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gpspassion

93964 Posts

Posted - 20 mars 2005 :  16:36:53  Show Profile  Visit gpspassion's Homepage  Reply with Quote
UPDATED20101201
SiRFdemo for PCs (and PocketPCs*)
Advanced configuration for SiRF based GPS receivers!



>> SORRY THE PICTURES HAVE BEEN LOST
EXPLANATIONS SHOULD STAND BY THEMSELVES
IF NOT FEEL FREE TO ASK ANY QUESTIONS <<


Before proceeding, download the latest version of SiRFdemo
PC Version (advanced) : v3.87 - PPC Version (basic): v1.16



INDEX

  1. Introduction
  2. Configuration
  3. Navigation Parameters
  4. Configuring 'Static Navigation'
  5. Back to NMEA
  6. Links of interest


1. INTRODUCTION



Why use SiRFdemo ?
  1. To take a peek at the advanced settings of your GPS receiver and to see how it was set in the factory, or modify some of these settings

  2. Your GPS is behaving oddly and you want to reset it to factory defaults

  3. You want to verify the revision of the Firmware loaded on your GPS receiver - (insight on SiRF FW naming)

<!> Beware <!>
While using this software will normally not damage your receiver, please realize that some actions not covered in this tutorial might misconfigure your receiver and likely void your warranty. In any case, GpsPasSion will not be held responsible if your GPS receiver stops responding from the use of this software



2. CONFIGURATION


  1. To use SiRFdemo you need a PC or a laptop and a way to connect your GPS receiver. For a compact flash GPS, you can use a PCMCIA/CF adapter, for a wired GPS, a DB9 serial port or USB via a USB/DB9 adapter and of course a Bluetooth GPS receiver with built-in BT or a dongle
  2. You need to identify the correct COM port used by your GPS. It will be COM1 for a serial GPS generally and for a Bluetooth GPS, a right click on the connection will show you the port
  3. Launch SiRFdemo - choose the correct COM port and select 4,800 (or 38,400 for a Bluetooth GPS) (fig 1)
  4. SiRFdemo only provides detailed information in SiRF mode so do \Action\Switch to SiRF (fig 2) and you will see the various windows "light up"(fig 3)


Fig.1 Fig.2 Fig.3



3. NAVIGATION PARAMETERS


A modern GPS receiver is a full blown "computer" equipped with a CPU - baseband chip (ARM), an RF chip (signal processing), ROM (rewritable flash) and RAM - but unlike a "normal" computer it is highly specialized and has been programmed accordingly. Some of these parameters are visible as the "Navigation Parameters"; to make them appear in the "Response View" window, do \Poll\Navigaton Parameters. Let's take a brief look at them :


Fig.4 Fig.5


  1. Operating Mode (Degraded/Altitude Hold/Dead Reckoning) : défines the operating mode when optimal reception (4+ satellites) is no longer available
  2. Track Smoothing : wrill smoothen the track to remove the "jumps" resulting from the natural "inaccuracy" of the GPS system (10/15 meters) - disabled by default
  3. Static Navigation : will "freeze" the position at very low speed to cancel out the drifting resulting from the natura "inaccuray" of GPS - should be disabled for pedestrian use - see below for details
  4. DOP : filtering based on the quality of reception
  5. DGPS : controls the activation of SBAS (WAAS in the US and EGNOS in Europe) - since SA (Selective Availability) was removed in May 2000, mainly useful to check the integrity of the GPS signal for critical use in planes and in shipts - available on SiRFstar III with FW 3.1 and above
  6. Power : to configure power saving trickle modes

Note : To show the firmware version loaded in your GPS in the top window, do \Poll\SW Version - GSW3.0...with the SiRFIII Globalsat BT-338 GPS I was using.


4. STATIC NAVIGATION


While most settings are best left untouched unless you want to experiment (always risky !), "Static Navigation" is one that should be looked at closely especially with the arrival of the new SiRFstarIII based receivers, as these ultra-powerful receivers take GPS reception to a new level and can work with very weak signals but when that happens, accuracy can be impacted. Observations over a 24 hour period show that with good signals, 95% of the positions reported by the GPS will be within a 15 meter radius, while with weak signals, 95% of the positions will be within a radius of 50 meters.

Current road navigation software is designed for GPS receivers that only operate with good signals so accuracy will be in the 15 meter area. Such software will "snap" the position to the closest road so in a dense urban area, with degraded accuracy it's going to be easy to make the wrong decision and produce "uncosmetic" results and possibly force a trip recalculation.

Instead of redesigning navigation software to take this account (one could imagine some type of dynamic filtering based on DOP) and risk increasing the processing load on the PDA and hurt user experience, the easy fix is to implement this fix directly by having GPS manufacturers activate "Static Navigation" by default and therefore freeze the position using some complex algorithms mainly speed dependent. The problem with this is that this will considerably hurt low speed pedestrian use, with the speed staying on "0" and 50 meter jumps (update threshhold). If you want to use your GPS receiver outside your car, you'll need to disable SN, this is how to do it :


Fig.6 Fig.7


  1. \Navigation\Static Navigation\ (fig. 6)
  2. Click on "Disable" then SEND (fig. 7)
  3. Verify that the change has been recorded by the GPS by calling the Navigation Parameters
  4. Please note that the default setting will return with a "factory reset" command or when the battery runs out
  5. Analyzing: As you can see in 9a, representing a walk with silumtaneaous logging, the impact of SN on a SiRFstarIII GPS is pretty significant, better accuracy, better distance measurement, with Xtrac 2 there is no notable impact and its status as a "non-pedestrian" friendly GPS remains.


