GPS Problems

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(Added more fix information from mailing list)
m (Capacitor also on 20080723)
 
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See [[GPS]] for details on how to evaluate the Freerunner GPS with command line utilities.
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See GPS for details on how to evaluate the [[Neo FreeRunner GPS]] with command line utilities.
  
== MicroSD Card Issue ==
+
=== Problem: it takes a long time (10min+) before the FreeRunner gets first GPS data ===
  
[http://lists.openmoko.org/pipermail/community/2008-July/021774.html This thread] indicates that the problem is interference from the SD card slot, and recommends trying without the SD card inserted. A [http://lists.openmoko.org/pipermail/openmoko-kernel/2008-July/003777.html software workaround] is under testing...
+
It was found that the Openmoko FreeRunner GPS has a long Time To First Fix (TTFF) when there is an SD card in the phone. [http://lists.openmoko.org/pipermail/community/2008-July/021774.html This thread] indicates that there is interference from the SD card slot: TTFF is much shorter without an inserted SD card.
  
=== Summary ===
+
::More specific: the GPS signal level drops by 20dB, i.e. a factor of 100. Signal strength of a GPS satellite above your head is around -127dBm. Needed strength for a first fix is -145dBm with a minimum of three satellites. Once the GPS chip has a fix, it can operate at signal levels of -157dBm, thus making it possible to operate while there is data transfer from/to the SD card.
Alasal posted a summary of the SD/GPS issue to the community mailing list (http://lists.openmoko.org/pipermail/community/2008-July/022180.html). The following is a wikified version of that summary, edited for clarity and to keep up with changing information.
+
::''(From http://lists.openmoko.org/pipermail/community/2008-July/022202.html )''
  
;Summary of the summary
+
=== Solutions ===
:You will be able to use the SD card at the same time as the GPS except for the first approximately 30 seconds. (And that's the worst case, because maybe OpenMoko can find better hacks/fixes).
+
  
;Do the people of OpenMoko know about the problem?
+
{{Note|It seems that in the newer version of the hardware, a compensating capacitor is now present. So this problem should be fixed with newer devices. First noticed on 20080724 and confirmed on 20080830. You can check if it has the fix by looking for the capacitor beneath the SD card, as shown in [[Media:Gta02 gps 10pf rework sop.pdf|this PDF file]].}}
:Yes.
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{{Note|The capacitor also appeared on a 20080723 purchased from Pulster vendor.}}
  
;Are they working on the problem?
+
A [http://lists.openmoko.org/pipermail/openmoko-kernel/2008-July/003777.html software workaround] has been released as a kernel patch and may be acquired simply by doing an "opkg update" and "opkg upgrade" and then rebooting your FreeRunner. This workaround effectively turns off the SD card clock when the SD card is not being used. You can then use the SD card simultaneously with GPS, except for the first approximately 30 seconds.
:Yes, they are actively searching for a solution.
+
  
;What is the problem?
+
Openmoko is soliciting the assistance of the community to test the effectiveness of this software fix. The experiment consists of a series of measurements in different conditions, prior to applying the software fix and then after applying the software fix. Please visit [[FreeRunner GPS Software Fix TTFF Measurement Test]] for instructions to participate and to see the results so far of this test.
:The OpenMoko FreeRunner has a long TTFF with the SD card in the phone, so it takes a long time (10min+) before you get your first GPS data.
+
 
::More specific: the GPS signal level drops by -20dBm, i.e. factor 100. Signal strength of a GPS satellite above your head is around -127dBm. Needed strength for a first fix is -145dBm with a minimum of three satellites. Once the GPS chip has a fix, it can operate at signal levels of -157dBm, thus making it possible to operate while there is data transfer from/to the SD card.
+
Openmoko has examined a hardware solution: soldering a 10 pf capacitor between SD card pin 5 (clk) and pin 6 (Vss) [[Image:Gta02 gps 10pf rework sop.pdf]] and more detailed [[Image:SOP_for_GPS_capacitor_rework.pdf|GPS issue SD clcok pin capacitor rework guide]]. This effectively restores GPS performance to the levels obtained without the SD card inside. The rework is not suggested to end users without hardware soldering technique and equipment. This rework is done on all the new fabricated Neo FreeRunners
::''(From http://lists.openmoko.org/pipermail/community/2008-July/022202.html )''
+
 
 +
==== Hardware mod related ====
 +
 
 +
See:
 +
* [[Shop:Speedevil|Speedevil's Shop]] for a UK service to perform this operation on your freerunner, or globally shipped 10pF capacitor.
 +
 
 +
*  [http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=490-1278-1-ND Digikey] for the capacitor.
 +
 
 +
=== Discussion ===
 +
 
 +
The following is based on [http://lists.openmoko.org/pipermail/community/2008-July/022180.html Alasal's post] to the community mailing list.
  
