PX4 自动驾驶用户指南 (v1.14)

# uXRCE-DDS (PX4-ROS 2/DDS Bridge)

注解

uXRCE-DDS replaces the Fast-RTPS Bridge (opens new window) used in PX4 v1.13. If you were using the Fast-RTPS Bridge, please follow the migration guidelines.

PX4 uses uXRCE-DDS middleware to allow uORB messages to be published and subscribed on a companion computer as though they were ROS 2 topics. 该特性可支持PX4和ROS2之间的快速、可靠的集成， 并且使ROS2应用程序更容易获得飞行器信息并向其发送命令。

PX4 使用 eProsima Micro XRCE-DDS (opens new window) 来实现XRCE-DDS。

本指南描述了软件架构以及建立客户和代理所需要的操作。 尤其是，它涵盖了对于PX4用户最重要的选项。

# 软件架构

The uXRCE-DDS middleware consists of a client running on PX4 and an agent running on the companion computer, with bi-directional data exchange between them over a serial or UDP link. 代理端(Agent)充当客户端的代理，使其能够在DDS全局数据空间中发布和订阅话题。

Architecture uXRCE-DDS with ROS 2

In order for PX4 uORB topics to be shared on the DDS network you will need uXRCE-DDS client running on PX4, connected to the micro XRCE-DDS agent running on the companion.

The PX4 uxrce_dds_client publishes to/from a defined set of uORB topics to the global DDS data space.

The eProsima micro XRCE-DDS agent (opens new window) runs on the companion computer and acts as a proxy for the client in the DDS/ROS 2 network.

代理(Agent)本身不依赖客户端测代码，可以独立于PX4或ROS编译或安装。

Code that wants to subscribe/publish to PX4 does have a dependency on client-side code; it requires uORB message definitions that match those used to create the PX4 uXRCE-DDS client so that it can interpret the messages.

# 代码生成

The PX4 uxrce_dds_client is generated at build time and included in PX4 firmare by default. 代理不依赖客户端代码。 它可以单独构建或在ROS2工作区中构建，也可以在Ubuntu上采用snap包安装。

When PX4 is built, a code generator uses the uORB message definitions in the source tree (PX4-Autopilot/msg (opens new window)) to compile support for the subset of uORB topics in PX4-Autopilot/src/modules/uxrce_dds_client/dds_topics.yaml (opens new window) into uxrce_dds_client.

PX4 main分支或release版本构建将自动从当前分支的 PX4/px4_msgs (opens new window) 中导出 uORB 消息子集。

ROS 2 applications need to be built in a workspace that includes the same message definitions that were used to create the uXRCE-DDS client module in the PX4 Firmware. 可以通过将接口包 PX4/px4_msgs (opens new window) 克隆到你的 ROS 2 工作空间并切换到正确的分支来实现。 请注意，所有与消息相关联的代码生成都是由 ROS 2 处理的。

# Micro XRCE-DDS Agent Installation

The Micro XRCE-DDS Agent can be installed on the companion computer using a binary package, built and installed from source, or built and run from within a ROS 2 workspace. 所有这些方法都需要获取 全部 与客户端通信所需的依赖项 (例如FastCDR)。

注解

The official (and more complete) installation guide is the Eprosima: micro XRCE-DDS Installation Guide (opens new window). This section summarises the options that have been tested with PX4 during creation of these docs.

# 源码安装

在 Ubuntu 上，您可以使用以下命令从源代码构建并单独安装代理：

git clone https://github.com/eProsima/Micro-XRCE-DDS-Agent.git
cd Micro-XRCE-DDS-Agent
mkdir build
cd build
cmake ...
make
sudo make installing
sudo ldconfig /usr/local/lib/

注解

在 官方指南 (opens new window)中有从相应主题链接的各种构建配置选项， 但尚未对其进行测试。

To start the agent with settings for connecting to the uXRCE-DDS client running on the simulator:

MicroXRCEAgent udp4 -p 8888

# 从 Snap 软件包安装

使用以下命令从 Ubuntu 的 snap 软件包安装：

sudo snap install microxrce-ds-agent --edge

To start the agent with settings for connecting to the uXRCE-DDS client running on the simulator (note that the command name is different than if you build the agent locally):

micro-xrce-dds-agent udp4 -p 8888

注解

在编写该文档时，从snap仓库安装的稳定版本在与PX4连接时会报创建话题错误。 开发版本(使用 --edge 控制字段获取安装)可以正常工作。

# Build/Run within ROS 2 Workspace

The agent can be built and launched within a ROS 2 workspace (or build standalone and launched from a workspace. You must already have installed ROS 2 following the instructions in: ROS 2 User Guide > Install ROS 2.