BEFORE - AFTER - On the Field

Fig.8 Fig.9 Fig.9a



5. BACK TO NMEA


NMEA being the universal GPS language, best not to forget to return to that mode after looking up the advanced settings and possibly modifying them. There are two ways to proceed:
  1. To keep your settings : \Action\Switch to NMEA Protocol\ select 4,800 then Send (fig. 10 et 11)
  2. To set your GPS back to its factory settings : \Action\Initialize Data Source\Factory Reset then Send (fig. 12 et 13)


Fig.10 Fig.11

Fig.12 Fig.13



6. USEFUL LINKS


  1. "Technical Forums" - >>HERE<<


* PocketPC owners can also try this application that I have found to work as well although not with WM2003SE. For WM2003SE you can use this program to toggle SN and also or CE Monitor and GPSTweak for SBAS settings - 02/2006 : here is a new "tweaker", SiRFtech.

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bluetoothwantabe

28 Posts

Posted - 26 mars 2005 :  08:35:36  Show Profile  Reply with Quote
just want to report that this software may not 100% compatible with fountna/belkin bluetooth gps(xtrac2). everything works as expected up to step 5. Yes, i did select 4800 for baud rate. 5a results in repeated error message "comm: unknown char: 80" in "Error View", i have to reset the device by taking the battery out to make it function agains. On the other hand, 5b works just fine. This is annoying as i would like to use it for geocaching and that "static naviagtion" feature simply kills it.

Edited by - bluetoothwantabe on 26 mars 2005 08:38:54
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gpspassion

93964 Posts

Posted - 26 mars 2005 :  11:28:16  Show Profile  Visit gpspassion's Homepage  Reply with Quote
Good point, try switching back to NMEA/38,400 first as I think it doesn't like the simultaneous protocol/speed switch - switching to SiRF isn't a problem is it in 2.4 ? If it works please report back on the impact for geocaching, as I'm not positive it will help a lot going by the testing I did above.

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Leif

Sweden
141 Posts

Posted - 26 mars 2005 :  23:07:53  Show Profile  Reply with Quote
I found some static navigation info in SiRF's own faq.

http://www.sirf.com/techlibrary/FAQs/FAQs.html

SiRFStarII Software

93. Explain the static navigation parameters.

Since SA was turned off, we now disable static navigation as our default, and we recommend that you do also. When it is enabled, if velocity is below 1.2 m/s for 3 seconds we will freeze the position, and leave them frozen until velocity exceeds 1.4 m/s (so there is a bit of hysteresis in the solution).

123. What criteria are used to enable and disable the static navigation filter?

Static navigation is a mode designed for motor vehicles, which causes the position to become pinned at one location when velocity is determined to be low enough. This is designed to make navigation systems operate more reasonably when the GPS Selective Availability (SA) signal degradation is turned on. When the navigation software determines that the vehicle velocity is less than 1.2 m/s for 3 seconds, the position is pinned to its current position. It remains pinned until either velocity is detected above 1.4 m/s, or position is computed to be 200 m from the pinned location.
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gpspassion

93964 Posts

Posted - 26 mars 2005 :  23:57:07  Show Profile  Visit gpspassion's Homepage  Reply with Quote
Interesting find, although this seems to date a bit given the refrence to SA I wonder if it wouldn't apply to SiRFtarI in any case the principle is still there and has been revisited with SiRF working with much lower signal than previous generations.

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Carl@SiRF

USA
159 Posts

Posted - 29 mars 2005 :  19:38:19  Show Profile  Reply with Quote
Two responses for this forum: with Bluetooth GPS units, often the Bluetooth modem only handles 1 baud rate. So to switch protocol, be sure to specify the same baud rate as used in the current protocol.

For Static Navigation, there are different limits depending on the particular software version. Some freeze at 1.2 m/s and unfreeze at about 1.4 m/s or 200 m movement; others freeze at 0.8 m/s and unfreeze at about 9.6 m/s or 50 m movement. Other limits may exist in some other builds.

Carl - SiRF Customer Support
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gpspassion

93964 Posts

Posted - 29 mars 2005 :  19:50:02  Show Profile  Visit gpspassion's Homepage  Reply with Quote
Welcome to the forums, Carl !
1. Yes I meant to adjust the 4,800 to 38,400 upon connection as this seems to be the "natural" baudrate of many Bluetooh GPS receivers and happens to be the baudrate chosen by SiRFdemo with "Switch to SiRF" so that prevents the simultaneous baudrate/protocol switching that BT GPS receivers don't like.

2. Are you referring to SiRFIII software versions or SiRF chipsets in general? Is there a way of finding out from within SiRfdemo? 9.6m/s seems pretty high in the second setup, that's about 30kph, I don't believe I've ever seen that type of "drifting speed" even when the GPS is working with very low signal?

