Zenoh (PX4 ROS 2 rmw_zenoh)

main (planned for: PX4 v1.17) Experimental

Experimental

At the time of writing, PX4 Zenoh-pico is experimental, and hence subject to change.

PX4 supports Zenoh as an alternative mechanism (to DDS) for bridging uORB topics to ROS 2 (via the ROS 2 rmw_zenoh middleware). This allows uORB messages to be published and subscribed on a companion computer as though they were ROS 2 topics. It provides a fast and lightweight way to connect PX4 to ROS 2, making it easier for applications to access vehicle telemetry and send control commands.

The following guide describes the architecture and various options for setting up the Zenoh client and router. In particular, it covers the options that are most important to PX4 users exploring Zenoh as an alternative communication layer for ROS 2.

Architecture

The Zenoh-based middleware consists of a client running on PX4 and a Zenoh router running on the companion computer, with bi-directional data exchange between them over a UART, TCP, UDP, or multicast-UDP link. The router acts as a broker and discovery service, enabling PX4 to publish and subscribe to topics in the global Zenoh data space. This allows seamless integration with ROS 2 nodes using rmw_zenoh, and supports flexible deployment across distributed systems.

The client is the PX4 Zenoh-Pico Node referred to above, which is implemented in the PX4 zenoh module. This is based on Zenoh-Pico, a minimalistic version of Eclipse Zenoh (a data-centric protocol designed for real-time, distributed, and resource-constrained environments).

The router suggested above is zenohd.

INFO

UART is supported by Zenoh but has not yet implemented in the PX4 Zenoh-Pico node.

ROS 2 Zenoh Bring-up on Linux Companion

In order for PX4 uORB topics to be shared with ROS 2 applications, you will need the PX4 Zenoh-Pico Node client running on your FMU, connected to a Zenoh router running on the companion computer (or elsewhere in the network).

First select Zenoh as the ROS 2 transport by setting the RMW_IMPLEMENTATION environment variable as shown:

export RMW_IMPLEMENTATION=rmw_zenoh_cpp

Then start the Zenoh router using the command:

ros2 run rmw_zenoh_cpp rmw_zenohd

For more information about the Zenoh Router see the rmw_zenoh documentation.

PX4 Zenoh-Pico Node Setup

PX4 Firmware

Before setting up the Zenoh communication, first make sure that your firmware contains the driver that implements the zenoh driver, which provides the implementation of the PX4 Zenoh-Pico Node.

You can check if the module is present on your board by searching for the key CONFIG_MODULES_ZENOH=y in your board's default.px4board KConfig file. For example, you can see that the module is present in px4_fmu-v6xrt build targets from /boards/px4/fmu-v6xrt/default.px4board.

If CONFIG_MODULES_ZENOH=y is not preset you can add this key to your board configuration and rebuild. Note that due to flash constraints you may need to remove other components in order to include the module (such as the uxrce_dds_client module, which you will not need if you are using Zenoh).

The table below shows some of the PX4 targets that include Zenoh by default.

PX4 Target	Notes
px4_fmu-v6xrt	For FMUv6X-RT (reference platform for testing)
nxp_tropic-community
nxp_mr-tropic
nxp_mr-canhubk344
px4_sitl_zenoh	Zenoh-enabled simulation build
px4_fmu-v6x_zenoh	Zenoh-enabled firmware for FMUv6X

Zenoh is not included in the default px4_fmu- targets for any firmware other than px4_fmu-v6xrt (px4_sitl_zenoh and px4_fmu-v6x_zenoh are build variants).

TIP

You can check if Zenoh is present at runtime by using QGroundControl to find the parameter ZENOH_ENABLE. If present, the module is installed.

Enable Zenoh on PX4 Startup

Set the ZENOH_ENABLE parameter to 1 to enable Zenoh on PX4 startup.

Configure Zenoh Network

Set up PX4 to connect to the companion computer running zenohd.

PX4's default IP address of the Zenoh daemon host is 10.41.10.1. If you're using a different IP for the Zenoh daemon, run the following command (replacing the address) in a PX4 shell and then reboot:

zenoh config net client tcp/10.41.10.1:7447#iface=eth0

Note that for the simulation target with Zeroh (px4_sitl_zenoh) you won't need to make any changes because the default IP address of the Zenoh daemon is set to localhost.

WARNING

Any changes to the network configuration require a PX4 system reboot to take effect.

TIP

See PX4 Ethernet Setup for more information about Ethernet configuration.

PX4 Zenoh-pico Node configuration

The default configuration is auto-generated from the dds_topics.yaml file in the PX4 repository. This file specifies which uORB message definitions are to be published/subscribed by ROS 2 applications, and hence (indirectly) which topics are compiled into the zenoh module.

To inspect the current Zenoh configuration:

zenoh config

The PX4 Zenoh-pico node stores its configuration on the SD card under the zenoh folder. This folder contains three key files:

• net.txt – Defines the Zenoh network configuration.
• pub.csv – Maps uORB topics to ROS2 topics (used for publishing).
• sub.csv – Maps ROS2 topics to uORB topics (used for subscribing).

4. Modifying Topic Mappings

Zenoh topic mappings define how data flows between PX4's internal uORB topics and external ROS2 topics via Zenoh. These mappings are stored in pub.csv and sub.csv on the SD card, and can be modified at runtime using the zenoh config CLI tool.

WARNING

Any changes to the topic mappings require a PX4 system reboot to take effect.

There are two types of mappings you can modify:

• Publisher mappings: Forward data from a uORB topic to a Zenoh topic.
• Subscriber mappings: Receive data from a Zenoh topic and publish it to a uORB topic.

The main operations and their commands are:

• Publish a uORB topic to a Zenoh topic:

  zenoh config add publisher <zenoh_topic> <uorb_topic> [uorb_instance]

• Subscribe to a Zenoh topic and forward it to a uORB topic:

  zenoh config add subscriber <zenoh_topic> <uorb_topic> [uorb_instance]

• Remove existing mappings:

  zenoh config delete publisher <zenoh_topic>
  zenoh config delete subscriber <zenoh_topic>

After modifying the mappings, reboot PX4 to apply the changes. The updated configuration will be loaded from the SD card during startup.

Communicating with PX4 from ROS 2 via Zenoh

Once your PX4 FMU is publishing data into ROS 2, you can inspect the available topics and their contents using standard ROS 2 CLI tools:

ros2 topic list

Check topic type and publishers/subscribers:

ros2 topic info -v /fmu/out/vehicle_status
Type: px4_msgs/msg/VehicleStatus

Publisher count: 1

Node name: px4_aabbcc00000000000000000000000000
Node namespace: /
Topic type: px4_msgs/msg/VehicleStatus
Topic type hash: RIHS01_828bddbb7d4c2aa6ad93757955f6893be1ec5d8f11885ec7715bcdd76b5226c9
Endpoint type: PUBLISHER
GID: 82.99.74.2c.b6.7d.93.44.91.4d.fe.14.93.58.40.16
QoS profile:
  Reliability: RELIABLE
  History (Depth): KEEP_LAST (7)
  Durability: VOLATILE
  Lifespan: Infinite
  Deadline: Infinite
  Liveliness: AUTOMATIC
  Liveliness lease duration: Infinite

Subscription count: 0

PX4 ROS 2 Interface with Zenoh

The PX4 ROS 2 Interface Library works out of the box with Zenoh as a transport backend. This means you can publish and subscribe to PX4 topics over Zenoh without changing your ROS 2 nodes or dealing with DDS configuration. For setup details and supported message types, refer to the PX4 ROS 2 Interface Library.