mirror of
https://github.com/PX4/PX4-Autopilot.git
synced 2025-12-07 18:59:29 +08:00
Docs: add skeleton topic for indicating protocol support
This commit is contained in:
Hamish Willee
@@ -722,12 +722,13 @@
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- [AirspeedValidatedV0](msg_docs/AirspeedValidatedV0.md)
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- [VehicleAttitudeSetpointV0](msg_docs/VehicleAttitudeSetpointV0.md)
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- [VehicleStatusV0](msg_docs/VehicleStatusV0.md)
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- [MAVLink Messaging](middleware/mavlink.md)
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- [MAVLink Messaging](mavlink/index.md)
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- [Adding Messages](mavlink/adding_messages.md)
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- [Streaming Messages](mavlink/streaming_messages.md)
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- [Receiving Messages](mavlink/receiving_messages.md)
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- [Custom MAVLink Messages](mavlink/custom_messages.md)
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- [Standard Modes Protocol](mavlink/standard_modes.md)
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- [Protocols/Microservices](mavlink/protocols.md)
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- [Standard Modes Protocol](mavlink/standard_modes.md)
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- [uXRCE-DDS (PX4-ROS 2/DDS Bridge)](middleware/uxrce_dds.md)
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- [Modules & Commands](modules/modules_main.md)
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- [Autotune](modules/modules_autotune.md)
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88
docs/en/mavlink/index.md
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88
docs/en/mavlink/index.md
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@@ -0,0 +1,88 @@
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# MAVLink Messaging
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[MAVLink](https://mavlink.io/en/) is a very lightweight messaging protocol that has been designed for the drone ecosystem.
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PX4 uses _MAVLink_ to communicate with ground stations and MAVLink SDKs, such as _QGroundControl_ and [MAVSDK](https://mavsdk.mavlink.io/), and as the integration mechanism for connecting to drone components outside of the flight controller: companion computers, MAVLink enabled cameras, and so on.
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This topic provides a brief overview of fundamental MAVLink concepts, such as messages, commands, and microservices.
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It also links instructions for how you can add PX4 support for:
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- [Adding Standard Messages](../mavlink/adding_messages.md)
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- [Streaming MAVLink messages](../mavlink/streaming_messages.md)
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- [Handling incoming MAVLink messages (and writing to a uORB topic)](../mavlink/receiving_messages.md)
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- [Custom MAVLink Messages](../mavlink/custom_messages.md)
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- [Protocols/Microservices](../mavlink/protocols.md)
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::: info
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We do not yet cover _command_ handling and sending, or how to implement your own microservices.
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:::
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## MAVLink Overview
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MAVLink is a lightweight protocol that was designed for efficiently sending messages over unreliable low-bandwidth radio links.
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_Messages_ are simplest and most "fundamental" definition in MAVLink, consisting of a name (e.g. [ATTITUDE](https://mavlink.io/en/messages/common.html#ATTITUDE)), id, and fields containing relevant data.
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They are deliberately lightweight, with a constrained size, and no semantics for resending and acknowledgement.
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Stand-alone messages are commonly used for streaming telemetry or status information, and for sending commands where no acknowledgement is required - such as setpoint commands sent at high rate.
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The [Command Protocol](https://mavlink.io/en/services/command.html) is a higher level protocol for sending commands that may need acknowledgement.
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Specific commands are defined as values of the [MAV_CMD](https://mavlink.io/en/messages/common.html#mav_commands) enumeration, such as the takeoff command [MAV_CMD_NAV_TAKEOFF](https://mavlink.io/en/messages/common.html#MAV_CMD_NAV_TAKEOFF), and include up to 7 numeric "param" values.
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The protocol sends a command by packaging the parameter values in a `COMMAND_INT` or `COMMAND_LONG` message, and waits for an acknowledgement with a result in a `COMMAND_ACK`.
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The command is resent automatically if no acknowledgment is received.
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Note that [MAV_CMD](https://mavlink.io/en/messages/common.html#mav_commands) definitions are also used to define mission actions, and that not all definitions are supported for use in commands/missions on PX4.
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[Microservices](https://mavlink.io/en/services/) are other higher level protocols built on top of MAVLink messages.
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They are used to communicate information that cannot be sent in a single message, and to deliver features such as reliable communication.
