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CycloneDDS and Unicast - Solutions for missing ROS2 topics

CycloneDDS and Unicast

Had an ongoing issue with the robot where ros2 topic list shows only 2 topics, when I did usb0 interface down then up it would sometimes help, sometimes not. The error can be seen in the create3 logs in the web interface:

user.notice create-platform: 1742579888.164076 [0] tev: ddsi_udp_conn_write to udp/239.255.0.1:7400 failed with retcode -1

This suggests that ROS 2’s DDS (Data Distribution Service) communication is failing. The address 239.255.0.1:7400 is a multicast address used by DDS for discovery and communication.

Solution with Unicast and FastDDS server - Not used

To try and fix this, and given the robot only needs to communicate with the RaspberryPi, I tried to run this on a screen in the raspberry pi:

fastdds discovery -i 0 -l <rpi_ip> -p 11811

And in the create3 web interface I turned on Enable Fast DDS discovery server? and gave it the following address: <rpi_ip>:11811. Also added the following to .bashrc on the raspberry pi so nodes on the pi can communicate:

export ROS_DISCOVERY_SERVER=<rpi_ip>:11811

This works when used with FastDDS, however Vizanti does not work with this RMW implementation, so I needed to switch back to CycloneDDS

Here is an example online that might work better: FastDDS. The problem with Vizanti is to do with missing ros-humble-rmw-fastrtps-dynamic-cpp package.

Fixing CycloneDDS

The solution that worked for me in the end was to use the following setting in the cyclonedds.xml configuration file:

<AllowMulticast>spdp</AllowMulticast>

I also hardcoded the peer addresses for the Raspberry Pi and Create 3 robot interfaces. Some reading suggests usb0 interface cannot handle multicast properly.

Configuration on the Raspberry Pi

File located at

/home/rpi/systemd-services/testing-sleep-wake/cyclonedds.xml

We can reference this as follows in .bashrc:

source /opt/ros/humble/setup.bash
export RMW_IMPLEMENTATION=rmw_cyclonedds_cpp
export CYCLONEDDS_URI=/home/rpi/systemd-services/testing-sleep-wake/cyclonedds.xml
source ~/ros2_ws/install/setup.bash

Contents of the xml file are as follows:

<CycloneDDS>
  <Domain>
    <General>
      <AllowMulticast>spdp</AllowMulticast>
      <Interfaces>
        <NetworkInterface name="usb0" priority="10"/>
      </Interfaces>
    </General>
    <Discovery>
      <Peers>
        <Peer address="192.168.186.2"/>  <!-- Create 3 IP -->
      </Peers>
    </Discovery>
    <Tracing>
      <Verbosity>info</Verbosity>        <!-- Options: trace, debug, info, warning, error -->
      <OutputFile>/home/rpi/cyclonedds.log</OutputFile> <!-- Make sure the path is writable -->
    </Tracing>
  </Domain>
</CycloneDDS>
Configuration on the Create3 Robot

This configuration can be found in the beta features of the Create3 web interface:

<CycloneDDS>
  <Domain>
    <General>
      <AllowMulticast>spdp</AllowMulticast>
    <Interfaces>
      <NetworkInterface name="usb0" priority="10"/>
    </Interfaces>
    </General>
    <Discovery>
      <Peers>
        <Peer address="192.168.186.3"/>  <!-- RPi IP -->
      </Peers>
    </Discovery>
  </Domain>
</CycloneDDS>

usb0 interface

Was having trouble with the usb0 interface not activating on boot. Tried some different options in the connection profile, but in the end just made a quick systemd service to bring it up if it is down.

check-usb0.timer - this is the part you enable
[Unit]
Description=Run usb0 nmcli check every minute, starting 1 minute after boot

[Timer]
OnBootSec=60s
OnUnitActiveSec=60s
Persistent=true
Unit=check-usb0.service

[Install]
WantedBy=timers.target
check-usb0.service
[Unit]
Description=Check and bring up usb0 via nmcli if down
Wants=network.target

[Service]
Type=oneshot
ExecStart=/home/rpi/systemd-services/check-usb0.sh
check-usb0.sh - stored in /home/rpi/systemd-services
#!/bin/bash

# Set up logging
LOG_TAG="check-usb0"

# Check if usb0 connection exists
if nmcli connection show usb0 &>/dev/null; then
    echo "usb0 connection exists" | systemd-cat -t "$LOG_TAG"

