Add and use AP_NMEA_Input

[peterbarker]

This factors out the NMEA parsing code from AP_Windvane_NMEA, in an attempt to reduce the number of NMEA parsers we have in our code.

Anything that wants to parse NMEA inherits from AP_NMEA_Input (multiple inheritance, typically, yech, but...) and implements these methods:

    // called when we're just about to start parsing a sentence:
    virtual void reset_at_sentence_begin() = 0;

    // called when the sentence type has been determined; should
    // return true if this sentence should be fully decoded
    virtual bool start_sentence_type(const char *term_type) = 0;

    // called as every term is decoded in a handled sentence.
    // Sentence may yet be invalid - handle_decode_success will be
    // called if the term should *actually* be used.  Should return
    // false if the value in this term makes the sentence invalid.
    virtual bool handle_term(uint8_t term_number, const char *term) = 0;

    // called when a complete sentence has been decoded and passed checksum:
    virtual void handle_decode_success() = 0;

Tested only as far as "it compiles" (and whatever is in autotest, now :-) )

@IamPete1

[peterbarker]

I should note that if we didn't want to do the multiple-inheritance thing then we could do something like

parser = new NMEAParser(protocol, protocol_instance, functor_reset, functor_good_sentence_type, functor_term, functor_decode_complete);

Pete Hall also tried this here: #12289

[rmackay9]

By the way, I'm planning to add consumption of temperature to the rangefinder library's NMEA driver which is normally used for depth sounders. A number of users have asked to be able to retrieve and log the water temperature.

If you wanted me to try and modify the RangeFinder library to try and use this I perhaps could.

[IamPete1]

@rmackay9 We can already read the MTW temp sentence via the airspeed lib (#14852). The hack is just to connect two serial port rx pins to the NMEA tx. Does require taking up two serial ports tho, but there is not really any other way to get round it for sensors that can do depth and temp and water speed, unless we add virtual serial ports or something complicated.

[rmackay9]

@IamPete1,

I was going to basically duplicate that consumption of the MTW sentence in the AP_RangeFinder_NMEA driver.. and then make it accessible with a method that returns a bool on success. It would only ever be called when we go to log the DPTH message.

[peterbarker]

@rmackay9 sounds good - I'll probably try to convert AP_GPS_NMEA - happen to have a GPS that produces that on my desk ATM.

[Ryanf55]

Nice, seems like a lot less code duplication. Were you able to run the size compare?