Re: [gpsd-dev] ✘GPSD_API

[Gary E. Miller]

Yo Hal!

On Wed, 13 Apr 2016 14:15:59 -0700
Hal Murray <address@hidden> wrote:

> address@hidden said:
> > I'm thinking satellites_visible_cnt and satellites_used_cnt can get
> > biried in nmea_t and nt affect the API.   
> 
> There is nothing NMEA specific about satellites used or visible.

Yes, there is.

Many GPS report sats used and sats visible as integers in an NMEA xxGGA
message or device specific message.

Many GPS report sats used incrementally in NMEA xxGSA and xxGSV
messages.  So the sats used and visible are used as conters between
messages until the final count is reached.

Some GPS do both, and often the integer and counter values do not match!

Worse yet, the counter may be overwritten by the interger, leading to
running off the end of an array.  I have recently seen this.

It is possible some other drivers have the problem but a simple grep
did not find me any.

> That may be the right place for them, but it without checking more it
> looks a bit strange.

The counters are more internal variables, and only used in the NMEA, and
(I think) the TSIP drivers.  So probably they do not need to be visible
outside the NMEA drivver or in the ABI.  Somewhere in the cycle if
the integer values are not set there may be a reason to copy the completed
counters into the integers.

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

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