subject:"GTA02 GPS rework for SD card interference issue"

Re: Warranty after fix for GTA02 GPS rework for SD card interference issue

2008-08-05 Thread -stacy

Andy Green wrote:

 About the 600sec thing, you can get the GPS chip to report 4 times a
 second instead of once a second, maybe that can be to do with it.  But
 it is strange, noticing the heavy filtering on our results I wonder if a
 lot of those samples coming so quickly were actually synthetic.

It would seem that they are synthetic and have to do with how GPSD 
parses and interprets NMEA sentences. The other two reference receivers 
are put in SiRF mode and don't seem to suffer this effect. Has anyone 
figured out how to kick the GPS receiver into UBX mode? I would be 
curious to see if that changes anything.

 For the last result, it seems to show only 2 / 2500 results from GPS are
 within 20 Million meters of the location.  It's hard to square that with
 the other decent results that have been reported for tracking, including
 ones pulling maps from SD Card, although I guess you are spamming the
 card as hard as you can for this test.

It seems that gpsprof gets a value of 10,000,000,000 for NaN and doesn't 
check if lat/long values are in range before calculating the average. It 
doesn't take very many 10 Billion values to really screw up the average 
:-) I modified gpsprof to toss out invalid lat/long values.

 What actually happened when gpsd died?  With that and the extreme nature
 of the last result I wonder if something else goes on.
 
 One last thing, the voltage scaling and clock rate reduction patches
 aren't in the kernel you used, they should be around in tomorrow's
 packages: if you have 600 sec to spare it would be interesting to see if
 they made any change :-)

Additional test results (from 20080802) are up at 
http://www.millions.ca/~stacy/neoFreeRunner/gpstale.html

I did some more testing yesterday after compiling the latest version of 
GPSD for the FreeRunner (it no longer dies when I spam the SDCard... 
that's progress :-) but have not yet got the results pulled together.

-stacy

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Re: Warranty after fix for GTA02 GPS rework for SD card interference issue

2008-08-05 Thread Andy Green

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Hash: SHA1

Somebody in the thread at some point said:

Thanks for your work Stacy.

| About the 600sec thing, you can get the GPS chip to report 4 times a
| second instead of once a second, maybe that can be to do with it.  But
| it is strange, noticing the heavy filtering on our results I wonder if a
| lot of those samples coming so quickly were actually synthetic.
|
| It would seem that they are synthetic and have to do with how GPSD
| parses and interprets NMEA sentences. The other two reference receivers
| are put in SiRF mode and don't seem to suffer this effect. Has anyone
| figured out how to kick the GPS receiver into UBX mode? I would be
| curious to see if that changes anything.

It's actually documented by Ublox in here (Okular eats it)

http://www.u-blox.com/customersupport/gps.g3/ANTARIS_Protocol_Specification(GPS.G3-X-03002).chm

Here's a UBX packet generator in Bash

http://lists.openmoko.org/pipermail/openmoko-kernel/2008-July/003782.html

and here is how to inject the packets from Ash

echo 0  /sys/class/i2c-adapter/i2c-0/0-0073/neo1973-pm-gps.0/pwron 
sleep 1s  echo 1 
/sys/class/i2c-adapter/i2c-0/0-0073/neo1973-pm-gps.0/pwron  stty -F
/dev/ttySAC1 -echo  cat MY-UBX-PACKET /dev/ttySAC1  cat -u
/dev/ttySAC1 | grep -v ^$

| For the last result, it seems to show only 2 / 2500 results from GPS are
| within 20 Million meters of the location.  It's hard to square that with
| the other decent results that have been reported for tracking, including
| ones pulling maps from SD Card, although I guess you are spamming the
| card as hard as you can for this test.
|
| It seems that gpsprof gets a value of 10,000,000,000 for NaN and doesn't
| check if lat/long values are in range before calculating the average. It
| doesn't take very many 10 Billion values to really screw up the average
| :-) I modified gpsprof to toss out invalid lat/long values.

OK makes a lot of sense :-)

| Additional test results (from 20080802) are up at
| http://www.millions.ca/~stacy/neoFreeRunner/gpstale.html
|
| I did some more testing yesterday after compiling the latest version of
| GPSD for the FreeRunner (it no longer dies when I spam the SDCard...
| that's progress :-) but have not yet got the results pulled together.

Doesn't look a million miles away from being right... there are two
outliers shown and I guess the filtered  NaN(s), but basically all the
other samples are in a decent place.

- -Andy
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Re: Warranty after fix for GTA02 GPS rework for SD card interference issue

2008-08-05 Thread -stacy

Andy Green wrote:

| Has anyone
| figured out how to kick the GPS receiver into UBX mode? I would be
| curious to see if that changes anything.

It's actually documented by Ublox in here (Okular eats it)

http://www.u-blox.com/customersupport/gps.g3/ANTARIS_Protocol_Specification(GPS.G3-X-03002).chm

I've been reading that, but have not had any success in getting any UBX
output... I have managed to disable NMEA (both using $PUBX NMEA
extensions and your UBX generator) but then I get no data on the tty.

| Additional test results (from 20080802) are up at
| http://www.millions.ca/~stacy/neoFreeRunner/gpstale.html

Doesn't look a million miles away from being right... there are two
outliers shown and I guess the filtered NaN(s), but basically all the
other samples are in a decent place.

Atleast one of the outliers had multiple samples, but I am suspicious of
those being synthetic as well.

From the bit of testing I have done so far, it would seem that heavy
use of the SDCard can cause the CEP to increase by 25%-50% but it is
still typically better than the reference receivers. I had hoped to do
my next round of testing in UBX mode (if that solves the issue with
samples coming faster than once a second). If I can't get that figured
out soon, I will just configure the GPS to only emit GGA sentences, then
I will only get one fix per second from gpsd.

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