Re: GPS time sync with chrony and ESE serial device

[Devren Yener]

Gary, I agree with your economic point, especially knowing how much time I’ve already spent trying to figure this out. Could you recommend a good accurate $100 GPS unit which is compatible with gpsd/chrony? A lot of the ones on the official gpsd hardware list do not have PPS. And a new unit by the same company as my old one (ESE) is over $1400 (including built-in NTP server!).

Greg, to respond to your suggestion about using PPS without gpsd — my challenge is figuring out how to get Linux to know that there is a PPS signal on my serial port. When I boot up my system, I have a /dev/ttyS0 but not a /dev/pps0. I have found three tools that can create a /dev/pps0, namely, (1) gpsd, (2) ldattach (pre-installed in my Ubuntu), and (3) ppsldisc (from the pps-tools package). I actually made the most progress with the last of these three; I am able to sync time gloriously with chrony for about five minutes, before the PPS device mysteriously stops working. Also, out of all these programs, only gpsd installs itself as a systemd service, which is what I really want, so that it starts consistently on boot.

I only asked about gpsd out of respect for this forum, but if anyone has advice about getting the PPS to work without gpsd, I would gladly accept it!

Thank you again,
Devren

On Wed, Mar 4, 2020 at 1:41 PM Gary E. Miller <address@hidden> wrote:

Yo Devren!

On Wed, 4 Mar 2020 13:08:26 -0500
Devren Yener <address@hidden> wrote:

> Thanks very much Gary for your help and advice!  We were afraid we
> might have to buy new equipment, but I figured it's a simple enough
> signal, I'd be very surprised if there isn't some way to get it
> working in Linux.

With Linux there is always a way.

> (It works in Windows and DOS after all, with the
> manufacturer's ancient software... but I don't want to use these for
> a time server!)

You'd be surprised how well old machines can do NTP.

> Do you still think gpsd will not be able to work with the signal?

It could work.  But someone would need to write a new driver for this
terse protocol.  A lot of work just to avoid spending $100 for a
replacement.

If someone had the budget, and a serious need, I'd skip using gpsd.
A simple python program could read the simple serial data, check the
lock signal, then pass on the time to SHM().  The chronyd and/or ntpd
can read the shim with a simple configuration file change.

A good programmer familiar with the various parts could do it in a
day.  A fair programmer unfamilar with the parts, but with guidance,
might take a week.  All of a sudden $100 looks cheap.

RGDS
GARY
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