To build the agent within ROS:

  1. Create a workspace directory for the agent:

    mkdir -p ~/px4_ros_uxrce_dds_ws/src

  2. Clone the source code for the eProsima Micro-XRCE-DDS-Agent (opens new window) to the /src directory (the main branch is cloned by default):

    cd ~/px4_ros_uxrce_dds_ws/src
git clone https://github.com/eProsima/Micro-XRCE-DDS-Agent.git

  3. Source the ROS 2 development environment, and compile the workspace using colcon:

    :::

    : :::

    This builds all the folders under /src using the sourced toolchain.

    To run the micro XRCE-DDS agent in the workspace:

    1. Source the local_setup.bash to make the executables available in the terminal (also setup.bash if using a new terminal).

      :::

      : :::

      1. Start the agent with settings for connecting to the uXRCE-DDS client running on the simulator:

        MicroXRCEAgent udp4 -p 8888

      # Starting Agent and Client

      # Starting the Agent

      The agent is used to connect to the client over a particular channel, such as UDP or a serial connection. The channel settings are specified when the agent is started, using command line options. These are documented in the eProsima user guide: Micro XRCE-DDS Agent > Agent CLI (opens new window). Note that the agent supports many channel options, but PX4 only supports UDP and serial connections.

      注解

      You should create a single instance of the agent for each channel over which you need to connect.

      For example, the PX4 simulator runs the uXRCE-DDS client over UDP on port 8888, so to connect to the simulator you would start the agent with the command:

      MicroXRCEAgent udp4 -p 8888

      When working with real hardware, the setup depends on the hardware, OS, and channel. For example, if you're using the RasPi UART0 serial port, you might connect using this command (based on the information in Raspberry Pi Documentation > Configuring UARTS (opens new window)):

      sudo MicroXRCEAgent serial --dev /dev/AMA0 -b 921600

      注解

      For more information about setting up communications channels see Pixhawk + Companion Setup > Serial Port setup, and sub-documents.

      # Starting the Client

      The uXRCE-DDS client module (uxrce_dds_client) is included by default in all firmware and the simulator. This must be started with appropriate settings for the communication channel that you wish to use to communicate with the agent.

      注解

      The simulator automatically starts the client on localhost UDP port 8888 using the default uxrce-dds namespace.

      The configuration can be done using the UXRCE-DDS parameters:

      • UXRCE_DDS_CFG: Set the port to connect on, such as TELEM2, Ethernet, or Wifi.

      • If using an Ethernet connection:

        • UXRCE_DDS_PRT: Use this to specify the agent UDP listening port. The default value is 8888.

        • UXRCE_DDS_AG_IP: Use this to specify the IP address of the agent. The IP address must be provided in int32 format as PX4 does not support string parameters. The default value is 2130706433 which corresponds to the localhost 127.0.0.1.

          You can use Tools/convert_ip.py (opens new window) to convert between the formats:

          • To obtain the int32 version of an IP in decimal dot notation the command is:

            python3 ./PX4-Autopilot/Tools/convert_ip.py <the IP address in decimal dot notation>

          • To get the IP address in decimal dot notation from the int32 version:

            python3 ./PX4-Autopilot/Tools/convert_ip.py -r <the IP address in int32 notation>

      • If using a serial connection:

        • SER_TEL2_BAUD, SER_URT6_BAUD (and so on): Use the _BAUD parameter associated with the serial port to set the baud rate. For example, you'd set a value for SER_TEL2_BAUD if you are connecting to the companion using TELEM2. For more information see Serial port configuration.

