[maemo-users] N810 gps troubles

From: Frederic Crozat fred at crozat.net
Date: Mon Mar 31 21:44:58 EEST 2008
On Mon, Mar 31, 2008 at 7:45 PM, Andrew Daviel <advax at triumf.ca> wrote:
> On Mon, 31 Mar 2008, Frederic Crozat wrote:
>  > Once you get the almanac downloaded, fix time can be shorter (5
>  > minutes to 10 minutes in bad conditions). And if you got a fix in the
>  Any idea where the almanac is stored ? In the GPS chip itself ? Does it
>  survive power-down or dead battery ? I gather it's a Texas device
>  (GPS5300) with not a lot of info on the Web (contact TI if you're a
>  cellphone maker wanting millions of the things, hobbyists need not
>  apply). The 2-page teaser suggests that it communicates over a serial
>  bus, maybe native NMEA0183.

There has been a lot of discussions on Internet Tablet forum. It is
probably stored in /var/lib/gps/nvd_data but nobody has been able to
decode the file format.

>  > Also remember GPS antenna is located under the zoom in/out button, so
>  > try to not hold your n810 with your hand over them (at least for
>  > initial GPS fix).
>  I had assumed it was the little plastic square just above the camera, so
>  that the best orientation was screen side upwards with a good view of the
>  sky. Once I had a fix, then I could put it in my pocket riding a bike.

No, the plastic square is the light sensor ;)

But I concur with your findings about keeping a fix once you get it.

>  I'm not sure Maemo Mapper really has more information available.
>  As far as I can figure, gpsd translates NMEA from the device to a
>  generic format and makes it available to multiple clients on
>  localhost:2947.
>  The NMEA includes $GPGSV GPS Satellites in View. You can see this if you
>  connect to the socket with netcat and give an "r" (raw) command, or
>  "q" or "y".
>  In Nokia Map the "gps view" shows signal levels and satellite position
>  graphically, I presume derived from this information.

Yes, but accessing those "detailed" informations from Maps is
preventing use of the application, unlike Maemo-Mapper (you can even
bind "show GPS details" to a hardware key). And even Maemo-Mapper
"establishing GPS fix" progress bar is a good indicator for fix

>   - I'm curious. What time-to-first-fix are people experiencing ?

Between 5 to 10 minutes usually (in Paris). After a fix, I've done
more tests in disabling GPS and enabling it back and was sometime able
to get fix from 30s to 2 minutes (inside a bus moving..)

>  (I guess I should quantify my own experience..)

Install gps-clockd, it record TTF, as well as syncing clock to GPS clock

Frederic Crozat

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