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MavlinkDirect ​

The MavlinkDirect plugin lets you send and receive any MAVLink message, including your own custom ones, by name. The message fields are passed as a JSON string, which makes it a good fit for Python: the json module from the standard library does all the work.

For the concepts, such as the JSON format and how custom XML is loaded, see the C++ guide. The Python API is the same.

Loading a custom message ​

To send or receive a message that is not part of the common.xml dialect, load its XML definition first. In this example we define our own message for a gas sensor:

python
GAS_SENSOR_XML = """
<mavlink>
    <messages>
        <message id="44000" name="GAS_SENSOR">
            <description>Gas concentration measured by a sensor.</description>
            <field type="uint64_t" name="time_usec" units="us">Timestamp (time since system boot).</field>
            <field type="uint8_t" name="id" instance="true">Sensor ID.</field>
            <field type="float" name="co2" units="ppm">CO2 concentration.</field>
            <field type="float" name="ch4" units="ppm">Methane concentration.</field>
            <field type="int16_t" name="temperature" units="cdegC">Sensor temperature.</field>
        </message>
    </messages>
</mavlink>
"""

await mavlink_direct.load_custom_xml(GAS_SENSOR_XML)

Both the sending and the receiving side need to load the same XML.

Sending messages ​

Once loaded, the message can be sent by name, with the fields assembled as a dict and serialized with json.dumps:

python
from mavsdk.asyncio.plugins.mavlink_direct import MavlinkMessage

fields = {
    "time_usec": 1_000_000,
    "id": 0,
    "co2": 420.0,
    "ch4": 1.9,
    "temperature": 2150,
}

message = MavlinkMessage(
    message_name="GAS_SENSOR",
    system_id=configuration.system_id,
    component_id=configuration.component_id,
    target_system_id=0,  # Does not apply for this message
    target_component_id=0,  # Does not apply for this message
    fields_json=json.dumps(fields),
)

await mavlink_direct.send_message(message)

Failures, such as an unknown message name or a field that does not fit, raise a MavlinkDirectError.

Receiving messages ​

On the receiving side, subscribe to the message by name and parse its fields with json.loads:

python
async for message in mavlink_direct.subscribe_message("GAS_SENSOR"):
    fields = json.loads(message.fields_json)
    # The temperature is in cdegC, as given by the message definition.
    print(
        f"GAS_SENSOR {fields['id']} received: "
        f"{fields['co2']:.1f} ppm CO2, {fields['ch4']:.1f} ppm CH4, "
        f"{fields['temperature'] / 100:.1f} degC"
    )

Use an empty string "" as the message name to receive all messages.

Examples ​

The complete examples are available for the asyncio API (sender, receiver) and for the synchronous API (sender, receiver).