MAVLink app: Enable protocol version handshaking

[LorenzMeier]

This allows the ground control station or any other communication partner to query the supported versions. The key aspect is to send the response in MAVLink 2 framing to test the link with a MAVLink 2 framed message.

Before connecting QGC:

instance #0:
	mavlink chan: #0
	no telem status.
	flow control:	OFF
	rates:
	tx: 23.215 kB/s
	txerr: 0.000 kB/s
	rx: 0.000 kB/s
	rate mult: 1.000
	accepting commands: YES
	MAVLink version: 1
	transport protocol: UDP (14556)

After connecting QGC with this extension:

instance #0:
	GCS heartbeat:	988721 us ago
	mavlink chan: #0
	type:		GENERIC LINK OR RADIO
	flow control:	OFF
	rates:
	tx: 30.495 kB/s
	txerr: 0.000 kB/s
	rx: 0.021 kB/s
	rate mult: 1.000
	accepting commands: YES
	MAVLink version: 2
	transport protocol: UDP (14556)

[LorenzMeier]

@mhkabir This hopefully makes your life easier on RTK and @bkueng I hope this makes geofencing easier to work with.

[LorenzMeier]

Output on a Pixhawk:

instance #0:
        GCS heartbeat:  593486 us ago
        mavlink chan: #0
        type:           3DR RADIO
        rssi:           219
        remote rssi:    219
        txbuf:          94
        noise:          61
        remote noise:   58
        rx errors:      0
        fixed:          0
        flow control:   ON
        rates:
        tx: 1.285 kB/s
        txerr: 0.000 kB/s
        rx: 0.021 kB/s
        rate mult: 0.366
        accepting commands: YES
        MAVLink version: 2
        transport protocol: serial (/dev/ttyS1 @57600)

instance #1:
        mavlink chan: #1
        no telem status.
        flow control:   OFF
        rates:
        tx: 0.984 kB/s
        txerr: 0.000 kB/s
        rx: 0.059 kB/s
        rate mult: 0.300
        accepting commands: YES
        MAVLink version: 1
        transport protocol: serial (/dev/ttyS2 @57600)

instance #2:
        GCS heartbeat:  909627 us ago
        mavlink chan: #2
        type:           USB CDC
        flow control:   OFF
        rates:
        tx: 15.062 kB/s
        txerr: 0.000 kB/s
        rx: 0.021 kB/s
        rate mult: 1.000
        accepting commands: YES
        MAVLink version: 2
        transport protocol: serial (/dev/ttyACM0 @2000000)

[LorenzMeier]

@dagar Can you review?

[dagar]

Looks good. I was expecting the handshake to be more involved.
While I was looking around I didn't see mavlink v1.0 actually being used anywhere. Is that correct or did I miss something? Can we drop it?

[LorenzMeier]

The simulator interfaces still depend on v1. They use some hacked serialization which assumes v1 and need to be converted to using the correct library calls.

Searching for "v1.0/"

src/drivers/pwm_out_rc_in/pwm_out_rc_in.cpp:
   52  #include <systemlib/pwm_limit/pwm_limit.h>
   53  #include <dev_fs_lib_serial.h>
   54: #include <v1.0/checksum.h>
   55: #include <v1.0/mavlink_types.h>
   56: #include <v1.0/common/mavlink.h>
   57  
   58  

src/drivers/snapdragon_rc_pwm/snapdragon_rc_pwm.cpp:
   54  #include <uORB/topics/actuator_controls.h>
   55  
   56: #include <v1.0/mavlink_types.h>
   57: #include <v1.0/common/mavlink.h>
   58  
   59  #include "drivers/drv_pwm_output.h"

src/modules/simulator/simulator.h:
   58  #include <uORB/topics/optical_flow.h>
   59  #include <uORB/topics/distance_sensor.h>
   60: #include <v1.0/mavlink_types.h>
   61: #include <v1.0/common/mavlink.h>
   62  #include <geo/geo.h>
   63  namespace simulator

Tools/sitl_gazebo/include/gazebo_mavlink_interface.h:
   45  #include <sdf/sdf.hh>
   46  
   47: #include "mavlink/v1.0/common/mavlink.h"
   48  
   49  #include "gazebo/math/Vector3.hh"