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The command protocol described above is one such service.
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Others include the [File Transfer Protocol](https://mavlink.io/en/services/ftp.html), [Camera Protocol](https://mavlink.io/en/services/camera.html) and [Mission Protocol](https://mavlink.io/en/services/mission.html).
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MAVLink messages, commands and enumerations are defined in [XML definition files](https://mavlink.io/en/guide/define_xml_element.html).
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The MAVLink toolchain includes code generators that create programming-language-specific libraries from these definitions for sending and receiving messages.
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Note that most generated libraries do not create code to implement microservices.
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The MAVLink project standardizes a number of messages, commands, enumerations, and microservices, for exchanging data using the following definition files (note that higher level files _include_ the definitions of the files below them):
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- [development.xml](https://mavlink.io/en/messages/development.html) — Definitions that are proposed to be part of the standard.
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The definitions move to `common.xml` if accepted following testing.
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- [common.xml](https://mavlink.io/en/messages/common.html) — A "library" of definitions meeting many common UAV use cases.
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These are supported by many flight stacks, ground stations, and MAVLink peripherals.
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Flight stacks that use these definitions are more likely to interoperate.
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- [standard.xml](https://mavlink.io/en/messages/standard.html) — Definitions that are actually standard.
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They are present on the vast majority of flight stacks and implemented in the same way.
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- [minimal.xml](https://mavlink.io/en/messages/minimal.html) — Definitions required by a minimal MAVLink implementation.
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The project also hosts [dialect XML definitions](https://mavlink.io/en/messages/#dialects), which contain MAVLink definitions that are specific to a flight stack or other stakeholder.
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The protocol relies on each end of the communication having a shared definition of what messages are being sent.
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What this means is that in order to communicate both ends of the communication must use libraries generated from the same XML definition.
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<!--
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The messages are sent over-the-wire in the "payload" of a [MAVLink packet](https://mavlink.io/en/guide/serialization.html#mavlink2_packet_format).
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In order to reduce the amount of information that must be sent, the packet does not include the message metadata, such as what fields are in the message and so on.
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Instead, the fields are serialized in a predefined order based on data size and XML definition order, and MAVLink relies on each end of the communication having a shared definition of what messages are being sent.
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The shared identity of the message is conveyed by the message id, along with a CRC ("`CRC_EXTRA`") that uniquely identifies the message based on its name and id, and the field names and types.
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The receiving end of the communication will discard any packet for which the message id and the `CRC_EXTRA` do not match.
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-->
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## PX4 and MAVLink
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PX4 releases build `common.xml` MAVLink definitions by default, for the greatest compatibility with MAVLink ground stations, libraries, and external components such as MAVLink cameras.
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In the `main` branch, these are included from `development.xml` on SITL, and `common.xml` for other boards.
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::: info
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To be part of a PX4 release, any MAVLink definitions that you use must be in `common.xml` (or included files such as `standard.xml` and `minimal.xml`).
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During development you can use definitions in `development.xml`.
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You will need to work with the [MAVLink team](https://mavlink.io/en/contributing/contributing.html) to define and contribute these definitions.
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:::
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PX4 includes the [mavlink/mavlink](https://github.com/mavlink/mavlink) repo as a submodule under [/src/modules/mavlink](https://github.com/PX4/PX4-Autopilot/tree/main/src/modules/mavlink).
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This contains XML definition files in [/mavlink/messages/1.0/](https://github.com/mavlink/mavlink/blob/master/message_definitions/v1.0/).
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The build toolchain generates the MAVLink 2 C header files at build time.
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The XML file for which headers files are generated may be defined in the [PX4 kconfig board configuration](../hardware/porting_guide_config.md#px4-board-configuration-kconfig) on a per-board basis, using the variable `CONFIG_MAVLINK_DIALECT`:
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- For SITL `CONFIG_MAVLINK_DIALECT` is set to `development` in [boards/px4/sitl/default.px4board](https://github.com/PX4/PX4-Autopilot/blob/main/boards/px4/sitl/default.px4board#L36).
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You can change this to any other definition file, but the file must include `common.xml`.
