[debian & gps] How to check gps

-stacy slm3095om at Millions.Ca
Wed Sep 24 06:55:51 CEST 2008

This thread has stirred up a lot of incorrect information, I will try to
help with the original question and then try to "mudify the
fuzzifications" as it were...

Christian Weßel wrote:
> Hello,
> tangogps and fso-gpsd were installed from <http://ftp2.de.debian.org>,
> but I get no fix.
> In the Trip tab tango shows allways an alternating GPS Time (Tue
> 1999-11-30 00:00:00 or Fri 1999-11-31 01:00:00) and Satelites: 11/0. The
> rest is zero.
> The zhone internal gps appl. shows at the start view at all items N/A,
> and at the satelite view are about 10 satelites shown.

That tells me that your GPS is powered on, something (we will get to
this later) is talking to your GPS and receiving data and that Zhone and
tangogps are both talking to that something. All of that is good... it
means that it is not likely an application problem at this point.

> The FR ran the whole evening next to a window in a wooden house, but it
> got no fix. I couldn't remove the SD card of using Debian installed on
> it :-}. Is my FR one of these ones with the SD card problem? Or is it
> also fixed by Debian distro?

Next to a window in a wooden house is not a guarantee that you will get
a fix indoors. There are only certain areas in my house where I can get
a fix, once the fix is established I can get a position anywhere in my
house (including the basement).

> How can I check my GPS? How can I bring it up running?

I would recommend that you do your testing outdoors in an open area.
Outside with a clear view of the sky you should be able to get a fix in
less than ten minutes. If you can, try using an external GPS antenna, 
that is the easiest way to avoid the SD card interference.

Now I will try to clear up some confusion about FSO/GPS. I completely
understand why people are confused, I had to do a fair amount of digging
to figure this out. I am reasonable certain that this is accurate, but YMMV

First, lets look at the players in this mess...

gpsd - this is our good old friend from http://gpsd.berlios.de/ "True
        gpsd" someone called it.
ogpsd - this is a subsystem of FSO's frameworkd. It replaces gpsd
         it implements the Gypsy API communicating with applications
         via dbus
fso-gpsd - is a compatibility shim to translate Gypsy messages for
            applications that expect gpsd
tangogps - a map/gps application
tangogps-fso - a version of tangogps that has been modified to
                understand Gypsy messages

I don't know how you could find this confusing.

That is why I said "something is talking to your GPS", if you have a
stock FSO then you have ogpsd talking to the gps and tangogps (the FSO
version) and Zhone are getting their data via Gypsy. You don't need gpsd
or fso-gpsd in this situation.

Fox Mulder wrote:
> For me fso-gpsd didn't work right so i changed back to gpsd and
> everything works like a charm with gps. :)
> Maybe you try installing gpsd and deinstall fso-gpsd.

When you say "everything works like a charm" do you mean "everything"?
Does Zhone's location test app work? I would be very surprised if it
does. However, if the only applications you care about work with gpsd,
this is definitely an option.

Dima Kogan wrote:
> To check the raw data coming out of the device, do
> cat /dev/ttySAC1 | grep GGA

That will only work if the GPS is powered on and in NMEA mode. In FSO,
the power state is controlled by ogpsd, if there no client has requested
a GPS resource, then the gps is left off, so your test would return
nothing. Also, ogpsd uses the UBX binary protocol not NMEA, so your test
would still return nothing.

>                 The gpsd daemon (whether true gpsd or fso-gpsd) should
> make this data available on port 2947. Check this with
> nc 2947 | grep GGA
> If the daemon works, you should get the same data here, as above. 

By default, gpsd (true gpsd, as you called it) will not return data to
network connection without you asking for it. I don't know how ogpsd
behaves. If you connect with telnet

telnet localhost gpsd (or if you prefer telnet 2947)
and type p followed by a <return> you will either get

GPSD,P=xxx yyy     where xxx and yyy are your lat and long

Sascha Wessel wrote:
> Exactly this is the most common problem. Please...
> * do NOT echo 1 > neo1973-pm-gps.0/pwron

As I said, ogpsd will take care of turning the GPS on and off, so this 
is good advice.

> * do NOT read from /dev/ttySAC1
> * do NOT write to /dev/ttySAC1

Regardless of whether it is gpsd or ogpsd, this is good advice (for 
normal operations) for debugging purpose you can do it, but it could 
confuse things.

> * do NOT run the original gpsd

This is especially true if you have not disabled ogpsd. Having both of 
them trying to talk to the gps will cause problems (remember, one uses 
NMEA while the other use UBX).

I hope this helps.


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