GPSCAT vs. GPSD vs. LIBGPS (LIBGPSMM) (Problems)

I am using GPSD 2.3.4. I am on a Ubuntu6.10  laptop and using an ATEN RS232 to USB cabel to talk to my Gamin GPS 17 receiver.

Problem 1
-------------

With GPSCAT I can run it as follows and it produces a lovely flow for NMEA sentences from my Garmin GPS 17.

gpscat -s4800N1 /dev/ttyUSB0

So all good so far.

But, wiith GPSD I run it as follows:

gpsd -N -n -D 2 /dev/ttyUSB0

but it keeps producing the line :

...unknown sentence: "$PGRMM, WGS 84*06\x0d\x0a" and none of the nice stuff that GPSCat produces. So, why is GPSCAT working fine and not GPSD? Or is this correct operation??


Problem 2
--------------

Ok so this is the main issue as I want to write an application in C++. In my app I am using lbgpsmm/libgps. There I do an open("localhost", "/dev/ttyUSB0") ... but it just keeps returning "Error opening gpsd". So, what can possibly be wrong there?


Problem 3
------------

I tried to use the set_callback function but that just hangs and seems to do nothing. I dont get past that line in the code. Any ideas?


Thanks in advance for your help.

Mark