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Carl@SiRF

USA
159 Posts

Posted - 29 mars 2005 :  21:28:07  Show Profile  Reply with Quote
Sorry for a typo -- I meant 0.96. The actual value for turn off based on velocity is the square root of 1.2 times the turn-on velocity squared. So if turn on is 0.8 m/s, then turn off is sqrt(0.8 * 0.8 * 1.2) = 0.876, or closer to 0.9. For 1.2 m/s turn on, that works out to 1.314 m/s.

This formula works in all SS2 (including Xtrac) and SS3 code. The specific values used depend on the individual code. Within any one platform (SS2, SS3, Xtrac) there can be multiple settings depending on the version and on individual customer builds.

Carl - SiRF Customer Support
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bluetoothwantabe

28 Posts

Posted - 30 mars 2005 :  06:28:46  Show Profile  Reply with Quote
i got it working! it appears that the bluetooth gps i have(belkin, rebadged fouturna clipon) is only capable of switching mode at 38400. So what i had to do was using baud rate 38400 in both step 2.3 and 5a. It’s interesting that it actually partially works under 4800. Maybe it has a compatibility mode built-in as most software’s use/require 4800 by default? I just looked up the definition of "Baud Rate", my understanding is that bigger number indicates greater potential transmission capability(aka. bandwidth), right?

Anyhow, I am so happy!

BTW, i just notice one fascinating message in the "Debug View" during my switch from SiRF to NMEA: "$PSRFTXT,Baud rate: 38400 System clock:24.553Mhz*45"
Is the second part the actual speed of the processor inside my gps? and does "*45" part mean i should multiple 45 to 24.553 to get the overall speed or does it mean something completely different?

Edited by - bluetoothwantabe on 30 mars 2005 06:32:20
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Carl@SiRF

USA
159 Posts

Posted - 30 mars 2005 :  11:13:38  Show Profile  Reply with Quote
Glad to hear you got it working. No doubt that modem only works at 38400.

Baud rate is really the rate of bit transitions on the serial data link. Since each byte of data adds a start and stop bit, it is 10 bits long, and 38400 baud is 3840 bytes per second. Faster bit rates transfer more bytes per second, i.e., greater bandwidth.

That text line you saw is called a proprietary message. All NMEA messages begin with $. The P means a proprietary message, SRF is the 3-character code assigned by NMEA to SiRF. The text that follows is all free-form under NMEA, and can be whatever we want it to be. In this case it is telling you your serial port baud rate and the CPU clock speed. The *45 is the checksum (exclusive OR of all characters after the $ and before the *).

Carl - SiRF Customer Support
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Leif

Sweden
141 Posts

Posted - 30 mars 2005 :  20:42:44  Show Profile  Reply with Quote
I would also like to disable static navigation on my GPS. Problem is that I have a Yakumo delta 300 GPS (rebadged Mitac Mio 168) PocketPC with integrated GPS. Firmware 2.4.12.09-XMitac-C4PROD2.0 0000003729. The only GPS interface is internal to PocketPC COM2.

Is there a version of the SiRFXTracDemo PocketPC program, that used to be available for download from SiRF, that is updated to change the static navigation setting?
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gpspassion

93964 Posts

Posted - 30 mars 2005 :  20:48:35  Show Profile  Visit gpspassion's Homepage  Reply with Quote
You need to get access from a PC so I can't think of a way to change that setting, such tools don't exist for PocketPCs, besides you can see in the example above that Xtrac v2 doesn't seem to benefit much from SN disabling.

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Carl@SiRF

USA
159 Posts

Posted - 31 mars 2005 :  05:55:16  Show Profile  Reply with Quote
Actually there is a product called SiRFDemoPPC that provides at least some of the features of SiRFDemo for the Pocket PC environment. Contact your SiRF rep to request a copy. Unfortunately I don't have a PPC platform to use to see if the feature you want is there, and the manual for it is not yet published. You'll need to experiment.

Carl - SiRF Customer Support
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gpspassion

93964 Posts

Posted - 31 mars 2005 :  09:58:32  Show Profile  Visit gpspassion's Homepage  Reply with Quote
Yes, but last I checked (version 1.02) SiRFdemoPPC that feature wasn't there unfortunately and I haven't seen it available for public download so far.

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Leif

Sweden
141 Posts

Posted - 06 avr. 2005 :  22:48:24  Show Profile  Reply with Quote
quote:
Originally posted by gpspassion


you can see in the example above that Xtrac v2 doesn't seem to benefit much from SN disabling.



How fast were you moving when doing the test?

The speed treshholds 0.8 to 1.4 m/s mentioned by the FAQ and Carl is in the range 2.9 to 5.0 km/h. You could say slow to fast walking speed. Which treshhold is actually used in the unit you tested or my Yakumo is unknown.

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Carl@SiRF

USA
159 Posts

Posted - 06 avr. 2005 :  23:22:08  Show Profile  Reply with Quote
Your Yakumo software by default has static navigation disabled.

Carl - SiRF Customer Support
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