8A groups are defined as ODA (Open Data Application) and are assigned to TMC when specific flag is sent in group 3A (from EN50067:1998 for Europe or RBDS standard for US). In my screenshot you can see the presence of 8A and relative TMC messages in natural language (Italian).
Coming back to GPS/TMC I'm able to emulate it (the GNS 1.0 protocol is very simple, but I have no infos on 2.0). What I need is to create a virtual com port: let's see some more on MS DDK.
The GNS protocol is nothing more that RDS groups mixed with GPS messages. By a serial port log and some reverse engineering:
$GPGGA,104137?¢Jc 3?.149,0000.0000,N,00000.0000,E,0,00,50.?¢åEœL¤? 0,0.0,M,,,,0000*37
As you can see, there're two blocks of data mixed in the GPS message. Both are 10 bytes long and in this form:
?<B1><B2><B3><B4>?
Bn is 2 bytes = a block data
B1..B4 is a RDS group
Very simple!!
From the Terratec API you posted seems that the API exposes only high level data so no access to raw groups
This night I'm going to do some refactoring on my code to enable also group plugins so it can decode from GPS/TMC also
