Re: Using non-PPS receiver for ntpd? (Stein, Josh)

[Steve Bourland]

Yo Josh!

On Wed, 9 Jun 2021, gpsd-users-request@nongnu.org wrote:

> Today's Topics:
>
>   5. Using non-PPS receiver for ntpd? (Stein, Josh)
> ------------------------------
>
> Message: 5
> Date: Wed, 9 Jun 2021 14:00:27 +0000
> From: "Stein, Josh" <josh@anl.gov>
> Subject: Using non-PPS receiver for ntpd?
>
>
> Hello everyone,
>
>  I currently only have access to a USB GPS receiver connected to an rPi 
> which does not supply PPS data. Despite the lack of PPS accuracy, I 
> would like to use this receiver as a clock source to the ntp daemon 
> running on that Pi. This Pi in turn will serve time to the other devices 
> on my setup giving me a relative synchronization of their clocks. In 
> this particular instance, I can tolerate some pretty egregious jitter - 
> on the order of tens of seconds.

In my experience, the USB time on some ancient receivers could keep time 
within a second of "real" time.

> My first question is fundamental - given the discussion in the guide 
> here (https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html), is it 
> even feasible to use a non PPS receiver in this role?

My gut response is yes, but if Gary or David (Taylor) come along and 
advise against it, they know MUCH better than I do.
I fully expect Gary to ask why you don't spend the <$30 to get a GPS with 
PPS, a question I would also pose.  Is this a question of you can't bring 
a new GPS into the environment?
I assume you're in the same situation I am, a network that has no Internet 
connection.  Given that, and that the Pi will only have this one source, I 
believe chrony may handle that situation better, but again, my memory on 
this is rusty.
                                        Best of luck!
                                           Steve