[hafqa] [hafqa] [Bug 2878] Very poor satellite acquisition with internal GPS

[From: bugzilla-daemon at maemo.org]

https://bugs.maemo.org/show_bug.cgi?id=2878





------- Comment #32 from maemo at subs.maneos.org  2008-07-12 13:16 GMT+3 -------
(In reply to comment #22)
> So far this has been fixable by killing the stuck supld and restarting the GPS
> application.

But not today :-(

Killed stuck supld, started maemo mapper, got "0/11" satellites almost
immediately, but it took about 10' to get a fix.

Repeated several times over the last few hours.  Lowest TTF was around 2',
whereas yesterday it could do it in under 30".  Things that didn't make a
difference:
- rebooting the N810
- uninstalling & reinstalling agps-ui
- removing /var/lib/gps/{gps_last_saved_report,nvd_data} (but they do get
recreated after the next session)

The location shown in agps-ui was correct during that time.

I also did some observation of maemo mapper's "GPS details" view.  After a fix
is obtained the satellite positions shift significantly (certainly more than
justified by the few minutes interval).  Cycling the GPS puts them back to
their pre-fix positions.  I can attach screenshots demonstrating this if
needed.

This suggests that the ephemeris data is not preserved (although the almanac
is) and/or we are getting fed bogus data from supl.nokia.com. I have no idea
whether this is the expected mode of operation or why it was working fine for
me in the past few days.

Speaking of which, I was monitoring traffic from the N810 (using tcpdump on the
router) and it seems that supld only tries to get new data once every 30'. 
This seems reasonable since ephemeris data is only supposed to be valid for
that length of time, but if it's incorrect and/or not cached we're still
effectively doing a cold start every time.

It would be useful to know which of the almanac / ephemeris are retrieved from
supl.nokia.com, which of the two are cached, and whether the cache stores the
data retrieved from the SUPL server or from the GPS chip.

(In reply to comment #11)
> Would it be fair to say that this bug report is now fixed by the A-GPS
> functionality, and then study the exceptions as new bugs, getting all the
> details to replicate etc?

Well, part of the problem is that A-GPS is currently advertised as beta and is
mostly undocumented.  Some release notes describing its operation, known issues
etc wouldn't hurt.  It would also be nice to have a more specific bugzilla
component for this.


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