Power Save/trickle

[Peter Kessler]

Two questions:



1) Can anyone tell me what exactly happens in trickle/power save mode? What do you gain and what do you lose?



2) Are the models of the BT308 now available cured of the early firmware problems, and where can one get the latest firmware?



many thanks
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Peter Kessler

[DavidW]

Trickle mode may well not apply to the Bluetooth GPSes - I just don't know. It's a GPS chipset feature which keeps the chipset powered down for some of the time.



The advantage is that you save power. The disadvantage is that lose features - on a SiRF II chipset, you can't have SBAS (WAAS / EGNOS) if you have any trickle mode engaged, and if you enable the more aggressive trickle modes, you save more power but get a fix less than once a second.





No idea on the other question - sorry.







David

[Peter Kessler]

Thanks, David
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Peter Kessler

[MikeB]

Peter,



As far as I know the BT308 can use trickle power. Basically the unit goes into standby for a period, then wakes up for 300 milliseconds processes the signals received, transmits a status message then goes back to stanby mode again.



David,

Are you sure you lose SBAS functionality in trickle mode?



I dont see an issue with getting a fix once a second as that is all that NMEA outputs anyway, and also unless you are in a jet plane or travelling very fast the update rate doesn't really matter too much, surely.



For instance when walking you could probably take a reading every 10 seconds or more and be accurate enough to navigate by. If you are travelling in a jet at Mach 1 then you only reallly need to know with say 10 miles where you are 5 metre accuracy is somewhat meaningless. As you slow down the accuracy would become more important. Therefore the update rate is useful only in proportion to the speed you are travelling, the faster you are travelling, the less frequent update (or more warning time raquired).



Just a thought. I have always wondered why when hurtling along a motorway at 70(ish) having your position updated less than 1 or 2 seconds is important. The next junction 20 miles down the road is about 1027 updates away what is the difference between 500, 1000, and 2000 or 2seconds, 1 second or 1/2 second?



As for suppliers of the BT3008 checkout the review and contact the UK distributer, he should be able to point you to your nearest dealer.
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Mike Barrett

[DavidW]

Mike,



Unfortunately, I can't now verify that SBAS is disabled in trickle power mode. I was sure I had seen this documented as a restriction somewhere, but I can't verify it from the SiRF documentation I have, and I can't easily test this either.





I can run SiRFdemo 3.40 with my SiRFstar IIe/LP based HI-303MMF, but I really have to use CompactFlash to do that, otherwise I have no serial input to the GPS and I can't therefore configure it.



Unfortunately, the laptop puts out so much RF noise that GPS reception with the GPS in a PC Card slot is too poor for SBAS reception. I don't have an external antenna for the GPS to overcome the noise. I really do need to sort out a better testbed!





My understanding was that trickle power mode shut down the signal processing part of the SiRF chipset. That was why I think it was believed to be incompatible with SBAS - you can't be decoding the SBAS data stream if the signal processing circuitry is shut down.







David



(feeling a bit shaky about these conclusions, because he can neither back them with documentation nor experimental results)

[MikeB]

David,



You may well be right, it is just that I had never seen this documented anywhere. My own conclusions are far more likely to be faulty. It just seemed to me that if the unit is powered up it should be able to process all signals received, including those from the SBAS satelitte.



I havent seen a differential fix for quite a while now so my testing would not be conclusive. When I have a little time I will see if I can prove this one way or another.
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Mike Barrett

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