[Xastir] Re:Xastir and GPS

[J. Lance Cotton]

Curt Mills, WE7U wrote:
> Option 1) Each GPS port should receive lines of data and store them
> in unique storage locations for the type of string, then dump all of
> those strings for processing at the GPS Check Interval.  I do
> remember though that one type of string in a Garmin can be sent
> three times in sequence, and provides info about all satellites that
> are in view.
> 
> Option 2) Really an implementation of Option 1:  Keep a circular
> queue that is large enough to contain all of the unique sorts of
> strings that the GPS can send (GPRMC/GPGGA to the next GPRMC/GPGGA
> string) and dumps that entire queue (about 10 strings or so) for
> processing immediately at the GPS Check Interval.  At other times
> it'll just keep overwriting the circular queue with new data and not
> process the strings.
> 
> Option 3) Dump all GPS data on the ground until the GPS Check
> Interval, at which point Xastir grabs and processes all GPS strings
> received for about two seconds, then the GPS interfaces start
> dumping the data on the ground again.
> 
> Option 4) Close the GPS port when we're not actively wanting data.
> This might interfere with the TNC_AUX operation and interfere with
> sending APRS stations as waypoints to the GPS.  It also can result
> in partial sentences being received during the open/close times.
> 
> I think option 4 is out.  I like option 2.  It seems the most
> appropriate.

I concur; it seems like option 2 most closely emulates what happens with an 
AUX_TNC interface. In a KPC3+ or similar, the aux GPS port writes data whose 
identity string (first few characters) matches what is desired. Each new NMEA 
sentence from the GPS overwrites what was in the LT buffer before it.

We should think about expiring data in the circular queue also. If there is no 
  data coming in from the GPS, the circular queue doesn't get updated, so it 
looks like there is still valid position data which could possible look 'new'.

-Lance

-- 
J. Lance Cotton, KJ5O
http://map.findu.com/kj5o-14
joe at lightningflash.net