      • Some setups might also need these parameters to be set:

        • UXRCE_DDS_KEY: The uXRCE-DDS key. If you're working in a multi-client, single agent configuration, each client should have a unique non-zero key. This is primarily important for multi-vehicle simulations, where all clients are connected in UDP to the same agent. (See the official eprosima documentation (opens new window) , uxr_init_session.)
        • UXRCE_DDS_DOM_ID: The DDS domain ID. This provides a logical separation between DDS networks, and can be used to separate clients on different networks. By default, ROS 2 operates on ID 0.

      注解

      Many ports are already have a default configuration. To use these ports you must first disable the existing configuration:

      Once set, you may need to reboot PX4 for the parameters to take effect. They will then persist through subsequent reboots.

      You can also start the uxrce_dds_client using a command line. This can be called as part of System Startup or through the MAVLink Shell (or a system console). This method is useful when you need to set a custom client namespace, as no parameter is provided for this purpose. For example, the following command can be used to connect via Ethernet to a remote host at 192.168.0.100:8888 and to set the client namespace to /drone/.

      uxrce_dds_client start -t udp -p 8888 -h 192.168.0.100 -n drone

      Options -p or -h are used to bypass UXRCE_DDS_PRT and UXRCE_DDS_AG_IP.

      # Starting the Client in Simulation

      The simulator startup logic (init.d-posix/rcS (opens new window)) uses the client startup commands for single and multi vehicle simulations, enabling the setting of appropriate instance ids and DDS namespaces. By default the client is started on localhost UDP port 8888 with no additional namespace.

      Environment variables are provided that override some UXRCE-DDS parameters. These allow users to create custom startup files for their simulations:

      For example, the following command can be used to start a Gazebo simulation with che client operating on the DDS domain 3, port 9999 and topic namespace drone.

      ROS_DOMAIN_ID=3 PX4_UXRCE_DDS_PORT=9999 PX4_UXRCE_DDS_NS=drone make px4_sitl gz_x500

      # Supported uORB Messages

      The set of PX4 uORB topics that are exposed through the client are set in dds_topics.yaml (opens new window).

      The topics are release specific (support is compiled into uxrce_dds_client at build time). While most releases should support a very similar set of messages, to be certain you would need to check the yaml file for your particular release.

      Note that ROS 2/DDS needs to have the same message definitions that were used to create the uXRCE-DDS client module in the PX4 Firmware in order to interpret the messages. The message definitions are stored in the ROS 2 interface package PX4/px4_msgs (opens new window), and they are automatically synchronized by CI on the main and release branches. Note that all the messages from PX4 source code are present in the repository, but only those listed in dds_topics.yaml will be available as ROS 2 topics. Therefore,

      • If you're using a main or release version of PX4 you can get the message definitions by cloning the interface package PX4/px4_msgs (opens new window) into your workspace.

      • If you're creating or modifying uORB messages you must manually update the messages in your workspace from your PX4 source tree. Generally this means that you would update dds_topics.yaml (opens new window), clone the interface package, and then manually synchronize it by copying the new/modified message definitions from PX4-Autopilot/msg (opens new window) to its msg folders. Assuming that PX4-Autopilot is in your home directory ~, while px4_msgs is in ~/px4_ros_com/src/, then the command might be:

        rm ~/px4_ros_com/src/px4_msgs/msg/*.msg
cp ~/PX4-Autopilot/mgs/*.msg ~/px4_ros_com/src/px4_msgs/msg/

      注解

      Technically, dds_topics.yaml (opens new window) completely defines the relationship between PX4 uORB topics and ROS 2 messages. For more information see DDS Topics YAML below.

      # Customizing the Topic Namespace

      Custom topic namespaces can be applied at build time (changing dds_topics.yaml (opens new window)) or at runtime (which is useful for multi vehicle operations):

      • One possibility is to use the -n option when starting the uxrce_dds_client from command line. This technique can be used both in simulation and real vehicles.
      • A custom namespace can be provided for simulations (only) by setting the environment variable PX4_UXRCE_DDS_NS before starting the simulation.

