Neo FreeRunner GPS
GTA02 GPS Hardware
GTA02 using the u-blox 4 hardware and could use u-blox 4 Assist Online GPS A-GPS servces. GTA02 hardware design not comply with official Assist Offline service requirement.
Assist Online/Offline comparsion
th "A"GPS support could cut TTFF time from 40 secs to 10-20 seconds. And the valid time of assist now download is about 4 hours. You could also check the following address:
Due to the u-blox 4 need to have extra flash to storage up to 14 days of offline data (90 KBytes).
Each download package could have up to 4 hours vaild data to assist TTFF. For u-blox Assist Online, you have to provide approximate longitude/latitude and time to get the corresponds "almanac" and "ephemeris" package. This might be base on application design for how to provide the longitude/latitude. User could select the location area from list menu or world map, or better implementation using the GSM/wi-fi location technique/service.
u-blox Assist Online implementation
For GTA02 default shipment image, there is no A-GPS/GPS supported software inside. You could find the u-blox A-GPS online implementation document here:
- Documentation: http://people.openmoko.org/matt_hsu/ImplementationAssistNowServerAndClient(GPS.G4-SW-05017-C).pdf
And implementation code in following address.
Here is a brief script to run this application:
#!/bin/sh echo 1 >/sys/bus/platform/drivers/neo1973-pm-gps/neo1973-pm-gps.0/pwron ./agps-onlinec -c full -u youraccount -k yourpasswd -la 25.073270 -lo 121.574805 -p 999999.00 cat /dev/ttySAC1
-la 25.073270 -lo 121.574805 is reference latitude/longtitude
u-blox Assist Now account application
And account application is send a mail to email@example.com
without content and title. And not all mail account are accepted/could get reply. since the protocol is pretty straight forward, implement an extra proxy to scale up user should be easy.
u-blox Assist Offline service could provide up to 14 days of valid assist GPS data in single download package. But Assist Offline service need an extra flash to storage Almanac data, and u-blox 4 will automatically use these data while system start up. GTA02 don't support Assist Offline.
u-blox Assist Offline implementation
Due to the u-blox 4 need to have extra flash to storage up to 14 days of offline data (90 KBytes), GTA02 don't have it. I would very interested if there is another way to twist it around, but not likely, so far. Offline sample data you could find in the following addesss:
And u-blox did provided source code of Assist offline server implementation and ubx header, you could find it here:
Possible implementation mechanism
We can use the same protocol as the online assist to provide the time, last location, almanac and ephemeris data that would be held in the extra flash storage when we power up the GPS. Time is available from the local clock, and we can save location, almanac and ephemeris when the GPS is shut down. We may be able to have a better guess at startup location based on GSM cell ID, WiFi access points, or by the user selecting an area on a map.
Some Ruby tools already exist for downloading and uploading Almanac and Ephemeris. See http://docs.openmoko.org/trac/browser/developers/alphaone/u-blox
Protocol specification (html-help format): http://www.u-blox.com/customersupport/gps.g3/ANTARIS_Protocol_Specification(GPS.G3-X-03002).chm
Sample header could be found here: ubx.h
Conversion between lat/ln and ECEF xyz coordinates: http://www.u-blox.com/customersupport/docs/GPS.G1-X-00006.pdf
GPS test program
Openmoko projects has a GPS test program called AGPS UI in following address:
Pre-compilied ipkg file, could download from here AGPSUI test program
Install package using:
- root-omgta02# opkg install openmoko-agpsui_0.1+svnr7-r0_armv4t.ipk
This is actually in the repositories now, simply do:
- opkg install openmoko-agpsui