Re: NTP via tcp NMEA feed

[Gary E. Miller]

Yo Nick!

On Fri, 14 Oct 2022 13:16:54 +0100
Nick Taylor <nicktaylor@dataskill.uk> wrote:

> You may have seen that we are working with using tcp NMEA feeds for a 
> device that we built - basically certain customers have existing GPS 
> devices and wish to use feed from that instead of separate antenna...

Why?

> Additionally often Internet connectivity is firewalled back so we
> drop back to using GPS time rather than proper NTP

VPNs solve that easily.

> Now I notice that I don't seem to see NTP coming through from NTP
> feed 

Uh, what is an NTP feed?  I assume you mean NMEA feed.

>- the only success we had was using the shm feed and with normal
> setup ntpshmmon shows normal time feed coming through nicely which we
> can then link into chrony.

There is no NTP in NMEA.  The best you can ge is to take the time from the
NMEA, and that will have a lot of jitter.

> Is this expected behaviour or a bug?

I'm not sure what you are expecting, but what you see is normal.

> Is there any way to still get
> NTP from a tcp NMEA feed??

Nope.  Totally different protocols.  NTP on the net has a handshake,
NMEA does not. NTP in hardware, is a dedicated wire, NMEA in hardware
is serial bits.  NTP can get you (almost) to 1 ns, NMEA is lucky to get
you to 1 second.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

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    "If you can't measure it, you can't improve it." - Lord Kelvin

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