      注解

      Changing the namespace at runtime will append the desired namespace as a prefix to all topic fields in dds_topics.yaml (opens new window). Therefore, commands like:

      uxrce_dds_client start -n uav_1

      or

      PX4_UXRCE_DDS_NS=uav_1 make px4_sitl gz_x500

      will generate topics under the namespaces:

      /uav_1/fmu/in/  # for subscribers
/uav_1/fmu/out/ # for publishers

      # PX4 ROS 2 QoS Settings

      PX4 QoS settings for publishers are incompatible with the default QoS settings for ROS 2 subscribers. So if ROS 2 code needs to subscribe to a uORB topic, it will need to use compatible QoS settings. One example of which is shown in ROS 2 User Guide > ROS 2 Subscriber QoS Settings.

      PX4 uses the following QoS settings for publishers:

      uxrQoS_t qos = {
  .durability = UXR_DURABILITY_TRANSIENT_LOCAL,
  .reliability = UXR_RELIABILITY_BEST_EFFORT,
  .history = UXR_HISTORY_KEEP_LAST,
  .depth = 0,
};

      PX4 uses the following QoS settings for subscribers:

      uxrQoS_t qos = {
  .durability = UXR_DURABILITY_VOLATILE,
  .reliability = UXR_RELIABILITY_BEST_EFFORT,
  .history = UXR_HISTORY_KEEP_LAST,
  .depth = queue_depth,
};

      ROS 2 uses the following QoS settings (by default) for publishers and subscriptions: "keep last" for history with a queue size of 10, "reliable" for reliability, "volatile" for durability, and "system default" for liveliness. Deadline, lifespan, and lease durations are also all set to "default".

      # DDS Topics YAML

      The PX4 yaml file dds_topics.yaml (opens new window) defines the set of PX4 uORB topics that are built into firmware and published. More precisely, it completely defines the relationship/pairing between PX4 uORB and ROS 2 messages.

      The file is structured as follows:

      publications:

  - topic: /fmu/out/collision_constraints
    type: px4_msgs::msg::CollisionConstraints

  ...

  - topic: /fmu/out/vehicle_odometry
    type: px4_msgs::msg::VehicleOdometry

  - topic: /fmu/out/vehicle_status
    type: px4_msgs::msg::VehicleStatus

  - topic: /fmu/out/vehicle_trajectory_waypoint_desired
    type: px4_msgs::msg::VehicleTrajectoryWaypoint

subscriptions:

  - topic: /fmu/in/offboard_control_mode
    type: px4_msgs::msg::OffboardControlMode

  ...

  - topic: /fmu/in/vehicle_trajectory_waypoint
    type: px4_msgs::msg::VehicleTrajectoryWaypoint

      Each (topic,type) pairs defines:

      1. A new subscription or publication depending on the list to which it is added.
      2. The topic base name, which must coincide with the desired uORB topic name that you want to publish/subscribe. It is identified by the last token in topic: that starts with / and does not contains any / in it. vehicle_odometry, vehicle_status and offboard_control_mode are examples of base names.
      3. The topic namespace (opens new window). By default it is set to:
        • /fmu/out/ for topics that are published by PX4.
        • /fmu/in/ for topics that are subscribed by PX4.
      4. The message type (VehicleOdometry, VehicleStatus, OffboardControlMode, etc.) and the ROS 2 package (px4_msgs) that is expected to provide the message definition.

      You can arbitrarily change the configuration. For example, you could use different default namespaces or use a custom package to store the message definitions.

      # Fast-RTPS to uXRCE-DDS Migration Guidelines

      These guidelines explain how to migrate from using PX4 v1.13 Fast-RTPS middleware to PX4 v1.14 uXRCE-DDS middleware. These are useful if you have ROS 2 applications written for PX4 v1.13 (opens new window), or you have used Fast-RTPS to interface your applications to PX4 directly (opens new window).

      注解

      This section contains migration-specific information. You should also read the rest of this page to properly understand uXRCE-DDS.

      # Dependencies do not need to be removed

      uXRCE-DDS does not need the dependencies that were required for Fast-RTPS, such as those installed by following the topic Fast DDS Installation (opens new window). You can keep them if you want, without affecting your uXRCE-DDS applications.

      If you do choose to remove the dependencies, take care not to remove anything that is used by applications (for example, Java).

