ardupilot/libraries/AP_DDS

Testing with DDS/micro-Ros

Architecture

Ardupilot contains the DDS Client library, which can run as SITL. Then, the DDS application runs a ROS2 node, an EProsima Integration Service, and the MicroXRCE Agent. The two systems communicate can communicate over serial or UDP.

---
title: UDP Loopback
---
graph LR

  subgraph Linux Computer

    subgraph Ardupilot SITL
      veh[sim_vehicle.py] <--> xrceClient[EProsima Micro XRCE DDS Client]
      xrceClient <--> port1[udp:2019]
    end

    subgraph DDS Application
      ros[ROS2 Node] <--> agent[Micro ROS Agent]
      agent <-->port1[udp:2019]
    end

    loopback

  end

---
title: Hardware Serial Port Loopback
---
graph LR

  subgraph Linux Computer

    subgraph Ardupilot SITL
      veh[sim_vehicle.py] <--> xrceClient[EProsima Micro XRCE DDS Client]
      xrceClient <--> port1[devUSB1]
    end

    subgraph DDS Application
      ros[ROS2 Node] <--> agent[Micro ROS Agent]
      agent <--> port2[devUSB2]
    end

    port1 <--> port2

  end

Installing Build Dependencies

While DDS support in Ardupilot is mostly through git submodules, another tool needs to be available on your system: Micro XRCE DDS Gen.

• Go to a directory on your system to clone the repo (perhaps next to ardupilot)

• Install java

  sudo apt install default-jre
  

• Follow instructions here to install the latest version of the generator using Ardupilot's mirror

  git clone --recurse-submodules https://github.com/ardupilot/Micro-XRCE-DDS-Gen.git
  cd Micro-XRCE-DDS-Gen
  ./gradlew assemble
  

• Add the generator directory to $PATH.

  # Add this to ~/.bashrc
  
  export PATH=$PATH:/your/path/to/Micro-XRCE-DDS-Gen/scripts
  

• Test it

  cd /path/to/ardupilot
  microxrceddsgen -version
  # openjdk version "11.0.18" 2023-01-17
  # OpenJDK Runtime Environment (build 11.0.18+10-post-Ubuntu-0ubuntu122.04)
  # OpenJDK 64-Bit Server VM (build 11.0.18+10-post-Ubuntu-0ubuntu122.04, mixed mode, sharing)
  # microxrceddsgen version: 1.0.0beta2
  

⚠️ If you have installed FastDDS or FastDDSGen globally on your system: eProsima's libraries and the packaging system in Ardupilot are not determistic in this scenario. You may experience the wrong version of a library brought in, or runtime segfaults. For now, avoid having simultaneous local and global installs. If you followed the global install section, you should remove it and switch to local install.

Serial Only: Set up serial for SITL with DDS

On Linux, creating a virtual serial port will be necessary to use serial in SITL, because of that install socat.

sudo apt-get update
sudo apt-get install socat

Setup ardupilot for SITL with DDS

Set up your SITL. Run the simulator with the following command. If using UDP, the only parameter you need to set it DDS_ENABLE.

Name	Description
DDS_ENABLE	Set to 1 to enable DDS
SERIAL1_BAUD	The serial baud rate for DDS
SERIAL1_PROTOCOL	Set this to 45 to use DDS on the serial port

# Wipe params till you see "AP: ArduPilot Ready"
# Select your favorite vehicle type
sim_vehicle.py -w -v ArduPlane --console -DG --enable-dds

# Enable DDS (both for UDP or Serial)
param set DDS_ENABLE 1

# Only for Serial
param set SERIAL1_BAUD 115
# See libraries/AP_SerialManager/AP_SerialManager.h AP_SerialManager SerialProtocol_DDS_XRCE
param set SERIAL1_PROTOCOL 45

Because DDS_ENABLE requires a reboot, stop the simulator with ctrl+C and proceed to the next section.

Setup ROS 2 and micro-ROS

Follow the steps to use the microROS Agent

• Install ROS Humble (as described here)

  • https://docs.ros.org/en/humble/Installation/Ubuntu-Install-Debians.html

• Install geographic_msgs

  sudo apt install ros-humble-geographic-msgs
  

• Install and run the microROS agent (as descibed here). Make sure to use the humble branch.

  • Follow the instructions for the following:

    • Do "Installing ROS 2 and the micro-ROS build system"
      • Skip the docker run command, build it locally instead
    • Skip "Creating a new firmware workspace"
    • Skip "Building the firmware"
    • Do "Creating the micro-ROS agent"
    • Source your ROS workspace

Until this PR is merged, ignore the notes about foxy. It works on humble.

Using the ROS2 CLI to Read Ardupilot Data

After your setups are complete, do the following:

• Source the ros2 installation

  source /opt/ros/humble/setup.bash
  

Next, follow the associated section for your chosen transport, and finally you can use the ROS 2 CLI.

UDP (recommended for SITL)

• Run the microROS agent

  cd ardupilot/libraries/AP_DDS
  ros2 run micro_ros_agent micro_ros_agent udp4 -p 2019 -r dds_xrce_profile.xml
  

• Run SITL (remember to kill any terminals running ardupilot SITL beforehand)

  sim_vehicle.py -v ArduPlane -DG --console --enable-dds
  

Serial

• Start a virtual serial port with socat. Take note of the two /dev/pts/* ports. If yours are different, substitute as needed.

  socat -d -d pty,raw,echo=0 pty,raw,echo=0
  >>> 2023/02/21 05:26:06 socat[334] N PTY is /dev/pts/1
  >>> 2023/02/21 05:26:06 socat[334] N PTY is /dev/pts/2
  >>> 2023/02/21 05:26:06 socat[334] N starting data transfer loop with FDs [5,5] and [7,7]
  

• Run the microROS agent

  cd ardupilot/libraries/AP_DDS
  # assuming we are using tty/pts/2 for DDS Application
  ros2 run micro_ros_agent micro_ros_agent serial -b 115200  -r dds_xrce_profile.xml -D /dev/pts/2
  

• Run SITL (remember to kill any terminals running ardupilot SITL beforehand)

  # assuming we are using /dev/pts/1 for Ardupilot SITL
  sim_vehicle.py -v ArduPlane -DG --console --enable-dds -A "--uartC=uart:/dev/pts/1"
  

Use ROS 2 CLI

• You should be able to see the agent here and view the data output.

