Re[2]: NTP with only GPS/PPS flags PPS as falseticker

[Nick Burkitt]

Hi Greg.

Set fudge on the non-PPS GPS time (which is based on mesage arrival).

It is typically off a bit, and I dimly remember 100 ms late (on one

computer, running a different OS, with a different receiver -- just

I've fiddled with the value of the time1 option on the shared memory driver refclock line (refclock shm unit 0 refid GPS minpoll 3 maxpoll 4 time1 0.080 flag4 1), and it seems to make a slight difference. Occasionally I see a '+' next to SHM(0) in nptmon when disconnected from the network, but only briefly. Although the PPS offset no longer seems to drift...

     remote           refid      st t when poll reach   delay   offset   jitter
xSHM(2)          .PPS.            0 l    6    8  377      0ns -21.29us  3.316us
 0.us.pool.ntp.o .DNS.           16 u    -    8    0      0ns      0ns  1.907us
 1.us.pool.ntp.o .DNS.           16 u    -    8    0      0ns      0ns  1.907us
 2.us.pool.ntp.o .DNS.           16 u    -    8    0      0ns      0ns  1.907us
 3.us.pool.ntp.o .DNS.           16 u    -    8    0      0ns      0ns  1.907us
xSHM(0)          .GPS.            0 l    1    8  377      0ns 6.4961ms 3.8104ms
 pool.ntp.org    .POOL.          16 p    -    8    0      0ns      0ns  1.907us
ntpd ntpsec-1.1.8+ 2020-03-04T20:55:58Z        Updated: 2020-03-19T01:08:13 (4)
 lstint avgint rstr r m v  count rport remote address
      0  0.397    0 . 6 2    441 41040 localhost

 

Read about minsane. If you want to sync to just GPS, then you need to

accept a single source. ntpd by default does not do this.

The documentation (https://docs.ntpsec.org/latest/miscopt.html) claims that the default value for minsane is 1

Turn on ntpd debugging and figure out why it's doing what it's doing.

I've tried setting debug to 10 (i.e. /usr/local/sbin/ntpd -D 10 -g -N -u ntp:ntp), but nothing interesting appears in ntpd.log.

I'll try my luck on the ntpsec mailing list.

Thanks,

-Nick