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zenbedded_hardware_interface

A ros2_control SystemInterface implementation that communicates with microcontrollers via Zenoh. Reads sensor state from a Zenoh subscriber and writes joint commands to a Zenoh publisher.

Features

• Agent-less communication – no ROS 2 bridge process required on the MCU

• Lock-free state buffer using realtime_tools::RealtimeBuffer

• YAML-driven interface schema (via zenbedded_schema) for wire-format compatibility between host and firmware

• Configurable Zenoh endpoint, mode (client/peer), and topic keys

• Interfaces declared dynamically from the schema YAML

Parameters

The following parameters are read from the ros2_control URDF <param> tags:

Parameter	Type	Required	Default	Description
zenoh_endpoint	string	yes	–	Zenoh endpoint (e.g. tcp/127.0.0.1:7447)
state_topic	string	yes	–	Zenoh key expression for MCU state publications
command_topic	string	yes	–	Zenoh key expression for host command publications
schema_path	string	yes	–	Path to the interface schema YAML file
zenoh_mode	string	no	"client"	Zenoh session mode ("client" or "peer")

Example URDF snippet:

<ros2_control name="ZenbeddedSystem" type="system">
  <hardware>
    <plugin>zenbedded::ZenbeddedHardware</plugin>
    <param name="zenoh_endpoint">tcp/192.168.1.100:7447</param>
    <param name="zenoh_mode">client</param>
    <param name="state_topic">rt/robot/state</param>
    <param name="command_topic">rt/robot/command</param>
    <param name="schema_path">$(find zenbedded_hardware_interface)/config/interface_schema.yaml</param>
  </hardware>
  <joint name="motor_arm">
    <state_interface name="position"/>
    <command_interface name="position"/>
  </joint>
  <joint name="pendulum_axis">
    <state_interface name="position"/>
  </joint>
</ros2_control>

Example schema (config/interface_schema.yaml)

state_interfaces:
  motor_arm:
    position: float32
  pendulum_axis:
    position: float32
command_interfaces:
  motor_arm:
    position: float32

This generates the following packed C struct via zenbedded_schema:

typedef struct {
  float motor_arm_position;
  float pendulum_axis_position;
} zenbedded_state_t;

typedef struct {
  float motor_arm_position;
} zenbedded_command_t;

Lock-free state access

State updates from the Zenoh callback are written into a realtime_tools::RealtimeBuffer<std::vector<uint8_t>>, allowing the real-time control loop to read the latest state snapshot without blocking on the network callback.