    # Check if usb0 is connected
    if nmcli -t -f NAME,DEVICE connection show --active | grep -q '^usb0:'; then
        echo "usb0 is connected" | systemd-cat -t "$LOG_TAG"
    else
        echo "usb0 exists but is not connected. Attempting to bring it up..." | systemd-cat -t "$LOG_TAG"
        if nmcli connection up usb0; then
            echo "Successfully brought up usb0 connection" | systemd-cat -t "$LOG_TAG"
        else
            echo "Failed to bring up usb0 connection" | systemd-cat -t "$LOG_TAG"
        fi
    fi
else
    echo "usb0 connection does not exist" | systemd-cat -t "$LOG_TAG"
fi

Restarting Create3 application with API

The buttons in the WebServer don’t work due to a text alignment issue, but you can trigger an application restart from the Raspberry Pi like so:

curl -X POST http://192.168.186.2/api/restart-app

Should respond like so if successful, and the chime from the robot or WebServer logs show the restart:

{"status":"Restarting application."}

To-Do

When usb0 is down for too long, the create3 still has those strange multicasting errors. Need to try with Multicast set to false from the create3. <- That should not work.

Maybe can try with peers listed again, but I hate this. Can’t assume usb0 will always be up, create3 could bomb out with multicast at any time it seems.

Adding Desktop Ubuntu - working solution is with Zenoh

Changing the cyclonedds.xml on the rpi to include the following:

<NetworkInterface name="wlan0" priority="10"/>
<NetworkInterface name="wlx1cbfce2684be" priority="10"/>
<Peer address="192.168.0.75"/>   <!-- Ubuntu Desktop -->

I can communicate between the ubuntu desktop and Raspberry Pi, but no further. My next attempt is to install a DDS router: https://eprosima-dds-router.readthedocs.io/en/latest/rst/developer_manual/installation/sources/linux.html Failing this I will try setting static peer addresses, disabling multicast, and adding iptable rules on the raspberry pi.

Installing and building with colcon build at /home/rpi/DDS-Router. Seems to have built with colcon ok, so not is time to run.

Was able to ping the create3 from the ubuntu PC like so, by changing on the RPI:

sudo iptables -A FORWARD -o usb0 -i wlx1cbfce2684be -j ACCEPT
sudo iptables -A FORWARD -i usb0 -o wlx1cbfce2684be -j ACCEPT

and on the ubuntu PC, also change cyclonedds.xml:

sudo ip route add 192.168.186.2 via 192.168.0.197

You need to find a better way to diagnose these DDS issues.

Decisions

We are using cyclonedds because we get much better performance from Vizanti when using vizanti_rws.launch.py. cyclonedds works with this version of Vizanti, the fast DDS package is not available: rmw_fastrtps_dynamic_cpp. First: is rmw_fastrtps_dynamic_cpp truly not an option?

I simplified the cyclonedds.xml files removing a lot of Unicast parts and now we have:

  • Vizanti running again with TF fixed, we can see all the data.
  • So it is as before, however all the data that comes from the create 3 is not reachable from Ubuntu desktop.
  • Can see LiDAR and the base link -> laser transforms but these are generated on the rpi.

First try some tweaks with cyclonedds again, then could try the discovery server with FastDDS. could try spsd again.

Alternatively, try this zenoh bridge: https://github.com/eclipse-zenoh/zenoh-plugin-ros2dds

Zenoh

Going to use this between rpi and ubuntu desktop. It’s important to make sure that NO DDS communication can occur between 2 hosts that are bridged by zenoh-bridge-ros2dds. Otherwise, some duplicate or looping traffic can occur. The guide says preferably, enable MULTICAST on the loopback interface with this command (on Linux): sudo ip l set lo multicast on But I have not done so and it works. To make this permanent add this file: /etc/NetworkManager/dispatcher.d/10-enable-lo-mcast:

#!/bin/bash
if [ "$DEVICE_IFACE" = "lo" ] && [ "$2" = "up" ]; then
    /sbin/ip link set lo multicast on
fi

And make it executable.

Installing

To install Zenoh:

gpg --keyserver hkps://keyserver.ubuntu.com --recv-keys 829768EDD9BD8B8F
gpg --export 829768EDD9BD8B8F | gpg --dearmor | sudo tee /usr/share/keyrings/zenoh.gpg > /dev/null
gpg --no-default-keyring --keyring /usr/share/keyrings/zenoh.gpg --list-keys

Then create /etc/apt/sources.list.d/zenoh.list with following contents:

deb [signed-by=/usr/share/keyrings/zenoh.gpg] https://download.eclipse.org/zenoh/debian-repo/ /

Now you can do sudo apt update and install with:

sudo apt install zenoh-bridge-ros2dds

Running

To run, do this on the rpi:

zenoh-bridge-ros2dds

And on the Ubuntu machine:

zenoh-bridge-ros2dds -e tcp/192.168.0.197:7447
May 11, 2025 ∙