RMW zenoh-pico implementation

Overview

The rmw_zenoh_pico is the implementation of the rmw layer with zenoh_pico. This package is generated using the Micro-ROS project stack.

This package provides the same future as the RMW Micro XRCE-DDS implementation.

This package is able to connect the rmw_zenoh layer, whose implementation is based on Zenoh and is written using the zenoh-c bindings by the ROS community.

Packages

What is rmw_zenoh_pico ?

• Implementation of the ROS 2 middleware abstraction interface written by C
• Generate micro-ROS applications using zenoh-pico
• A middleware implementation for zenoh-pico package
• Replacement XRCE-DDS on micro-ROS with zenoh-pico
• Wrapper of zenoh-pico API and zenoh-pico internal utilities(z_sting, z_mutex, etc.)
• The reference library implementation for the Zenoh protocol used from upper layers in the ROS 2 stack

Configuration

This package can be configured via CMake arguments.

Name	Description	Default	Config
RMW_ZENOH_PICO_TRANSPORT	Sets zenoh-pico transport to use (unicast, serial)	unicast	OK
RMW_ZENOH_PICO_TRANSPORT_MODE	Sets Zenoh transport connection mode	client	OK
RMW_ZENOH_PICO_CONNECT	Sets the scout address.	127.0.0.1	OK
RMW_ZENOH_PICO_CONNECT_PORT	Sets the scout port.	7447	OK
RMW_ZENOH_PICO_LISTEN	Sets the listen address.	127.0.0.1
RMW_ZENOH_PICO_LISTEN_PORT	Sets the listen port.	-1
RMW_ZENOH_PICO_SERIAL_DEVICE	Sets the agent serial port.	/dev/ttyAMA0	OK
RMW_ZENOH_PICO_SERIAL_DEVICE	Sets the agent serial port.*1	/dev/ttyAMA0	OK
RMW_ZENOH_PICO_MAX_LINENESS_LEN	This value sets the number of max liveliness resource length	256
RMW_ZENOH_PICO_C_STANDARD	Version of the C language used to build the library	99

*1 Will be supported in the future

Support rmw Functions

The rmw API for rmw_zenoh_pico is not currently as well supported as rmw_zenoh and rmw_microxrcedds_c. This list is support of rmw_zenoh_pico.

Important

The prototype implementation of rmw_zenoh_pico does not yet support graph information (gid).
Therefore, this implementation only supports pub/sub connections. Other connection types (server/client, node information, etc.) are not yet supported.

For rmw_zenoh_pico to support gid, several issues should be considered.
The rmw_zenoh_pico would like to support zenoh_pico and rmw_zenoh along with future updates from the ROS community.

Installing and build for rmw_zenoh_pico with the micro-ROS system

The rmw_zenoh_pico is used instead of the XRCE-DDS layer in the micro-ROS product.
The rmw_zenoh_pico has to install the micro-ROS product before building it.
For example, if you want to generate a host environment for rmw_zenoh_pico, please refer to the first_application_linux document to install the host environment.

Table: Related repositories

Repository	Branch	SID	URL
micro_ros_setup	jazzy	9ae1ca79ca3cb5f8fbd3867d02a6e43686388f05	https://github.com/micro-ROS/micro_ros_setup
zenoh-c	release/0.11.0	c8f6ca07f77d684a0ce4a8b31eae4c4a11c9bb58	https://github.com/eclipse-zenoh/zenoh-c.git
zenoh-pico	release/0.11.0	a3ab7f79617c0076693852e68e75a50053463ae4	https://github.com/eclipse-zenoh/zenoh-pico.git
rmw_zenoh	rolling	011cc79f564f7f4ab0e47e1604062c14c355546a	https://github.com/ros2/rmw_zenoh.git
zenoh	main	2500e5a62d8940cbfbc36f27c07360f91ba28c2d	https://github.com/eclipse-zenoh/zenoh.git

Create a workspace and download the micro-ROS tools

unset RMW_IMPLEMENTATION 
mkdir uros_ws && cd uros_ws
git clone -b rmw_zenoh_pico https://github.com/esol-community/micro_ros_setup src/micro_ros_setup
rosdep update && rosdep install --from-paths src --ignore-src -y
colcon build

Note

1. The rmw_zenoh_pico need part of any library which is used by get hash value in the fastdds library. Therefore, the value of RMW_IMPLEMENTATION should not be set before building rmw_zenoh_pico if you use customize rmw_middleware (ex. cyclonedds).
2. The rmw_zenoh_pico have to add patch to product of micro_ros_setup. If you need the patched product, you can clone the branch of rmw_zenoh_pico from mirror of micro_ros_setup.

