[gpsd-users] ntpd time accuracy with gpsd and 1PPS

[Yakov Shmulevich]

I am setup startum-1 NTP server on my device based on GPS receiver with 1PPS signal connected. For this, I am using ntpd and gpsd interconnection.

So, I add the follow lines in /etc/ntp.conf:

     server 127.127.28.0 minpoll 4 maxpoll 4

     fudge 127.127.28.0 time1 0.535 refid GPS

     server 127.127.28.1 minpoll 4 maxpoll 4 prefer

     fudge 127.127.28.1 refid PPS

and restart gpsd and ntpd.

After some time I got ntpd synchronized with 1PPS time source:

address@hidden ~]# ntpq -p

     remote           refid      st t when poll reach   delay   offset  jitter

==============================================================================

+SHM(0)          .GPS.            0 l    2   16  377    0.000   78.510   4.351

*SHM(1)          .PPS.            0 l   11   16  377    0.000   -0.017   0.057

xmivzakim.net    64.236.96.53     2 u   28   64  377   18.184   -9.893   2.426

 LOCAL(0)        .LOCL.          10 l   63   64  377    0.000    0.000   0.001

Already is good, but I have some questions:

1. Did the offset (17 microseconds) give the system time accuracy relatively to the time provided by GPS receiver? Or we have some additional delay related to the time that take gpsd for interpreting 1PPS signal? If yes, what is this time delay value?
2. Did you know any tools that give possibility to measure system time accuracy relatively to the time provided by GPS receiver?

Thanks,

Yakov