Howto Test Your GPS with agpsui
How to test AGPS on the Neo Freerunner
Some Freerunner GPSs appear to be insensitive, taking a long time, or not obtaining a fix at all, even in ideal condtions.
Time to first fix (TTFix) should be well under 15 minutes in all cases when the Freerunner has a view of the sky, however some appear to have bad solder joints between the GPS antenna connector and the Freerunner main PCB.
Why do I need to test?
This guide outlines how to gather data to help fix this problem. It's important for both those with working GPS, and those with not-working GPS to perform this test.
There may be some with marginal GPSs that appear to work, but are drastically less sensitive than the norm.
This guide assumes that you've managed to configure your Freerunner so that you can install opkg packages from buildhost.openmoko.org/daily-feed/ , either directly through wifi or usb networking, or by downloading them to a desktop and transferring them with scp.
We need to find the average reported signal strength of phones in a similar condition.
This should be outside, with no obstructions too near the horizon. A location with nothing within 30 degrees of the horizon is adequate. The occasional sticking up building or tree is not a big issue.
The phone should be placed upright, with the screen upright in order to make the antenna (at the top of the phone) most sensitive - if placed flat on a table, it will have very poor sensitivity to half the satellites in the sky.
Could you report the following numbers.
- Serial number, this number is printed on both the black box packaging and under the battery of your freerunner. It's 9 digits and begins 8A86<xxxxx>
- Number of satelites your phone managed to detect and a estimate of the average signal strength in dBm for those satelites. (We don't need to know the average for each satelite, just the average for all satelites.)
- How long time it took to get First Fix.
- 1. Assuming you have a fresh-from-the-factory freerunner, first get some
basic networking configured. this is beyond the scope of this howto.
- 2. ssh to the freerunner :
- 3a. If you have a working wifi or usb network:
( Ignore all warnings about missing signature files, the openmoko repository haven't got any at the moment.)
- 3b. Or if your doing this the basic way, download openmoko-agpsui and
then transfer to your freerunner:
wget http://buildhost.openmoko.org/daily-feed/armv4t/openmoko-agpsui_*.ipk scp openmoko-agpsui_*.ipk firstname.lastname@example.org:/home/root/.
- 4. Install the package openmoko-agpsui:
opkg install openmoko-agpsui
opkg install openmoko-agpsui_*.ipk
- 5. After having completed all these steps sucessfully your ready to
test your freerunner. Charge your battery to full capacity (can't hurt), wait for a clear weather and then check out places you can visit. The ideal place is in the middle of nowhere, but the next best thing is a area with clear view of the sky and no towering foliage or buildings nearby. Nice weather is a must have because you don't want your shiny freerunner to get soaked do you?
- 6. Find a place where your freerunner can sit on a stable surface for at least 30 minutes without being molested, fondled or even touched.
Ideally the FR it should sit inside a (empty) ceramic cup pointing upwards for maximum coverage. Second best is to leave the freerunner with the screen facing upwards, preferably with the top of the freerunner facing northish. (Not a requirement, just trying to be scientific. ;) )
- 7. on the freerunner Graphical User Interface you should find a program
called "Openmoko AGPS UI". Run this program. The program has several interesting features. on the top left side of it's UI you can find the tabs: "Run" "SS" "AZ" "plot" "Log"
- "Run" is the current picture, here you start and stop the GPS
- testing software. Everything with the word "Reset" reset's the
- sampling and/or the chipset. "Power on"/"Power off" powers up
- (or down) the GPS chipset and starts logging. "One Fix" starts
- the logging but powers automatically down after having managed
- to get FFix from a single satelite.
- "SS" gives you signalstrength, calculates average
- signalstrength, identifies the differnt satelites by number and
- of course lets you count the number of satelites _IF_ it can
- manage to find at least 1 satelite.
- "AZ" gives you the position of the different satelites _after_ it
- get's a FFIX. Otherwise a satelite is "defaulted" to being
- somewhere over the northpole. (on a _very_ thight polar orbital
- indeed. ;) )
- "Plot" gives a estimate on where the different satelites say _you_ are,
- usually with a margin of +-5 meters. (10 meters in difference.)
- "Log" gives you the NEMA output from the GPS chipset. Interesting for
- those who can read NEMAish, not so interesting for the rest of
- 8. Now press "Power on" and then "SS", then leave the Freerunner in a vertical position for _at least 30 minutes without moving or
touching it_. (a large mug works well as a stand) Do not stand over it either, your blocking those precious satelite signals! ( GPS runs at ~ 1,2-1,5 Ghz, this is a weak signal with a wavelength of 20cm, now imagine godzilla (you) smashing them. )
- 9. After having spent twidling your thumbs or reading a good book for
30 minutes you get to press the "dBm" button to translate those nasty dB.Hz into goodness dBm signals. If you've gotten FFix some of the blue blue bars has a nice black thing on the bottom. And on top of screen above each bar there are two numbers, the top denoting the maximum signal you got from each satelite and the lower number the average signalstrength.
- 10. If you haven't managed to get a FFIX your either doing something
wrong or your one of those unlucky guys (gals) with a bad solder or something else that probably requires shipping the phone back to your supplier/openmoko. If you got only 3-4 satelites and had a lousy reception (say -150 to -160 dBm) you /might/ have a faulty freerunner but you should try again somewhere else at another time of the day just to make sure. If you had a lousy reception but did get a FFix, try again somewhere else to se if you can improve your record. If you on the other hand found several satelites( +5) and had quite a good reception (maybe > -145 dBm ? ) the you probably has a working phone. Now, I'm not a radio or wireless engineer, so any numbers in dBm should be taken with a grain of salt. But the main thing is that you followed the basic instruction and did a thorough scientific test! You did Science!
- 11. Now report any anomalities to the apropriate mailinglists or the guys that told
you to read this howto.
http://wiki.openmoko.org/wiki/Getting_Started_with_your_Neo_FreeRunner http://wiki.openmoko.org/wiki/FreeRunner_GPS_antenna_repair_SOP http://wiki.openmoko.org/wiki/USB_Networking http://en.wikipedia.org/wiki/Global_Positioning_System