Creating a new firmware workspace

The rmw_zenoh_pico has demo programs.
This section introduces a sample communication example between rmw_zenoh_pico and zenoh_pico.

Target connection summary:

Target environments:

Target	IP address
Linux target (local connect) / zenohd	localhost
Linux target (external connection) / zenohd	10.0.30.10
Raspberry-pi target	10.0.30.50

Type of rmw	ROS application name	Node name
rmw_zenoh	talker	/talker
rmw_zenoh_pico	listener	/listener_node

use token
/chatter

Build Linux target

# cd uros_ws
source install/local_setup.bash
ros2 run micro_ros_setup create_firmware_ws.sh zenoh host
source install/local_setup.bash
ros2 run micro_ros_setup build_firmware.sh
file ./install/rmw_zenoh_pico/lib/rmw_zenoh_demos_rclc/listener/listener
# ./install/rmw_zenoh_pico/lib/rmw_zenoh_demos_rclc/listener/listener: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=2c0119cf4620f58fafa736594d3bba038e56e13a, for GNU/Linux 3.2.0, not stripped

Build Raspberry Pi target

# cd uros_ws
source install/local_setup.bash
ros2 run micro_ros_setup create_firmware_ws.sh zenoh raspbian bookworm_v12
ros2 run micro_ros_setup configure_firmware.sh listener -t unicast -i <zenohd ip> -p <zenohd port>
source install/local_setup.bash
ros2 run micro_ros_setup build_firmware.sh
file ./firmware/bin/listener
# ./firmware/bin/listener: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, with debug_info, not stripped

The zenoh_pico in rmw_zenoh_pico is executing in client mode, and the connection has to be set to zenoh/zenohd.
The Raspberry Pi OS configuration for rmw_zenoh_pico has to set their IP address and port when executing configure_firmware.

Name	Mean	Example
zenoh ip	address connect zenoh/zenohd	-i 10.0.30.10
zenoh port	port connect zenoh	-p 7447

The Raspberry Pi OS configuration on this patch on the rmw_zeno_pico package used Raspberry Pi 1 and Raspberry Pi Pico toolchains (ELF32bit/EABI5).
If you want to use another Raspberry Pi target, which is a 64-bit environment, you have to change part of the toolchain URL in create.sh manually.

$ cat micro_ros_setup/config/zenoh/raspbian/create.sh 
#! /bin/bash

pushd $FW_TARGETDIR/$DEV_WS_DIR >/dev/null
    if [ $OPTION == "bookworm_v12" ]; then
        TOOLCHAIN_URL="https://..."              /* Change URL of cross-compile toolchain */
                                                 /* For match target Raspberry Pi OS environment */
    else
        echo "Platform not supported."
        exit 1
    fi
       :

See: https://sourceforge.net/projects/raspberry-pi-cross-compilers/files/Raspberry%20Pi%20GCC%20Cross-Compiler%20Toolchains/

Build RTOS target

T.D.B

Running the micro-ROS app

For sample details, see Setup and Test in the rmw_zenoh repository.

Running common service on Linux

The following commands are executed on another terminal, respectively.

1. Start the Zenoh router on rmw_zenoh

   # cd <directory in install rmw_zenoh> 
   source install/setup.bash
   ros2 run rmw_zenoh_cpp rmw_zenohd

2. Run the talker on rmw_zenoh

   # cd <directory in install rmw_zenoh> 
   sudo apt-get install ros-$ROS_DISTRO-demo-nodes-py
   sudo apt-get install ros-$ROS_DISTRO-demo-nodes-cpp
   source /opt/ros/$ROS_DISTRO/local_setup.bash
   source install/setup.bash
   export RMW_IMPLEMENTATION=rmw_zenoh_cpp
   ros2 run demo_nodes_cpp talker

Running Linux target

1. Run the listener on rmw_zenoh_pico in microros

   # cd uros_ws
   source install/local_setup.bash
   export RMW_IMPLEMENTATION=rmw_zenoh_pico
   ros2 run rmw_zenoh_demos_rclc listener

Running Raspberry Pi target (on Raspberry Pi H/W)

1. Copy the micro-ROS application to Raspberry Pi

   # cd uros_ws
   scp firmware/bin/listener <target raspberry pi>:~/.

2. Listen application

   ssh <target raspberry pi>
   ./listener

Running RTOS target

T.D.B

Name of node/topic on ROS 2 (option)

The ROS 2 CLI command starts a new ROS 2 daemon task, and the daemon caches data.
If the ROS 2 daemon is already running, it must be stopped before executing ROS 2 CLI commands.

