Re: [gpsd-dev] Additional SV flags?

[Gary E. Miller]

Yo A.S.!

On Tue, 30 Apr 2019 15:14:02 -0400
"A.S." <address@hidden> wrote:

> Looking into, at least the U-Blox binary protocol, there are some
> additional flags/details set in the UBX-NAV-SVINFO message that aren't
> making it through GPSd.

Once you start looking you will find many things that different GPS
output that gpsd throws away.

> In particular, I'm looking at the "flags" field, of which bits 2 and 3
> would be "nice to have" for the Android HAL, as they correspond
> directly to the HAS_EPHEMERIS_DATA and HAS_ALMANAC_DATA bits of
> GnssSvFlags.
> https://source.android.com/reference/hidl/android/hardware/gnss/1.0/IGnssCallback#gnsssvflags

Why would you care?  If the GPS is outputting good time (2D fix), then
it has the Ephemeris already.  Pretty much one directly follows the other.

> Some location software on Android displays the value of these flags in
> order to give the user an idea about where it is in the process of
> getting a location fix. For example;
> https://github.com/barbeau/gpstest -- displays flags A, E, U for
> Almanac, Ephemeris, and Used.

Since a u-blox 8 goes from cold start to a fix in under about two
minutes, the useful time of that information is short.

The newest GPS, like the u-blox 9, do not even bother to acquire the
Almanac anymore, they go direct to the Ephemeris since they have so many
receive channels.  On the 9 that takes about 6 seconds.

NMEA never bothered to report that data.

The "used" flag for each sat is all over the place.  gpsd just uses the
used flag from the skyview sentences.

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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