I wrote a high performance gpsd for the KR1 router at evdoforums.com (search the kr1 support forum for GPSD).

It generates KML files, one every 5 minutes plus a live version that you can update every few seconds, a Google maps mashup, etc.

The GPLv3 Source is at:

http://homepage.mac.com/tz1/.Public/KR1Stuff/minigpsd.c

Though I think I have a few updates. Buried in the KML as XML comments is the J1850 datastream from my motorcycle including gear, RPM, etc. but you might not use that feature.

Anyway, it takes NMEA from /dev/ttyS1 and does all the decoding (integer math for speed). You might want to look at the source for ideas. I'm adapting it and my zmapper - I have it now automatically starting up the GPS, but I need to tweak QT for shutting down properly.