1. Get the node name if the listener node is executed

   ros2 daemon stop
   # The daemon has been stopped
   source install/setup.bash
   export RMW_IMPLEMENTATION=rmw_zenoh_cpp
   ros2 node list
   # [INFO] [1728446929.812251213] [rmw_zenoh_cpp]: Successfully connected to a Zenoh router with id aebe653d2ff57b4ba1ef7b43c59b547.
   # [WARN] [1728446931.353213030] [rmw_zenoh_cpp]: Received liveliness token to remove node /_ros2cli_361692 from the graph before all pub/subs/clients/services for this node have been removed. Removing all entities first...
   # /listener_node

2. Get the topic name if the listener node is executed

   ros2 daemon stop
   # The daemon has been stopped
   source install/setup.bash
   export RMW_IMPLEMENTATION=rmw_zenoh_cpp
   ros2 topic list
   # [INFO] [1728446957.797293950] [rmw_zenoh_cpp]: Successfully connected to a Zenoh router with id aebe653d2ff57b4ba1ef7b43c59b547.
   # [WARN] [1728446959.338124246] [rmw_zenoh_cpp]: Received liveliness token to remove node /_ros2cli_361735 from the graph before all pub/subs/clients/services for this node have been removed. Removing all entities first...
   # /parameter_events
   # /rosout
   # /chatter

The new ROS 2 daemon started by ROS 2 CLI exits when this command exits.
At this time, the rmw_zenoh middleware outputs a few messages. This message will change depending on your build/execute environment.

Purpose of the Project

This software is not ready for production use. It has neither been developed nor tested for a specific use case.
However, the license conditions of the applicable open-source licenses allow you to adapt the software to your needs. Before using it in a safety-relevant setting, ensure the software fulfills your requirements and adjusts them according to applicable safety standards, e.g., ISO 26262.

License

This repository is open-sourced under the Apache-2.0 license. See the LICENSE file for details.

For a list of other open-source components included in this repository, see the file 3rd-party-licenses.txt.

Known Issues/Limitations

1. The pub/sub message from rmw_zenoh_pico does not use attempt data.
   The rmw_zenoh is using Zenoh package, and the message from rmw_zenoh append additional data on future attempts with Zenoh.
   The additional data on rmw_zenoh is "gid", "sequence_number" and "source_timestamp".
   The rmw_zenoh_pico is using zenoh pico package. However, the rmw_zenoh_pico with zenoh-pico cannot exchange the attempt data.
   Therefore, rmw_zenoh_pico does not yet support the full RMW API except for working communication between subscribers and publishers.

2. How to share liveliness information data.
   The rmw_zenoh pico can use some ROS 2 CLI commands. However, this implementation is provisional.
   The rmw_zenoh is controlled by liveliness information, which generates keyexpr data by z_declare_keyexpr(). And their information saves resource data in each internal memory.
   The rmw_zenoh is executed in the Zenoh P2P mode. This P2P mode can be exchanged when a Zenoh peer connects to another peer.
   Conversely, rmw_zenoh_pico connects to the Zenoh network in client mode. The zenohd does not forward keyexpr data. In client mode, there is no way to exchange internal resource keyexpr data with other peers because no P2P connection is performed.
   Currently, the rmw_zenoh_pico works around this problem by creating a new subscribe key for liveliness information. This new subscribe key is used only in the future.
   We feel that this implementation is not very suitable for poor MPCs and upper-layer applications. And if we find a more effective way to approach this issue, we will need to change this implementation.

3. The rmw_zenoh_pico using malloc() system futures when there is a new memory region.
   The XRCE-DDS implementation has simple memory futures in its layer. This memory future is designed to run ROS 2 communication for small resource systems.
   The rmw_zenoh layer can execute on a Linux system with a memory subsystem for a large system with Zenoh.
   The zenoh-pico is designed for small resource systems.
   However, the zenoh-pico memory is compiling into its system, and it is not designed to use the same data area with an upside layer, which is rmw_zenoh_pico.
   If you use rmw_zeno_pico on a small resource system with any RTOS, you might need to add some customizations for zenoh-pico and rmw_zenoh_pico.