Re: Help needed with USB GPS device

[Gary E. Miller]

Yo Gavin!

On Sat, 2 Mar 2024 11:18:13 +0000
Gavin Davenport <gavdav@gavdav.net> wrote:

> >>Replies to the list please.  Private email is for paying clients.  
> Apologies, hadn't spotted that was happening.

No big.  A common mistake.  Better for the whole list to help with your
issues.

> >>gpsdebuginfo is part of gpsd, so you already had it. But
> >>the linked one is the latest one.  
> gpsdebuginfo is not in the fedora gpsd (rpm) package I have.

Can you please file a bug report with them then?  As you can see,
gpsdebuginfo makes debugging very much easier.

> >>>>># Magic Hat enabled.  
> >>Are you on a Raspberry PI?  If not, this should be off.  
> No, a mini-itx PC and fedora 38. I guess Redhat are building with
> that enabled.

Can you please file a bug report with them then?

> The devices it tries to use are in /etc/sysconfig/gpsd. I have
> removed /dev/pps0 and we now have:
>   00:00:02 /usr/sbin/gpsd -n /dev/ttyUSB0

Looks god.

> >>And there is the answer to your GPS type.  It is s SiRF-III.  A tad
> >>old, not so good indoors.  My condolences.  SiRF was bought out, and
> >>disappearing from the market.  
> The label on the device itself says it's a BU-353 (It is 10+ years
> old and it was supplying GPS positions to a car PC for years)

Yes, The BU-353 uses a SiRF-III chip.  So it all cross-checks.

> Slightly different discussion then - what's an affordable alternative

Since COVID, the price and availablility of GNSS receivers is all over
the place.  Picking the right one for you depends on how you will use it
(indoors, outdoors, fixed, mobile, etc.), what you need from it (3m, 1m,
1cm accuracy, 1ms, 1us or 1ns accuracy). and what you will connect to
(PCIe, real RS-232, fake RS-232, Raspberry Pi, etc.).

So first you need to choose your niche.

> ? Should I be avoiding all USB GPS devices ?

Depends on the answers to the above questions.  If 1ms time accuracy is
good enough, then that are some good devices available.

> 
> >>> NTP0 1709284857.228735488 1709284856.591468173
> >>> 1709284856.570000000 0  -1  
> >>Not good enough to be a good NTP server.  
> I read the ntpshmon man page but I couldn't work out whether the
> source was good enough to be an NTP source.

There is no one, true, "good enough".  It all depends on your accuracy
needs.  For an NTP pool server, your ISP latency might be 10ms, so a
receiver that good is sufficient.  For a cal lab, you might want well
under 1 us.

Best to ask the chronyd people.

> >>> + cat /etc/sysconfig/gpsd
> >>> # Options for gpsd, including serial devices
> >>> OPTIONS=""
> >>> # Set to 'true' to add USB devices automatically via udev
> >>> USBAUTO="false"
> >>> DEVICES="/dev/ttyUSB0 /dev/pps0"  
> >>                        ^^^^^^^^^^  Wrong, remove it.  
> I don't quite follow this. I remove /dev/ttyUSB0 ?

If you are using a fixed width email font, then the carets are under the
"/dev/pps0".  You got that part right abive.


> >>> I didn't know USB GPS devices tended not to have PPS.  
> >>And now you do.  
> What's the alternative ? searching the web for GPS devices gives me
> lots of handhelds, lots of USB ones but I don't know how to find
> which ones offer/support PPS. Maybe this ?
> https://gpsd.io/hardware.html

Sadly that list is a bit out of date, and post COVID, a moving target.
Let us know your requirements, then we can make timely suggestions.

> >> If no PPS is good, then you just need to figure out if gpsd is
> >> talking to
> >>chronyd.  Another email from another list user had things to check
> >>on that part.  
> I'm confused by this. Conceptually I think chrony is querying gpsd
> data.

Nope.  chronyd does not query gpsd.  gpsd writes to special files
that chronyd waits for.  

> Do I need to inform gpsd about chronyd somehow ?

No, you need to inform chronyd about gpsd somehow.

This is explained in the GPSD Time Service Howto that I already provided
you the link to.


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

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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