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- For other boards `CONFIG_MAVLINK_DIALECT` is not set by default, and PX4 builds the definitions in `common.xml` (these are build into the [mavlink module](../modules/modules_communication.md#mavlink) by default — search for `menuconfig MAVLINK_DIALECT` in [src/modules/mavlink/Kconfig](https://github.com/PX4/PX4-Autopilot/blob/main/src/modules/mavlink/Kconfig#L10)).
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The files are generated into the build directory: `/build/<build target>/mavlink/`.
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53
docs/en/mavlink/protocols.md
Normal file
53
docs/en/mavlink/protocols.md
Normal file
@@ -0,0 +1,53 @@
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# MAVLink Microservices (Protocols)
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MAVLink "microservices" are a protocols that use multiple messages exchanged between components to communicate more complicated information.
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For example, the [Command Protocol](https://mavlink.io/en/services/command.html) provides an efficient mechanism for packaging a command in a (particular) message and receiving acknowledgement of the command in another message.
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MAVLink microservices are documented the [MAVLink Guide](https://mavlink.io/en/services/) (this is not exhaustive: not all messages are grouped into protocols and not all protocols are documented).
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This section lists the services known to be supported/not supported by PX4 in this version.
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## Supported Microservices
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These services are known to be supported in some form:
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- [Battery Protocol](https://mavlink.io/en/services/battery.html)
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- [BATTERY_STATUS](https://mavlink.io/en/messages/common.html#BATTERY_STATUS) and [BATTERY_INFO](https://mavlink.io/en/messages/common.html#BATTERY_STATUS) are streamed.
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- Camera Protocols
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- [Camera Protocol v2](https://mavlink.io/en/services/camera.html)
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- [Camera Definition](https://mavlink.io/en/services/camera_def.html)
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- [Camera Protocol v1 (Simple Trigger Protocol)](https://mavlink.io/en/services/camera_v1.html)
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- [Command Protocol](https://mavlink.io/en/services/command.html)
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- [Component Metadata Protocol (WIP)](https://mavlink.io/en/services/component_information.html)
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- [Events Interface (WIP)](https://mavlink.io/en/services/events.html)
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- [File Transfer Protocol (FTP)](https://mavlink.io/en/services/ftp.html)
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- Gimbal Protocols
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- [Gimbal Protocol v2](https://mavlink.io/en/services/gimbal_v2.html)
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- Can be enabled by [Gimbal Configuration](../advanced/gimbal_control.md#mavlink-gimbal-mnt-mode-out-mavlink)
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- PX4 an act as a MAVLink Gimbal for one FC-connected Gimbal
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- [Gimbal Protocol v1 (superseded)](https://mavlink.io/en/services/gimbal.html)
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- [Heartbeat/Connection Protocol](https://mavlink.io/en/services/heartbeat.html)
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- [High Latency Protocol](https://mavlink.io/en/services/high_latency.html) — PX4 streams [HIGH_LATENCY2](https://mavlink.io/en/messages/common.html#HIGH_LATENCY2)
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- [Image Transmission Protocol](https://mavlink.io/en/services/image_transmission.html)
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- [Landing Target Protocol](https://mavlink.io/en/services/landing_target.html)
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- [Manual Control (Joystick) Protocol](https://mavlink.io/en/services/manual_control.html)
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- [MAVLink Id Assignment (sysid, compid)](https://mavlink.io/en/services/mavlink_id_assignment.html)
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- [Mission Protocol](https://mavlink.io/en/services/mission.html)
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- [Offboard Control Protocol](https://mavlink.io/en/services/offboard_control.html)
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- [Remote ID](../peripherals/remote_id.md) ([Open Drone ID Protocol](https://mavlink.io/en/services/opendroneid.html))
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- [Parameter Protocol](https://mavlink.io/en/services/parameter.html)
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- [Parameter Protocol Extended](https://mavlink.io/en/services/parameter_ext.html) — Allows setting string parameters. Used for setting string parameters set in camera definition files.