 
;What is TTFF?
 
;What is TTFF?
:This is the time to first fix of the GPS. This is the time the GPS needs to get the first clue on where you are on planet earth. So you have to do this only once. After you have a FF (first fix), you can get more fixes without any problems with the SD card in the phone.
+
:TTFF means Time To First Fix of the GPS. This is the time the GPS needs to get the first clue on where you are on planet earth. So you have to do this only once. After you have a FF (first fix), you can get more fixes without any problems with the SD card in the phone.
 +
 
  
 
;So if we have a first fix, the SD card doesn't block the GPS anymore?
 
;So if we have a first fix, the SD card doesn't block the GPS anymore?
 
:Yes, the SD card doesn't block the GPS if we have a first fix. (Some people even claim it's more stable)
 
:Yes, the SD card doesn't block the GPS if we have a first fix. (Some people even claim it's more stable)
  
;Does the lower signal also effect accuracy?
+
 
 +
;Why do we need a first fix?
 +
: According to [http://lists.openmoko.org/pipermail/community/2008-July/020705.html Al Johnson], the Antares4 chip on the GTA02 doesn't have the memory needed to store almanac and ephemeris, last known position or time. This means that every start is a true cold start. It [http://lists.openmoko.org/pipermail/community/2008-July/020772.html is possible] to save location, almanac and ephemeris at GPS shut down, and restore these information at the next startup, but that does not seem implemented yet.
 +
 
 +
 
 +
;Does the lower signal also affect accuracy?
 
:It is a good deal more jittery. However, if you drive around in a city you will get a lot more error from signal reflections than from the jitter.
 
:It is a good deal more jittery. However, if you drive around in a city you will get a lot more error from signal reflections than from the jitter.
 
:''(From http://lists.openmoko.org/pipermail/community/2008-July/022209.html )''
 
:''(From http://lists.openmoko.org/pipermail/community/2008-July/022209.html )''
 +
  
 
;Do they have a solution?
 
;Do they have a solution?
Line 38: Line 53:
 
::''(From http://lists.openmoko.org/pipermail/community/2008-July/022242.html )''
 
::''(From http://lists.openmoko.org/pipermail/community/2008-July/022242.html )''
  
;Do we have to return our FreeRunners to OpenMoko?
+
 
 +
;Do we have to return our FreeRunners to Openmoko?
 
:Probably not, because the software workaround should work too.
 
:Probably not, because the software workaround should work too.
  
 
;But we can't read from the SD card when the GPS is on?
 
;But we can't read from the SD card when the GPS is on?
:Wrong, you will be able to read the SD card when the GPS is on. You will probably not be able to read the SD card when you're starting the GPS (approximately 30 seconds), because the SD card only stops the GPS from getting its first fix. After that you will be able to read the SD card again.
+
:Wrong, you will be able to read the SD card when the GPS is on. The clock for the SD card used to run constantly.  Now the kernel turns it off when the SD card is not in use. As long as you are not constantly reading from the SD card, you should see much better first fix times. Obtaining a GPS fix does not affect SD performance.
 
+
;Is there a better software solution?
+
:Maybe. From reading the mailing list, I have understood that half the Openmoko team is looking into this bug. All this information is only 1 - 2 days old and the bug is also young, so I suspect they can fine-tune the software workaround and make it only slow down the SD card or even better.
+
  
 
;Did Openmoko test the GPS with a SD card in it?
 
;Did Openmoko test the GPS with a SD card in it?
 
:Yes.
 
:Yes.
  
;Whey didn't they find it while testing the Freerunner?
+
;Why didn't they find it while testing the FreeRunner?
 
:Because they have to do the tests with a fake GPS signal and with that signal it worked (In a fab you don't have a decent GPS signal). They have already modified the test, so it corresponds to the GPS signal better.
 
:Because they have to do the tests with a fake GPS signal and with that signal it worked (In a fab you don't have a decent GPS signal). They have already modified the test, so it corresponds to the GPS signal better.
 
