SiRF on Emtac/SC BTGPS with TTN2 2.24

Fuego

Now that we should be able to use SiRF mode properly with TTN2 version 2.24, would someone be so kind as to explain the pros/cons of SiRF versus NMEA modes, using a Socketcom/Emtac BTGPS with TTN2 please?

Dave

Oh dear. I experienced this in the beta testing, but it appeared to be fixed in the later betas (didn't notice this anymore on the navigator safety screen). When this happened to me, the pointer would be facing the wrong way if you dropped back to map view and it appeared to then want to jump backwards. Check to see if this happens with you ?

What Pocket PC are you using ? And are you running GPS v2.06 ? If you're running 2.04 then you will exhibit this problem.

RobMob · Regular Visitor Joined: 31/12/2002 09:37:48 Posts: 103

I think I loaded up with Rocket Fuel this morning!! Set TTNAV/Emtac to Sirf mode using SiRF BT driver on GPS Status program at COM 8, after fillig up with Fuel(optimax!). Started driving and WOW - 21,678 MPH (or thereabouts!). My speed now flucuates between 500mph (stationary) to over 21,000 mph. Has anyone experienced this - am I making an obvious mistake somewhere? Chaning back to Emtac wireless driver cures problem - problem asl ooccurs on SiRF 38,400 on COM 8.

RobMob

Dave

Oooh, I think someone's trying to set me a challenge! So let me get this straight, you want 3xPocket PC's, 3xGPS Receivers, a live video camera, and me driving all at the same time ?

Seriously though, I could do an NMEA and SiRF test on a stretch of road, but the chipsets are slightly different, one's running SiRF I and one SiRF IIe, so it might not be a 100% test, but it could be done in a single journey.

Fuego

Well I've done some more driving in SiRF mode and the satellite lock position does transition a lot in patchy areas. Three, or four times a minute, whilst driving down country lanes, with tree cover, isn't unusual.

Does TTN2 react differently to this? I think it does. It seems to do less ad-libbing about your position, which means the "GPS reading not reliable" message appears more, whereas in NMEA mode, it would be trying to guess your position, using last known road speed, along the current route.

Maybe I'm mistaken, but it would be worthwhile driving a short "patchy" route twice, at the same time of day, more or less, in the two different modes, recording a log each time. That is unless you have two identical pieces of kit ;)

The logs could be played back and a quick note could be made of how TTN2 behaves throughout the short route. This assumes that they have fixed the log play-back timing problems, which led to stuttered and slow play-back, previously.

As a control, perhaps a third run could be made with NMEA in 1 second update mode.

Now, how to make a video of the drive with two TTN2 navigator tracks superimposed on it? ;)

Dave

The Emtacs originally exhibited this problem, but was fixed in a firmware update.

MikeB

I believe that this is only a problem with some of the new GlobalSat BT308 receivers. The problem has been fixed in more recent firmware of the GPS but there are about 100 receivers (mine being one) which exhibit this problem.

The Socket/Emtac receivers should be OK. There is no issue with the Fortuna GPSmart as SiRF cannot be set using the BT interface.
_________________
Mike Barrett

Dave

I don't think so. The Emtac Sleeve won't let you use normal utilities like WinFast Navigator, so I think it's probably safe.

The main problem above is more to do with Bluetooth losing connecting to the GPS engine, so I doubt you would see this problem on the sleeve.

johnmar

Dave, does the bug (and the ability to switch modes) also apply to the EMTAC GPS Sleeve?

Thanks
_________________
John

iPAQ3830 (32MB) PPC2002 ROM 1.20
CF Expansion Pack
Holux GR-213 GPS Mouse (GSW3.1.1 -3.1.00.07 C23B1.00)
Kingston Elite Pro 1 GB CF Card for maps
Viking 512MB SD Card (not used for navigating)
TTNav 5.210 (5430) Maps of W Europe

Dave

Yes, you don't really need to use CruxView if you don't want to. Using the specific SiRF driver in TomTom *should* switch it to SiRF at the specific baud rate. TBH I've used WinFast Navigator to switch.

Normally the Emtac BT GPS sits on NMEA 4800. Just be careful when you switch that you don't select say SiRF 57600. If you have a buggy firmware release, it will render your receiver useless until battery and then capacitor has discharged and lost settings. This is a known bug in these receivers, but fixed by the UK Firmware update.

RobMob · Regular Visitor Joined: 31/12/2002 09:37:48 Posts: 103

Would just like to double check something:

To use SiRF do I need to chnage the settings using CruxView and then select the SiRF BT driver in GPS Status program in TTNAV?

Thanks

RobMob

Dave

Fuego, Also a note to beware of, is with the BT GPS's there seems to be issues switching from NMEA to SiRF and switching baud rates at the same time. Although Emtac have provided a firmware patch for this, I'm not sure if it's installed on shipment of the Socket's, or whether the TomTom BT GPS experiences this same problem.

The issue is you can lockup your BT GPS and not recover it again until the battery and backup battery/capacitor has drained completely (3-5 days).

DavidW

Fuego,

I think you did the right thing by just trying it out!

The more frequent updates on the number of satellites is expected. In NMEA mode, typical SiRF based GPSes only send that data every five seconds. In SiRF mode, it is sent every second.

I recall postulating somewhere in the forums as to whether more rapid information about loss of lock and regaining lock (in difficult areas) changes Navigator's behaviour or not - I simply don't know, but I prefer the more rapid updates of this data anyway.

In NMEA mode, it would be possible to configure faster updates of this information if you increase the serial port speed sufficiently - but if you use a TomTom driver for a named SiRF based GPS, you'll find it undoes your reconfiguration (and requires you to have the GPS set at 4800bps).

SiRF mode is arguably a more efficient protocol. Leaving my GPS in SiRF mode also stops me from having to switch my GPS between NMEA and SiRF (for better information from the GPS in Winfast Navigator and for the ability to see 'development' information if I choose to).

You can, if you wish, silence the GPS driver - it's the right hand slider on the second tab of the driver application.

I just have one reservation with SiRF mode as it is currently implemented. As I noted in this thread, the "Reset GPS for this location" feature doesn't work in SiRF mode at present. TomTom have it working with SiRF based GPSes in NMEA mode (if you choose an appropriate driver) - but don't appear to have transported the relevant code into the SiRF drivers. I say "don't appear" simply because I can't make it work on my setup, and it may be an oddity of my setup!

Sometimes my Haicom HI-303MMF GPS is left long enough that the internal battery has gone flat and I need that function for a quick start. However, I can't think it at all necessary for your Bluetooth setup.

Meanwhile, I'm sure others will be interested in your 'real life' experience.

David

Dave

Sorry, missed this one. You will see a faster update rate via SiRF, more beeps is definately one you'll hear, this is something I've been experiencing on my beta testing with TomTom to get this fix rolled out.

Fuego

Well, sadly, no replies to my post.

Still, I tried SiRF mode briefly and this is what I noted:

It definitely does keep the display updated more frequently with the number of satellites in use.

Whether this is just cosmetic, or whether this stops the TTN2 software from trying to unnecessarily second-guess the position, is questionable.

This does have the side-effect that you will get more beeps and buzzes, as you drive along, and the sat count drops to zero for a second, or two. That's probably not a good thing in patchy areas.

Overall I had the impression that TTN2 was keeping better track, in SiRF mode, but this is just a subjective opinion, at this stage.

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