Re: Help needed with USB GPS device

[Gary E. Miller]

Yo Gavin!

On Sat, 2 Mar 2024 22:11:22 +0000
Gavin Davenport <gavdav@gavdav.net> wrote:

> Bug raised with Redhat for the 2 issues

Thanks.  Fingers crossed, but no bets.

> I don't have a spot for an external antennae right now but I plan to
> have in the future. Right now it's sat on a windowsill.

That's fine, but older receivers don't work so well that way.

> I might be able to expose a further serial port, I'm honestly
> surprised that's still an alternative compared to USB.

PCIe x4, and M.2, are also options.  USB has too much jitter for many things.

> My ISP is 15msec away at the moment and I'd like to have something
> providing >1msec accuracy if possible. 

Then USB would be less than marginal.

> I'm trying to follow this guide -
> https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html

Good.  There are many.

> I'm now using this approach in chrony
> refclock SHM 0 refid GPS precision 1e-1 offset 0.9999 delay 0.2

That picks up the time from SHM, so no files, or other config, needed.

> refclock SHM 1 refid PPS precision 1e-7

Uh, remember, you have no PPS, so SHM(1) is useless.

> And chrony can see the GPS source as follows:

Yeah, and rejecting the GPS as too jumpy, and the PPS as jsut broken.

> #x GPS                0   4   377    18   -964ms[ -964ms] +/-  200ms
> #? PPS                0   4     0- > +0ns[   +0ns] +/-    0ns

> Can I do anything about this is or is this just the logical
> conclusion with this device ?

That is what it is.  As good as you'll get that.

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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