examples: add two MavlinkDirect examples

This is to demonstrate the new MavlinkDirect functionality.

Author: julianoes

examples/mavlink_direct_receive.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python3
+
+import asyncio
+from mavsdk import System
+import json
+
+
+async def print_messages():
+    drone = System()
+    print("Waiting for drone to connect...")
+    await drone.connect(system_address="udpin://0.0.0.0:14540")
+
+    async for state in drone.core.connection_state():
+        if state.is_connected:
+            print(f"-- Connected to drone!")
+            break
+
+    async for message in drone.mavlink_direct.message("ATTITUDE"):
+        fields = json.loads(message.fields_json)
+
+        # Format as JSON again for the reader but this time with indenting.
+        fields_formatted = json.dumps(fields, indent=4)
+
+        print(f"{message.message_name} from {message.system_id}/{message.component_id}:")
+        print("----")
+        print(f"{fields_formatted}")
+        print("----")
+
+
+if __name__ == "__main__":
+    asyncio.run(print_messages())

examples/mavlink_direct_send.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+
+import asyncio
+from mavsdk import System, mavlink_direct
+import json
+import random
+
+
+async def send_airspeed():
+    drone = System()
+    print("Waiting for drone to connect...")
+    await drone.connect(system_address="udpin://0.0.0.0:14540")
+
+    async for state in drone.core.connection_state():
+        if state.is_connected:
+            print(f"-- Connected to drone!")
+            break
+
+    await drone.mavlink_direct.load_custom_xml("""
+    <mavlink>
+      <messages>
+        <message id="295" name="AIRSPEED">
+          <description>Airspeed information from a sensor.</description>
+          <field type="uint8_t" name="id" instance="true">Sensor ID.</field>
+          <field type="float" name="airspeed" units="m/s">Calibrated airspeed (CAS).</field>
+          <field type="int16_t" name="temperature" units="cdegC">Temperature. INT16_MAX for value unknown/not supplied.</field>
+          <field type="float" name="raw_press" units="hPa">Raw differential pressure. NaN for value unknown/not supplied.</field>
+          <field type="uint8_t" name="flags" enum="AIRSPEED_SENSOR_FLAGS">Airspeed sensor flags.</field>
+        </message>
+      </messages>
+    </mavlink>
+    """)
+
+    for i in range(20):
+        print(f"Sending airspeed {i}...")
+        fields = {
+            "id": 0,
+            "airspeed": random.random() * 10,
+            "temperature": 20 * 100,
+            "raw_press": 1010,
+            "flags": 0,
+        }
+
+        message = mavlink_direct.MavlinkMessage(
+            message_name="AIRSPEED",
+            system_id=245,
+            component_id=25,
+            target_system_id=0,
+            target_component_id=0,
+            fields_json=json.dumps(fields),
+        )
+        await drone.mavlink_direct.send_message(message)
+        await asyncio.sleep(0.1)
+
+
+if __name__ == "__main__":
+    asyncio.run(send_airspeed())