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- [Payload Protocol](https://mavlink.io/en/services/payload.html)
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- [Ping Protocol](https://mavlink.io/en/services/ping.html)
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- [Standard Modes Protocol](mavlink/standard_modes.md)
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- [Terrain Protocol](https://mavlink.io/en/services/terrain.html)
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- [Time Synchronization](https://mavlink.io/en/services/timesync.html)
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- [Traffic Management (UTM/ADS-B)](https://mavlink.io/en/services/traffic_management.html)
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- [Arm Authorization Protocol](https://mavlink.io/en/services/arm_authorization.html)
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## Unsupported
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These services are not supported/used by PX4:
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- [Illuminator Protocol](https://mavlink.io/en/services/illuminator.html)
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- [Tunnel Protocol](https://mavlink.io/en/services/tunnel.html)
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@@ -1,87 +1 @@
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# MAVLink Messaging
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[MAVLink](https://mavlink.io/en/) is a very lightweight messaging protocol that has been designed for the drone ecosystem.
|
||||
|
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PX4 uses _MAVLink_ to communicate with ground stations and MAVLink SDKs, such as _QGroundControl_ and [MAVSDK](https://mavsdk.mavlink.io/), and as the integration mechanism for connecting to drone components outside of the flight controller: companion computers, MAVLink enabled cameras, and so on.
|
||||
|
||||
This topic provides a brief overview of fundamental MAVLink concepts, such as messages, commands, and microservices.
|
||||
It also links instructions for how you can add PX4 support for:
|
||||
|
||||
- [Adding Standard Messages](../mavlink/adding_messages.md)
|
||||
- [Streaming MAVLink messages](../mavlink/streaming_messages.md)
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||||
- [Handling incoming MAVLink messages (and writing to a uORB topic)](../mavlink/receiving_messages.md)
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||||
- [Custom MAVLink Messages](../mavlink/custom_messages.md)
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||||
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||||
::: info
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||||
We do not yet cover _command_ handling and sending, or how to implement your own microservices.
|
||||
:::
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||||
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||||
## MAVLink Overview
|
||||
|
||||
MAVLink is a lightweight protocol that was designed for efficiently sending messages over unreliable low-bandwidth radio links.
|
||||
|
||||
_Messages_ are simplest and most "fundamental" definition in MAVLink, consisting of a name (e.g. [ATTITUDE](https://mavlink.io/en/messages/common.html#ATTITUDE)), id, and fields containing relevant data.
|
||||
They are deliberately lightweight, with a constrained size, and no semantics for resending and acknowledgement.
|
||||
Stand-alone messages are commonly used for streaming telemetry or status information, and for sending commands where no acknowledgement is required - such as setpoint commands sent at high rate.
|
||||
|
||||
The [Command Protocol](https://mavlink.io/en/services/command.html) is a higher level protocol for sending commands that may need acknowledgement.
|
||||
Specific commands are defined as values of the [MAV_CMD](https://mavlink.io/en/messages/common.html#mav_commands) enumeration, such as the takeoff command [MAV_CMD_NAV_TAKEOFF](https://mavlink.io/en/messages/common.html#MAV_CMD_NAV_TAKEOFF), and include up to 7 numeric "param" values.
|
||||
The protocol sends a command by packaging the parameter values in a `COMMAND_INT` or `COMMAND_LONG` message, and waits for an acknowledgement with a result in a `COMMAND_ACK`.
|
||||
The command is resent automatically if no acknowledgment is received.
|
||||
Note that [MAV_CMD](https://mavlink.io/en/messages/common.html#mav_commands) definitions are also used to define mission actions, and that not all definitions are supported for use in commands/missions on PX4.
|
||||
|
||||
[Microservices](https://mavlink.io/en/services/) are other higher level protocols built on top of MAVLink messages.
|
||||
They are used to communicate information that cannot be sent in a single message, and to deliver features such as reliable communication.
|
||||
The command protocol described above is one such service.
|
||||
Others include the [File Transfer Protocol](https://mavlink.io/en/services/ftp.html), [Camera Protocol](https://mavlink.io/en/services/camera.html) and [Mission Protocol](https://mavlink.io/en/services/mission.html).
|
||||
|
||||
MAVLink messages, commands and enumerations are defined in [XML definition files](https://mavlink.io/en/guide/define_xml_element.html).
|
||||
The MAVLink toolchain includes code generators that create programming-language-specific libraries from these definitions for sending and receiving messages.
|
||||
Note that most generated libraries do not create code to implement microservices.
|
||||
|
||||
The MAVLink project standardizes a number of messages, commands, enumerations, and microservices, for exchanging data using the following definition files (note that higher level files _include_ the definitions of the files below them):
|
||||
|
||||
- [development.xml](https://mavlink.io/en/messages/development.html) — Definitions that are proposed to be part of the standard.
