[Om2008.9] hints and results about using GPS on/with FR

[Matthias Apitz]

Hello,

In the last days (nights :-)) I did some tests with GPS on my FR and
here are the results in compact form; 

HIH

	matthias


...

12. GPS

   Install the following packages:

   # opkg install gpsd
   # opkg install http://www.tangogps.org/downloads/tangogps_0.9.3-r1_armv4t.ipk
   # opkg install openmoko-agpsui
   # opkg install gpsdcontrol_0.3_all.opk

   The last one (gpsdcontrol) removes the starting of the 'gpsd' from the boot
   run-level, which is a good idea at all for saving power;

   One must edit the /etc/default/gpsd to point it to the correct serial device
   of the GSM antenna:

   # vi /etc/default/gpsd
   GPS_DEV="/dev/ttySAC1"

   gpsdcontrol as well powers on the GSM antenna by writing '1' to the drivers
   file; you could do this as well (and you should if you don't use gpsdcontrol)
   in the gpsd start script /etc/init.d/gpsd in the start/stop sequence, writing
   '1' on start and '0' on stop;

   echo 1 > /sys/class/i2c-adapter/i2c-0/0-0073/neo1973-pm-gps.0/pwron

   in any case you must correct a bug in the /etc/init.d/gpsd which tries to kill
   the gpsd, but kills to the running script itself;
   change:

       killall gpsd
   by:

       pgrep -x gpsd | grep -v "$$" | xargs -r kill

   
   The installed tool openmoko-agpsui allows you to check if your GSM antenna
   and chip work fine; some notes about this, GSM and TTFF:

   - openmoko-agpsui does not need the 'gpsd' to be started and it goes out of the
     way if some application (like tangoGPS) instructs the 'gpsd' to read the GSM chip;

   - the internal radio antenna of the GSM chip is in the upper part of the
     Freerunner, above the loudspeaker; while waiting for TTFF (Time To First
     Fix) use the FR in upright position (and with nothing above it, no building,
     no trees, no hand or other parts of your body);

   - I managed TTFF between 23 seconds and 400 seconds which is good enough if you
     keep in mind the small antenna; the Wiki explains about TTFF for cold start
     (and the FR do this) about ~15 minutes:
     http://en.wikipedia.org/wiki/Time_to_first_fix

   - in the 'SS' menu of the openmoko-agpsui you can check after TTFF very good
     the number of the satellites and the strength of their signals; any value
     greater then -145 dbm should be fine; I normally manage average values around
     -130 dbm;
     
   - I normally use openmoko-agpsui to get the First Fix and after this I start
     the gpsd and tangoGPS which find the GSM chip already well located on earth;

   - some screenshoots of openmoko-agpsui can be seen here:  
     http://www.unixarea.de/GPS-test01.jpg
     http://www.unixarea.de/GPS-test02.jpg
     http://www.unixarea.de/GPS-test03.jpg
     http://www.unixarea.de/GPS-test04.jpg


   Some notes about tangoGPS:

   - my cached maps are now stored in the SD card:

     # mkdir /media/card/osm
     # rm -rf OSM
     # ln -s /media/card/osm OSM

   - I pre-fetched maps with some tool from http://www.millions.ca/~stacy/osmtiles.tgz
     which let me define the two points of a rectangle, generate the URL's of
     OpenStreetMap and fetch down the *.png files which I store below /media/card/osm
     where tangoGPS will pick them up; see the README of the tar-ball for more
     details; for example the complete city of Munich inside the Highway-Ring A99
     are some 3000 files for zoom level 11-16 and occupy only ~32 MByte;

   - I run tangoGPS as well in my FreeBSD laptops and connect it to the 'gpsd'
     which runs on the Freerunner, i.e. using the Freerunner as the GSM device
     for my laptop; this give you better view to the maps with tangoGPS, of course :-) 


   more information:

   Wiki: http://wiki.openmoko.org/wiki/Neo_FreeRunner_GPS

...

-- 
Matthias Apitz
Manager Technical Support - OCLC GmbH
Gruenwalder Weg 28g - 82041 Oberhaching - Germany
t +49-89-61308 351 - f +49-89-61308 399 - m +49-170-4527211
e <matthias.apitz at oclc.org> - w http://www.oclc.org/ http://www.UnixArea.de/
b http://gurucubano.blogspot.com/
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