.000031762 seconds
Frequency : 30.816 ppm slow
Residual freq : -0.025 ppm
Skew : 1.607 ppm
Root delay : 0.000000001 seconds
Root dispersion : 0.000054530 seconds
Update interval : 16.0 seconds
Leap status : Normal
(11/05 12:27:43 richw@memoryalpha ~ 2001) $
*Rich Wales*
ri...@richw.org
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