|
||||
The definitions move to `common.xml` if accepted following testing.
|
||||
- [common.xml](https://mavlink.io/en/messages/common.html) — A "library" of definitions meeting many common UAV use cases.
|
||||
These are supported by many flight stacks, ground stations, and MAVLink peripherals.
|
||||
Flight stacks that use these definitions are more likely to interoperate.
|
||||
- [standard.xml](https://mavlink.io/en/messages/standard.html) — Definitions that are actually standard.
|
||||
They are present on the vast majority of flight stacks and implemented in the same way.
|
||||
- [minimal.xml](https://mavlink.io/en/messages/minimal.html) — Definitions required by a minimal MAVLink implementation.
|
||||
|
||||
The project also hosts [dialect XML definitions](https://mavlink.io/en/messages/#dialects), which contain MAVLink definitions that are specific to a flight stack or other stakeholder.
|
||||
|
||||
The protocol relies on each end of the communication having a shared definition of what messages are being sent.
|
||||
What this means is that in order to communicate both ends of the communication must use libraries generated from the same XML definition.
|
||||
|
||||
<!--
|
||||
The messages are sent over-the-wire in the "payload" of a [MAVLink packet](https://mavlink.io/en/guide/serialization.html#mavlink2_packet_format).
|
||||
In order to reduce the amount of information that must be sent, the packet does not include the message metadata, such as what fields are in the message and so on.
|
||||
Instead, the fields are serialized in a predefined order based on data size and XML definition order, and MAVLink relies on each end of the communication having a shared definition of what messages are being sent.
|
||||
The shared identity of the message is conveyed by the message id, along with a CRC ("`CRC_EXTRA`") that uniquely identifies the message based on its name and id, and the field names and types.
|
||||
The receiving end of the communication will discard any packet for which the message id and the `CRC_EXTRA` do not match.
|
||||
-->
|
||||
|
||||
## PX4 and MAVLink
|
||||
|
||||
PX4 releases build `common.xml` MAVLink definitions by default, for the greatest compatibility with MAVLink ground stations, libraries, and external components such as MAVLink cameras.
|
||||
In the `main` branch, these are included from `development.xml` on SITL, and `common.xml` for other boards.
|
||||
|
||||
::: info
|
||||
To be part of a PX4 release, any MAVLink definitions that you use must be in `common.xml` (or included files such as `standard.xml` and `minimal.xml`).
|
||||
During development you can use definitions in `development.xml`.
|
||||
You will need to work with the [MAVLink team](https://mavlink.io/en/contributing/contributing.html) to define and contribute these definitions.
|
||||
:::
|
||||
|
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PX4 includes the [mavlink/mavlink](https://github.com/mavlink/mavlink) repo as a submodule under [/src/modules/mavlink](https://github.com/PX4/PX4-Autopilot/tree/main/src/modules/mavlink).
|
||||
This contains XML definition files in [/mavlink/messages/1.0/](https://github.com/mavlink/mavlink/blob/master/message_definitions/v1.0/).
|
||||
|
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The build toolchain generates the MAVLink 2 C header files at build time.
|
||||
The XML file for which headers files are generated may be defined in the [PX4 kconfig board configuration](../hardware/porting_guide_config.md#px4-board-configuration-kconfig) on a per-board basis, using the variable `CONFIG_MAVLINK_DIALECT`:
|
||||
|
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- For SITL `CONFIG_MAVLINK_DIALECT` is set to `development` in [boards/px4/sitl/default.px4board](https://github.com/PX4/PX4-Autopilot/blob/main/boards/px4/sitl/default.px4board#L36).
|
||||
You can change this to any other definition file, but the file must include `common.xml`.
|
||||
- For other boards `CONFIG_MAVLINK_DIALECT` is not set by default, and PX4 builds the definitions in `common.xml` (these are build into the [mavlink module](../modules/modules_communication.md#mavlink) by default — search for `menuconfig MAVLINK_DIALECT` in [src/modules/mavlink/Kconfig](https://github.com/PX4/PX4-Autopilot/blob/main/src/modules/mavlink/Kconfig#L10)).
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The files are generated into the build directory: `/build/<build target>/mavlink/`.
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<Redirect to="../mavlink/" />
|
||||
|
||||
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Block a user