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 "Jet Lag" for SiRFstarIII <3.1.1 and Indoor Fix
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Squaredancer

284 Posts

Posted - 26 avr. 2005 :  06:27:24  Show Profile  Reply with Quote
I just returned to VA from NY via airplane. I used the BT-338 successfully in NY and partially during my flight, tracking the plane.

However, on the ground in VA, I have been unable to get a sat lock. I must have really confused it, with the last fix being at 26,000 ft at 435 MPH over PA, and then asking it to get a good fix quick in VA. I sat stationary for about 15 min in the airport parking lot with it on the roof, but it wasn't able to lock. I left it connected and on for 2+ hours, and still no lock. Turned it off for another couple of hrs, and now, at last check with VisualGPS, I have 12 Sats in view, but using NONE.
Looking at VisualGPS, I have 6 satellites with a level greater than the 28dbm minimum, with 3 of them being above 40 dbm, and still no lock. I'm going to turn it off overnite, and hope that in the morning, it will re-establish it's fix. If not, what do I do next? Would SIRFdemo help to re-establish the connection? And, with Auto-off, how do I drain the battery?

Edited by - Squaredancer on 26 avr. 2005 06:44:45

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gpspassion

93939 Posts

Posted - 26 avr. 2005 :  12:58:50  Show Profile  Visit gpspassion's Homepage  Reply with Quote
This is interesting as I have just gotten off a transatlantic flight myself, as well as walked around Manhattan these past few days and I'm under the impression that the BT-338 or more likely the current firmware of the SiRFstarIII chipset has some issues with working in difficult conditions (urban canyons, high altitude flying behind "coated portholes") and then getting "back on its feet". The fix I've found is to send a "cold reset" command to clear out the memory (mostly ephemeris data) and then it will get a fix in the usual 45/60 seconds.

Could you :
1. Look up the firmware version with SiRFdemo, see tutorial here http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=25575
2. Log maybe 5 minutes of data with VisualGPS with a good view of the sky
3. Send a Cold Reset command with SiRFdemo, see tutorial
4. Log 5 more minutes
5. Send me the logs on info [@] gpspassion.com
We can take it from there

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Marvin Hlavac

Canada
6904 Posts

Posted - 26 avr. 2005 :  13:20:20  Show Profile  Visit Marvin Hlavac's Homepage  Reply with Quote
I wonder if removing the battery for a minute would help, too.

Marvin Hlavac - Toronto, Canada
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gpspassion

93939 Posts

Posted - 26 avr. 2005 :  14:03:11  Show Profile  Visit gpspassion's Homepage  Reply with Quote
No that likely would not clear out the data in the same way a "cold reset" does as the SiRF chipsets have a backup battery that generally lasts for a week or so, still worth trying of course, although neither a cold reset or a trick like this should be required. The Xtrac v2 GPS I had with me did not have this problem.

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Squaredancer

284 Posts

Posted - 26 avr. 2005 :  16:14:42  Show Profile  Reply with Quote
Sorry gentlemen, but I used Winfast CE Navigator and did the same thing. I changed the CE setting to cold start and the BT-338 got the fix about 45 seconds later. I'm sorry that I couldn't give you the logs for you to check, but I will be flying again in October and will get the logs if it happens again.
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gpspassion

93939 Posts

Posted - 26 avr. 2005 :  16:24:14  Show Profile  Visit gpspassion's Homepage  Reply with Quote
Sure that's not a problem, I should be able to recreate it now that I know what to look for. There's some "looping" going on it seems with possibly new ephemeris data not getting downloaded properly until the old one is "flushed out" by the cold reset.

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Squaredancer

284 Posts

Posted - 27 avr. 2005 :  04:08:29  Show Profile  Reply with Quote
quote:
Originally posted by Carl@Sirf on 4/8

Most receivers track in real time, meaning as the stream of 1s and 0s come in from the RF section, the hardware assigned to track a satellite compares that incoming stream with another stream created inside the receiver and adjusted to match what that satellite should be sending. When the streams match sufficiently, we have a track.


_________________________________________________________________________
I wonder if the above is the source of the problem? Above was taken from the discussion on Satellites vs Channels in the SirfDemo Tutorial Thread.
Since the last known fix was hundreds of miles away from the current location, if the chip is comparing the new data to the outdated data, there will be now match. It might be discarding the new data and trying to get a match with the old info which won't happen. It could be that there is a "glitch" in the logic when it compares the stored vs the new data. Since it's not often that the stored info is 100's of miles away from the new info, it could have escaped the programmers.
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Carl@SiRF

USA
159 Posts

Posted - 28 avr. 2005 :  17:28:49  Show Profile  Reply with Quote
The suggestion by Squaredancer that the stored information is outdated is not possible. The data in the 20 ms buffers is always no older than 20 ms, and the patterns generated internally represent the 1 ms PRN sequence each satellite generates and repeats continuously. The only effect the previous solution might have on the attempt at a current solution would come in the prediction of the where to look for the new data stream, and the fact that the receiver finds the satellites and downloads their ephemerides indicates that portion is working fine. I won't speculate on what might be causing this glitch, but we will investigate.

