Howto Test Your GPS with agpsui
How to test AGPS on the Neo Freerunner
Apparently there are some questions regarding the GPS on some freerunners. There has been anecdotal evidence of time to first fix (TTFix) from between 40 seconds up to 30 minutes. Some owners have reported that they can't achieve TTFix and there are some Freerunners that appear to have bad solder joints between the GPS antenna connector and the Freerunner main PCB. There is a need for a proper method of testing and a howto describing how to test if a Freerunner has a abnormal TTFix or not.
This guide will assume that people has either managed to
- a. correctly configured usb-networking or
- b. correctly configured wifi-networking or
- c. is capable of downloading opkg packages from
buildhost.openmoko.org/daily-feed/ to a computer and then transfer them to the Freerunner with scp.
First of all, what were trying to do is to get a estimate on how well the GPS works. This means that any numbers you aquire is _not_ necessarily comparable with somebody else's. If Alice reports seeing 13 satelites with an signal strength of ~ -140 dBm and got a FFix in 4 minutes then Bob can't assume he has a broken GPS if he saw only 5 satelites at a signal strength of ~ -145 dBm and it tok 45 minutes to get a FFix. If Charlie on the other hand saw only 2 satelites @ ~ -157 dBm and didn't get a FFix after leaving the freerunner on a table for two hours in the midle of nowhere and the freerunner had a clear 360 degrees view then Charlie can safely assume he indeed has a broken GPS.
In fact, these are the number we want you to report: Serial number on your phone. This number is printed on both the black box packaging and under the battery of your freerunner. All serialnumbers are 9 digits and they begin with S/N: 8A86<xxxxx> In adition, we would like you to report then number of satelites your phone managed to detect and a estimate on what 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.)
- Assuming you have a fresh-from-the-factory freerunner, first get some
basic networking configured. this is beyond the scope of this howto.
- ssh to the freerunner :
- 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.)
- 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 email@example.com:/home/root/.
- Install the package openmoko-agpsui:
opkg install openmoko-agpsui
opkg install openmoko-agpsui_*.ipk
- 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 Charlie's midle 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?
- Find a place where your freerunner can sit on a stable surface or
at least 30 minutes without being molested, fondled or even touched. 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. ;) )
- 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
- Now press "Power on" and then "SS", then leave the darn freerunner on
the safe and flat surface for _at least 30 minutes without moving or touching it_. 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 between millimeters and centimeters, now imagine godzilla (you) smashing them. )
- 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.
- 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!
- Now report any anomalities to the mailinglist 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