[Xastir] NMEA v2.1 GSA Sentences case very high CPU load

[Chris Bell]

> On Wed, 5 Mar 2003, Jeff Laughlin wrote:
> 
> > When the GPS unit is in v2.1 mode, XASTIR and X cause very high CPU loads.
> 
> > I believe the cause of this load is that every second XASTIR prints in the
> > status line "Got GGA String" then "Got RMC String". It probably shouldn't
> > print those status strings.
> >
> > So, why not just use the v1.5 modes? There are two good reasons.
> > 1: The v1.5 modes do not output altitude.
> > 2: My TH-D7a requires v2.1
> >
> > So there you have it. The solution is probably as simple as just not
> > printing those status strings every time it gets those sentences.
> 
> Sounds reasonable as a fix.  The problem then comes in:  How to let
> people know that valid data is being seen?  Perhaps just let them
> know when a GPS interface is enabled and valid data is NOT being
> seen?
> 
> What do people think about this one?
> 
> Because of that last problem Jeff brought up (a very good one Jeff,
> made me have to _think_!), I'm wanting to do a popup when GPS data
> goes stale anyway, letting the user know that posits are disabled
> and that the GPS needs to be checked.
> 

I agree we need some status on gps data (what cable just fell out the
back?).  I have been looking at this gps-cpu issue as well.  My first
guess at a fix was to limit the gps data to the gps-check-interval.
It looks like it only checks gps data on the interval, but with a
dedicated interface (like serial, or gpsd) all the other strings get
processed at once.  We should flush out the old data, then just
process one set and go on with life.  My normal setup uses the second
port off the kpc3+ to get gps data, so it is polled, and only gets one
set, which works great.  CPU usage is very low.  When I switched to
gpsd for a bit, it would queue up ALL the data collected in the
interval, and try to process it all at once.  Each datapoint created
more trackpoints, screen updates, and screen status messages.  My P3
1Ghz laptop could not keep up.  

Just something else to look into... :)  

Chris.