Re: [gpsd-users] Get fix mode with disconnect antenna

[Yakov Shmulevich]

Hi Gary,

On Tue, Nov 19, 2013 at 8:11 PM, Gary E. Miller <address@hidden> wrote:

Yo Yakov!

On Tue, 19 Nov 2013 09:58:42 +0200

Yakov Shmulevich <address@hidden> wrote:

> > > You don't understand me, I disconnect the antenna, so at this time
> > > the PVT data by sure changed.
> >
> > Are you sure?  Do you see that in the debug output?  Most GPS will
> > just stop sending anything when they lose the antenna.
> >
> I run gpspipe at this  time and see all periodical NMEA messages come.
> And in the GGA message I see GPS Quality Indicator=0 (Fix not
> available or invalid)

Can you make a copy of the gpspipe output and annotate it with the
remove event?

Follow gpspipe output with antenna connected: 

$GPGGA,061139.00,3206.6722,N,03450.3224,E,1,09,1.1,-0019.1,M,0018.4,M,,*73

                                                                                        | 

                                                                                        -- GPS Quality Indicator(1=GPS SPS Mode, fix valid)  

$GPGSA,A,3,12,25,18,21,29,73,79,82,83,,,,1.8,1.1,1.4*30

                      |

                      -- Mode(3=3D)

$GPGSV,5,1,17,02,05,047,,05,28,063,,12,30,135,25,18,12,182,31*76

$GPGSV,5,2,17,21,52,236,30,25,71,138,27,29,58,017,38,31,32,278,33*73

$GPGSV,5,3,17,65,03,024,26,66,27,068,,67,24,127,,73,15,329,38*70

$GPGSV,5,4,17,79,36,202,29,80,50,281,,81,30,042,,82,48,336,45*75

$GPGSV,5,5,17,83,10,273,30*40

$GPRMC,061139.00,A,3206.6722,N,03450.3224,E,000.00000,074.7,201113,,,A*55

                                       |                                                                                                    |

                                       -- Status(A=Data Valid)                                                            -- Mode Indicator(A=Autonomous mode)

Follow gpspipe outout with antenna disconnected: 

$GPGGA,061324.00,3206.6721,N,03450.3225,E,0,00,9.9,-0018.9,M,0018.4,M,,*7E

                                                                                        | 

                                                                                        -- GPS Quality Indicator(0=Fix not available or invalid)  

$GPGSA,A,1,,,,,,,,,,,,,9.9,9.9,9.9*30

                      |

                      -- Mode(1=Fix not available)

$GPGSV,5,1,17,02,05,047,,05,28,062,,12,30,136,,18,13,181,*73

$GPGSV,5,2,17,21,53,236,,25,70,139,,29,58,018,,31,32,277,*7F

$GPGSV,5,3,17,65,02,023,,66,27,067,,67,25,127,,73,16,328,*75

$GPGSV,5,4,17,79,35,202,,80,50,280,,81,29,043,,82,48,337,*75

$GPGSV,5,5,17,83,11,274,*45

$GPRMC,061324.00,V,3206.6721,N,03450.3225,E,000.00000,074.7,201113,,,N*41

                                       |                                                                                                    |

                                       -- Status(V=Navigation receiver warning)                             -- Mode Indicator(N=Data not valid)

 

> More then, if I reconnect my client by gps_close() and gps_open() I
> got gpsdata.fix.mode = MODE_NOT_SEEN.

Good.

> But if I not reconnect my client I continue to get MODE_3D

Expected, that means you client has cached the last state.

Why it is expected? 

If so, I am not understand how the libgps works in case of  shared memory export.

As it is write in your documentation: "Whenever the daemon recognizes a packet from any attached device, it writes the accumulated state from that device to a shared memory segment."  So, I expect that every time than I call gps_read(), it brings me the last updated data from shared memory. What means "client has cached the last state"?

I would to return to my question again: Why then I re-open my session by gps_close() and gps_open() I start to get the right PVT data?

> > > But I got the data as before disconnecting antenna, include
> > > gpsdata.fix.mod=MODE_3D.
> >
> > Is so, we need to see some debug output to see what is happening.
> >
> What debug print you need? I can run the gpsd with -D 7 and send you ?

gpspipe will do to start.

> > > I found the workaround, but it seems me very ugly.
> > > Now every time that I want to get PVT data, I open the session by
> > > gps_open(), and after I get the PVT data I close the session by
> > > gps_close(). Also this solution have some strange behavior - I
> > > found that after gps_open() I get right PVT data only after 3-5
> > > gps_read().
> >
> > Sounds like you are not starting gpsd with -n.  Can you confirm how
> > you are starting gpsd?
> >
> gpsd -b -n /dev/ttyUSB1

That is good, except we discourage the use of -b.  That is intended mostly
for broken bluetooth GPS.  Why are you using that?

I am working with GPS module through FT2232H with 1PPS on DCD pin. So, the GSP receiver is connected via USB.

For -b is was mentioned also about USB, therefore I add this options.

Is it wrong or can be used?

Not knowing what you are doing in the gps_read() it is hard for us to
comment.  Can you see this behavior in cpgs or gpspipe?  Something we
can duplicate?

For cgps:  then I disconnect the antenna the window with satellites information is cleared, 

but in window with PVT data remained the same information as before antenna disconnecting.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588