[Ovmsdev] How to get a quick and reliable GPS fix

[Arthur Hebert]

Thanks for the info Christopher and Michael! I'll try it without resetting,
and see if that helps.

-Arthur

On Wed, Nov 5, 2014 at 4:20 AM, Michael Balzer <dexter at expeedo.de> wrote:

>  Hi Arthur,
>
> the SIM908 hardware design doc says:
>
> *Power down mode: The GPS engine will be set into this mode by sending AT
> command “AT+CGPSPWR=0”. In this mode the internal power supply for GPS will
> be shutdown, and the current consumption is very low. The last position,
> current time and ephemeris data will be stored in the GSM host memory.*
>
> ...and...
>
> *User can power on GPS engine by sending AT command “AT+CGPSPWR=1”. *
>
> So it seems a GPS reset is not necessary after a software power down /
> sleep state, I'd first try without.
>
> If you find out you need to do a reset, I'd first try to cope with "hot" /
> "warm". The command manual says:
>
> *COLD start mode is recommended For first time reset.*
>
> So I think this is normally only needed for the first power up.
>
> Regards,
> Michael
>
>
>
> Am 04.11.2014 um 17:42 schrieb Arthur Hebert:
>
> Hi All,
>
>  Does anyone know the details of how, most reliably and most quickly, to
> get a location fix from the GPS module after it has been powered up and
> after it has come out of sleep mode?
>
>  I have written my own code using the OVMS hardware. To save power, it
> turns off the GPS power (AT+CGPSPWR=0) and puts the module to sleep
> (AT+CSCLK=2) while the vehicle is parked (i.e. no CAN bus activity). Once
> there is CAN activity again, it comes out of sleep mode (AT+CSCLK=0) and
> turns on the GPS (AT+CGSPPWR=1). Immediately after turning on the GPS
> power, I also issue one of the GPS reset commands (AT+CGPSRS=0 or
> AT+CGPSRST=1).
>
>  The module documentation if vague about when to use the 0 reset or the 1
> reset.
>
>  I know that the GPS module itself isn't made to function while the
> module is asleep even though the commands may not give an error.
>
>  I've read that it takes up to 15 minutes to get a fix on most GPS
> devices. In practice, sometimes I get a fix within a minute every time I
> start up, and other times I don't get a fix even after hours of trying with
> either reset option.
>
>  Any information will be greatly appreciated.
>
>  Thanks,
> Arthur
>
>
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>
>
> --
> Michael Balzer * Paradestr. 8 * D-42107 Wuppertal
> Fon 0202 / 272 2201 * Handy 0176 / 206 989 26
>
>
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