xxGNS parsing issue about nmea

[elpiel]

Hello @StefanB7,
I've missed posting my comment in September to the issue so sorry about the delay.
First of all - thank you for reporting the issue!

Do you have any specific questions? Maybe you can take a look at nom first and see how we can parse more than the 2 we have defined now.

Accordingly to the gpsd docs - https://gpsd.gitlab.io/gpsd/NMEA.html#_gns_fix_data, the first two are for GPS and GLONASS.
We could read all characters up to the comma , with nom, parse the first one (GPS) and the rest we could put behind an Option.
We could keep the 2nd FAA mode required then and have a heapless::Vec (fixed size Vec) with maximum of e.g. 4 (6 total - 2).

struct FaaModes {
   /// This is usually GPS
   sys_state0: FaaMode,
   //// Rest of the fix flags, could be 0 or more than 1
   sys_staten: Option<FaaModesN>,
}

struct FaaModesN {
    /// Usually GLONASS
    sys_state1: FaaMode,
    sys_states: heapless::Vec<FaaMode, 4>,
}

Do you know if u-blox defines a maximum number of FAA modes that it can return?
Maybe there's something in the Datasheet for your module?