  $ ros2 node list
  /Ardupilot_DDS_XRCE_Client
  
  $ ros2 topic list  -v
  Published topics:
  * /ap/battery/battery0 [sensor_msgs/msg/BatteryState] 1 publisher
  * /ap/clock [rosgraph_msgs/msg/Clock] 1 publisher
  * /ap/geopose/filtered [geographic_msgs/msg/GeoPoseStamped] 1 publisher
  * /ap/navsat/navsat0 [sensor_msgs/msg/NavSatFix] 1 publisher
  * /ap/pose/filtered [geometry_msgs/msg/PoseStamped] 1 publisher
  * /ap/tf_static [tf2_msgs/msg/TFMessage] 1 publisher
  * /ap/time [builtin_interfaces/msg/Time] 1 publisher
  * /ap/twist/filtered [geometry_msgs/msg/TwistStamped] 1 publisher
  * /parameter_events [rcl_interfaces/msg/ParameterEvent] 1 publisher
  * /rosout [rcl_interfaces/msg/Log] 1 publisher
  
  Subscribed topics:
  * /ap/joy [sensor_msgs/msg/Joy] 1 subscriber
  * /ap/tf [tf2_msgs/msg/TFMessage] 1 subscriber
  * /ap/cmd_vel [geometry_msgs/msg/TwistStamped] 1 subscriber
  
  $ ros2 topic hz /ap/time
  average rate: 50.115
          min: 0.012s max: 0.024s std dev: 0.00328s window: 52
  
  $ ros2 topic echo /ap/time
  sec: 1678668735
  nanosec: 729410000
  
  $ ros2 service list
  /arm_motors
  ---
  

  The static transforms for enabled sensors are also published, and can be recieved like so:

  ros2 topic echo /ap/tf_static --qos-depth 1 --qos-history keep_last --qos-reliability reliable --qos-durability transient_local --once
  

  In order to consume the transforms, it's highly recommended to create and run a transform broadcaster in ROS 2.

Using ROS 2 services (with Integration Services)

Prerequisites

• Install and setup Micro-XRCE Agent
• Install and setup Integration Services (it would be good to have a separate workspace for this)
  • Get System Handles for ROS 2
  • Get System Handles for Fast-DDS
• Once the above-mentioned System Handles have been cloned, build the Integration Services with the following command : colcon build --cmake-args -DMIX_ROS_PACKAGES="example_interfaces ardupilot_msgs"

Setup

• The necessary ROS 2 messages and service defintions (especially for the Arming/Disarming Services) are already defined in the ardupilot_msgs folder in the Tools directory.

Terminal 1 (XRCE Agent)

• Move to the AP_DDS folder and run the XRCE Agent as follows MicroXRCEAgent udp4 -p 2019 -r dds_xrce_profile.xml

Terminal 2 (Integration Service)

• Source ROS 2 installation
• Source Integration Service installation
• Move to the AP_DDS folder and run the following command integration-service Is-Config/Arm_Motors_DDS_IS_config.yaml

Terminal 3 (Ardupilot)

• Make sure you have successfully setup Ardupilot and the DDS_ENABLE param is set to 1
• Run SITL with the following command sim_vehicle.py -v ArduPlane -DG --console --enable-dds

Terminal 4 (ROS 2 Client)

• Run the following command : ros2 service call /arm_motors ardupilot_msgs/srv/ArmMotors "{arm: True}"

Contributing to AP_DDS library

Adding DDS messages to Ardupilot

Unlike the use of ROS 2 .msg files, since Ardupilot supports native DDS, the message files follow OMG IDL DDS v4.2. This package is intended to work with any .idl file complying with those extensions.

Over time, these restrictions will ideally go away.

To get a new IDL file from ROS2, follow this process:

cd ardupilot
source /opt/ros/humble/setup.bash
# Find the IDL file
find /opt/ros/$ROS_DISTRO -type f -wholename \*builtin_interfaces/msg/Time.idl
# Create the directory in the source tree if it doesn't exist similar to the one found in the ros directory
mkdir -p libraries/AP_DDS/Idl/builtin_interfaces/msg/
# Copy the IDL
cp /opt/ros/humble/share/builtin_interfaces/msg/Time.idl libraries/AP_DDS/Idl/builtin_interfaces/msg/
# Build the code again with the `--enable-dds` flag as described above

Development Requirements

Astyle is used to format the C++ code in AP_DDS. This is required for CI to pass the build. See Tools/CodeStyle/ardupilot-astyle.sh.

./Tools/CodeStyle/ardupilot-astyle.sh libraries/AP_DDS/*.h libraries/AP_DDS/*.cpp

Pre-commit is used for other things like formatting python and XML code. This will run the tools automatically when you commit. If there are changes, just add them back your staging index and commit again.

1. Install pre-commit python package.
2. Install ArduPilot's hooks in the root of the repo, then commit like normal

cd ardupilot
pre-commit install
git commit