Carl - SiRF Customer Support
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karhill

94 Posts

Posted - 28 avr. 2005 :  22:02:08  Show Profile  Reply with Quote
I noticed something similar with a new Globalstat Bt-338. After an abrupt change in altitude the BT-338 refused to get a fix. I turned the BT-338 on before the start of hike...it generated a proper fix very quickly, like normal. It had reception from all visable satellites. I then turned the BT-338 off and climbed about 2000 feet before turning the BT-338 back on. At that point, it refused to get a fix, even when left on for about an hour from the same spot. The satellite observation dialog box for my application showed the satellites in all the proper positions (very similar to the fix at the start of the hike) - as if the BT-338 had almanac information, but all the satellites were red rather than blue, which in the application (Oziexplorer CE) means no signal, I believe (or else no emphemeris data yet). The BT-338's view of the sky during this hour period was such that at least some of the overhead birds should have been coming in loud and clear.

When I returned to the elevation of the start of hike and restarted the BT-338, a proper fix was obtained in short order. However, GpsInfo shows that the BT-338, while reporting the correct time, reports a data of 2085/09/12!
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Carl@SiRF

USA
159 Posts

Posted - 28 avr. 2005 :  22:20:20  Show Profile  Reply with Quote
Seeing this problem with a large change in altitude is good information -- I will pass it on. I wonder if your receiver sait 2085/09/12 or just 85/09/12. The difference is that 1985 is what the date would be if the receiver thought it was first cycle of GPS weeks rather than the current second cycle (1985/09/12 + 1024 weeks = 2005/04/28). Please let me know if that is possible.

And if anyone else sees these problems (receiver won't report a fix after it apparently acquires several satellites, or reports a wildly bad date), record as much information as you can, then try restarting the receiver. Send your information to your supplier and ask that they relay it to SiRF. Thanks.

Carl - SiRF Customer Support
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gpspassion

93939 Posts

Posted - 28 avr. 2005 :  22:28:56  Show Profile  Visit gpspassion's Homepage  Reply with Quote
Altitude was not a factor in my case, at least not a change in altitude. I will try to look at my logs recorded on my flight from Paris to NYC , cruising at 30,000 feet and at 500knots, it was quite odd to see SS3 (BT-338) and XT2 (RBT-1000) get a fix after being placed against the window, keep it when placed on the side, lose it when placed on the tablet and then XT2 gettin it back when placed back next to the window but SS3 requiring a cold reset to get back on its feet. I was a bit puzzled naturally ;-)

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karhill

94 Posts

Posted - 29 avr. 2005 :  07:00:34  Show Profile  Reply with Quote
quote:
Originally posted by Carl@SiRF

Seeing this problem with a large change in altitude is good information -- I will pass it on. I wonder if your receiver sait 2085/09/12 or just 85/09/12. The difference is that 1985 is what the date would be if the receiver thought it was first cycle of GPS weeks rather than the current second cycle (1985/09/12 + 1024 weeks = 2005/04/28). Please let me know if that is possible.
Carl - SiRF Customer Support


The date reported by my BT-338 (as reported by the GPS Info PocketPC application that ships with the BT-338) was definately 2085/09/12. But I think you are on to something...it might really be 1985, but GPS Info is reporting as 2085. Or something else along your line of thought. In the massive BT-338 thread (http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=19000&whichpage=26) there were several other reports of dates in 2085 being reported by the BT-338. The actual dates all seem to fit your x + 1024 formula.
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kenyee

201 Posts

Posted - 29 avr. 2005 :  17:13:28  Show Profile  Reply with Quote
That sounds like my "start it in the glovebox and it never locks, even if you take it out" symptom...

Power cycling fixes it in my case...
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Steve672

102 Posts

Posted - 13 mai 2005 :  17:12:04  Show Profile  Reply with Quote
GPSPassion, you have tested several GPSs with the SiRFstarIII chipset.
1. Are they all prone to this problem?
2. Do you know the cause.
3. Has it been fixed?
4. If it occurs, is there a consensus on how to fix it (cold reset, SirfDemo, power cycling...)?
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gpspassion

93939 Posts

Posted - 13 mai 2005 :  17:18:02  Show Profile  Visit gpspassion's Homepage  Reply with Quote
1. Not, but then I have only flown with the 338 so far. I thought I had it happen again the other day with the 338 as mentioned above but I am not certain at this point. I have a long flight planned at the end of the month so I will test again, with the other receivers this tims.
2. No
3. Not that I know of
4. Cold reset yes.

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Carl@SiRF

USA
159 Posts

Posted - 13 mai 2005 :  17:58:09  Show Profile  Reply with Quote
We know the cause now, and will release new code very shortly that addresses it as well as a couple other "nuisance" type bugs at the same time. Look for 3.1.1 release within a few days.

Carl - SiRF Customer Support
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