      # _rtps targets have been removed

      Anywhere you previously used a build target with extension _rtps, such as px4_fmu-v5_rtps or px4_sitl_rtps, you can now use the equivalent default target (for these cases px4_fmu-v5_default and px4_sitl_default).

      The make targets with extension _rtps were used to build firmware that included client side RTPS code. The uXRCE-DDS middleware is included by default in builds for most boards, so you no longer need a special firmware to work with ROS 2.

      To check if your board has the middleware, look for CONFIG_MODULES_UXRCE_DDS_CLIENT=y in the .px4board file of your board. Those files are nested in PX4-Autopilot/boards (opens new window).

      If it is not present, or if it is set to n, then you have to clone the PX4 repo, modify the board configuration and manually compile the firmware.

      # New client module and new start parameters

      As the client is implemented by a new PX4 module, you now have new parameters to start it. Take a look at the client startup section to learn how this is done.

      # New file for setting which topics are published

      The list of topics that are published and subscribed for a particular firmware is now managed by the dds_topic.yaml (opens new window) configuration file, which replaces urtps_bridge_topics.yaml (opens new window)

      See Supported uORB Messages and DDS Topics YAML sections for more information.

      # Topics no longer need to be synced between client and agent.

      The list of bridged topics between agent and client no longer needs to be synced for ROS 2, so the update_px4_ros2_bridge.sh script is no longer needed.

      # Default topic naming convention has changed

      The topic naming format changed:

      • Published topics: /fmu/topic-name/out (Fast-RTPS) to /fmu/out/topic-name (XRCE-DDS).
      • Subscribed topics: /fmu/topic-name/in(Fast-RTPS) to /fmu/in/topic-name (XRCE-DDS).

      You should update your application to the new convention.

      注解

      You might also edit dds_topic.yaml (opens new window) to revert to the old convention. This is not recommended because it means that you would have to always use custom firmware.

      # XRCE-DDS-Agent

      The XRCE-DDS agent is "generic" and independent of PX4: micro-xrce-dds-agent (opens new window). There are many ways to install it on your PC / companion computer - for more information see the dedicated section.

      # Application-Specific Changes

      If you where not using ROS 2 alongside the agent (Fast DDS Interface ROS-Independent (opens new window)), then you need to migrate to eProsima Fast DDS (opens new window).

      ROS 2 applications still need to compile alongside the PX4 messages, which you do by adding the px4_msgs (opens new window) package to your workspace. You can remove the px4_ros_com (opens new window) package as it is no longer needed, other than for example code.

      In your ROS 2 nodes, you will need to:

      • Update the QoS of your publishers and subscribers as PX4 does not use the ROS 2 default settings.

      • Change the names of your topics, unless you edited dds_topic.yaml (opens new window).

      • Remove everything related to time synchronization, as XRCE-DDS automatically takes care of agent/client time synchronization.

        In C++ applications you can set the timestamp field of your messages like this:

        msg.timestamp = this->get_clock()->now().nanoseconds() / 1000;

        In Python applications you can set the timestamp field of your messages like this:

        msg.timestamp = int(self.get_clock().now().nanoseconds / 1000)

      # Helpful Resources

      # Setting up the bridge with real hardware

      This section is work-in-progress.

      # Troubleshooting

      # Client reports that selected UART port is busy

      If the selected UART port is busy, it's possible that the MAVLink application is already being used. If both MAVLink and RTPS connections are required you will have to either move the connection to use another port or using the available protocol splitter for PX4 and companion computers.

      提示

      A quick/temporary fix to allow bridge testing during development is to stop MAVLink from NuttShell:

      mavlink stop-all

      # Enable UART on a companion computer

      For UART transport on a Raspberry Pi or any other companion computer you will have to enable the serial port:

      1. Make sure the userid (default is pi on a Raspberry Pi) is a member of the dialout group:

        groups pi
sudo usermod -a -G dialout pi

      2. For the Raspberry Pi in particular, you need to stop the GPIO serial console that is using the port:

        sudo raspi-config

        In the menu showed go to Interfacing options > Serial. Select NO for Would you like a login shell to be accessible over serial?. Valid and reboot.

      3. Check UART in kernel:

        sudo vi /boot/config.txt

        And make sure that the enable_uart value is set to 1:

         enable_uart=1

      -->

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