  
 
== Information about faulty antennas ==
 
== Information about faulty antennas ==
  
* If you removing the SD card doesn't help and you suspect your antenna, try unplugging and replugging the internal GPS connector. (See [[Disassembling_Neo1973]] about 2/3 of the way down.  (this may differ on freerunner, pictures appreciated)
+
* If removing the SD card doesn't help and you suspect your antenna, try unplugging and replugging the internal GPS connector. (See [[Disassembling_Neo1973]] about 2/3 of the way down.  (this also applies to the Freerunner, since it's the same case)
Also note that there is a trac ticket for this issue: [http://docs.openmoko.org/trac/ticket/1542 #1542]
+
 
 +
* Also note that there is a trac ticket for this issue: [http://docs.openmoko.org/trac/ticket/1542 #1542]
  
[[FreeRunner_GPS_antenna_repair_SOP]] Indicates that some (rare?) units may have bad soldering, and includes a guide to fix. This will presumably void your warranty.
+
* [[FreeRunner GPS antenna repair SOP]] indicates that some (rare?) units may have bad soldering, and includes a guide to fix. This will presumably void your warranty.
  
[[Category:GPS]]
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[[Category:Neo FreeRunner solved GPS problems]]

Latest revision as of 13:31, 15 September 2009

See GPS for details on how to evaluate the Neo FreeRunner GPS with command line utilities.

Contents

[edit] Problem: it takes a long time (10min+) before the FreeRunner gets first GPS data

It was found that the Openmoko FreeRunner GPS has a long Time To First Fix (TTFF) when there is an SD card in the phone. This thread indicates that there is interference from the SD card slot: TTFF is much shorter without an inserted SD card.

More specific: the GPS signal level drops by 20dB, i.e. a factor of 100. Signal strength of a GPS satellite above your head is around -127dBm. Needed strength for a first fix is -145dBm with a minimum of three satellites. Once the GPS chip has a fix, it can operate at signal levels of -157dBm, thus making it possible to operate while there is data transfer from/to the SD card.
(From http://lists.openmoko.org/pipermail/community/2008-July/022202.html )

[edit] Solutions

NOTE: It seems that in the newer version of the hardware, a compensating capacitor is now present. So this problem should be fixed with newer devices. First noticed on 20080724 and confirmed on 20080830. You can check if it has the fix by looking for the capacitor beneath the SD card, as shown in this PDF file.


NOTE: The capacitor also appeared on a 20080723 purchased from Pulster vendor.


A software workaround has been released as a kernel patch and may be acquired simply by doing an "opkg update" and "opkg upgrade" and then rebooting your FreeRunner. This workaround effectively turns off the SD card clock when the SD card is not being used. You can then use the SD card simultaneously with GPS, except for the first approximately 30 seconds.

Openmoko is soliciting the assistance of the community to test the effectiveness of this software fix. The experiment consists of a series of measurements in different conditions, prior to applying the software fix and then after applying the software fix. Please visit FreeRunner GPS Software Fix TTFF Measurement Test for instructions to participate and to see the results so far of this test.

Openmoko has examined a hardware solution: soldering a 10 pf capacitor between SD card pin 5 (clk) and pin 6 (Vss) File:Gta02 gps 10pf rework sop.pdf and more detailed File:SOP for GPS capacitor rework.pdf. This effectively restores GPS performance to the levels obtained without the SD card inside. The rework is not suggested to end users without hardware soldering technique and equipment. This rework is done on all the new fabricated Neo FreeRunners

[edit] Hardware mod related

See:

  • Speedevil's Shop for a UK service to perform this operation on your freerunner, or globally shipped 10pF capacitor.

[edit] Discussion

The following is based on Alasal's post to the community mailing list.

What is TTFF?
TTFF means Time To First Fix of the GPS. This is the time the GPS needs to get the first clue on where you are on planet earth. So you have to do this only once. After you have a FF (first fix), you can get more fixes without any problems with the SD card in the phone.


So if we have a first fix, the SD card doesn't block the GPS anymore?
Yes, the SD card doesn't block the GPS if we have a first fix. (Some people even claim it's more stable)


Why do we need a first fix?
According to Al Johnson, the Antares4 chip on the GTA02 doesn't have the memory needed to store almanac and ephemeris, last known position or time. This means that every start is a true cold start. It is possible to save location, almanac and ephemeris at GPS shut down, and restore these information at the next startup, but that does not seem implemented yet.


Does the lower signal also affect accuracy?
It is a good deal more jittery. However, if you drive around in a city you will get a lot more error from signal reflections than from the jitter.
(From http://lists.openmoko.org/pipermail/community/2008-July/022209.html )


Do they have a solution?
Yes. There is already a highly alpha software workaround. The software just turns off the SD card clock when the SD card is not being used. They are also examining a hardware solution.
The software fix is still in testing. Expect first results this noon (Thursday, 17th July 2008) (Taipeh time).
Also, the hardware fix needed is rather easy. No need to open the shielding or housing. We are working on a document which gives you detailed instructions.
(From http://lists.openmoko.org/pipermail/community/2008-July/022242.html )


Do we have to return our FreeRunners to Openmoko?
Probably not, because the software workaround should work too.
But we can't read from the SD card when the GPS is on?
Wrong, you will be able to read the SD card when the GPS is on. The clock for the SD card used to run constantly. Now the kernel turns it off when the SD card is not in use. As long as you are not constantly reading from the SD card, you should see much better first fix times. Obtaining a GPS fix does not affect SD performance.
Did Openmoko test the GPS with a SD card in it?
Yes.
Why didn't they find it while testing the FreeRunner?
Because they have to do the tests with a fake GPS signal and with that signal it worked (In a fab you don't have a decent GPS signal). They have already modified the test, so it corresponds to the GPS signal better.

