Re: Using non-PPS receiver for ntpd?

[Greg Troxel]

"Stein, Josh" <josh@anl.gov> writes:

>   So in this instance (not using PPS), do I just ignore any mention of
>   configuration when moving forward with the guide? Also just leaving
>   out the PPS section of the ntp.conf?

probably.  Most of my experience either predates the HOWTO or I wasn't
looking at it.

> e.g. do not enter the lines :
>
>    # GPS PPS reference (NTP1)
>    server 127.127.28.1 prefer
>    fudge 127.127.28.1 refid PPS

You can enter them or not.  That just tells ntpd to expect a PPS source
in gpsd shm location 1, and gpsd won't be writing it.

So really it's just

  running gpsd

  putting the 127.127.28.0 line in ntp.conf, and I'd use 100 ms
  as the fudge until you have a better estimate.

Looking at the HOWTO briefly, it is highly focused on PPS and high
accuracy.  I don't know of any documents that try to explain the path to
sub-100ms accuracy with serial only.  That's partly because it's
just not that hard, and partly because some here don't want to do that.

Note that there are lots of issues with configuring ntpd, such as using
network servers and whether ntpd should be able to follow just the local
reference with no others (tos minsane, etc.).   These really aren't
about gpsd.

Long ago, I set up a system running gpsd with a u-blox 4 and ntp, and
had about 100 computers synced to it.  We had no even semi-reliable
internet, and all the computers being within 10s of ms of each other and
50 ms of real time was considered a great outcome, suitable for data
collection for what we were really trying to do.

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