[edit] Information about faulty antennas

  • If removing the SD card doesn't help and you suspect your antenna, try unplugging and replugging the internal GPS connector. (See Disassembling_Neo1973 about 2/3 of the way down. (this also applies to the Freerunner, since it's the same case)
  • Also note that there is a trac ticket for this issue: #1542
Personal tools

See GPS for details on how to evaluate the Freerunner GPS with command line utilities.

MicroSD Card Issue

This thread indicates that the problem is interference from the SD card slot, and recommends trying without the SD card inserted. A software workaround is under testing...

Summary

Alasal posted a summary of the SD/GPS issue to the community mailing list (http://lists.openmoko.org/pipermail/community/2008-July/022180.html). The following is a wikified version of that summary, edited for clarity and to keep up with changing information.

Summary of the summary
You will be able to use the SD card at the same time as the GPS except for the first approximately 30 seconds. (And that's the worst case, because maybe OpenMoko can find better hacks/fixes).
Do the people of OpenMoko know about the problem?
Yes.
Are they working on the problem?
Yes, they are actively searching for a solution.
What is the problem?
The OpenMoko FreeRunner has a long TTFF with the SD card in the phone, so it takes a long time (10min+) before you get your first GPS data.
More specific: the GPS signal level drops by -20dBm, i.e. factor 100. Signal strength of a GPS satellite above your head is around -127dBm. Needed strength for a first fix is -145dBm with a minimum of three satellites. Once the GPS chip has a fix, it can operate at signal levels of -157dBm, thus making it possible to operate while there is data transfer from/to the SD card.
(From http://lists.openmoko.org/pipermail/community/2008-July/022202.html )
What is TTFF?
This is the time to first fix of the GPS. This is the time the GPS needs to get the first clue on where you are on planet earth. So you have to do this only once. After you have a FF (first fix), you can get more fixes without any problems with the SD card in the phone.
So if we have a first fix, the SD card doesn't block the GPS anymore?
Yes, the SD card doesn't block the GPS if we have a first fix. (Some people even claim it's more stable)
Does the lower signal also effect accuracy?
It is a good deal more jittery. However, if you drive around in a city you will get a lot more error from signal reflections than from the jitter.
(From http://lists.openmoko.org/pipermail/community/2008-July/022209.html )
Do they have a solution?
Yes. There is already a highly alpha software workaround. The software just turns off the SD card clock when the SD card is not being used. They are also examining a hardware solution.
The software fix is still in testing. Expect first results this noon (Thursday, 17th July 2008) (Taipeh time).
Also, the hardware fix needed is rather easy. No need to open the shielding or housing. We are working on a document which gives you detailed instructions.
(From http://lists.openmoko.org/pipermail/community/2008-July/022242.html )
Do we have to return our FreeRunners to OpenMoko?
Probably not, because the software workaround should work too.
But we can't read from the SD card when the GPS is on?
Wrong, you will be able to read the SD card when the GPS is on. You will probably not be able to read the SD card when you're starting the GPS (approximately 30 seconds), because the SD card only stops the GPS from getting its first fix. After that you will be able to read the SD card again.
Is there a better software solution?
Maybe. From reading the mailing list, I have understood that half the Openmoko team is looking into this bug. All this information is only 1 - 2 days old and the bug is also young, so I suspect they can fine-tune the software workaround and make it only slow down the SD card or even better.
Did Openmoko test the GPS with a SD card in it?
Yes.
Whey didn't they find it while testing the Freerunner?
Because they have to do the tests with a fake GPS signal and with that signal it worked (In a fab you don't have a decent GPS signal). They have already modified the test, so it corresponds to the GPS signal better.


Information about faulty antennas

  • If you removing the SD card doesn't help and you suspect your antenna, try unplugging and replugging the internal GPS connector. (See Disassembling_Neo1973 about 2/3 of the way down. (this may differ on freerunner, pictures appreciated)

Also note that there is a trac ticket for this issue: #1542

FreeRunner_GPS_antenna_repair_SOP Indicates that some (rare?) units may have bad soldering, and includes a guide to fix. This will presumably void your warranty.