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PX4 uORB Tunnel Bridge

Overview

The px4_uorb_tunnel bridge allows forwarding of internal PX4 uORB topics directly to ROS 2 over MAVLink. This is typically used for custom or high-bandwidth telemetry that does not map cleanly to standard MAVLink messages. In the SVEA architecture, this is specifically used to retrieve detailed rail-level telemetry from the custom SVEA power board (power_monitor topics).

Architecture

  1. PX4 firmware (Sender): The PX4_UORB_TUNNEL stream captures selected local uORB topics, serializes them (handling fragmentation if necessary), and sends them over MAVLink using the TUNNEL message (ID 128, payload type 0xE001).
  2. MAVROS (Transport): The standard mavros_node relays the raw MAVLink TUNNEL payload to ROS 2.
  3. SVEA Core Bridge (Receiver): The svea_core package provides a px4_uorb_tunnel node. It subscribes to the tunnel stream, decodes the custom binary payload, reconstructs fragmented messages, and republishes them as native ROS 2 topics under the /px4/uorb/* namespace.

Exposed ROS 2 Topics

When the tunnel bridge is active, you will see topics dynamically populate based on what the PX4 board is forwarding:

Raw Tunnel Interface

  • /px4/uorb_tunnel/frame: Raw extracted uORB frames decoded from the MAVLink tunnel (primarily for debugging).

Power Monitor Telemetry

The SVEA power board exposes multiple voltage and current sensors (INA226 and INA3221). These are surfaced in ROS 2 as:

  • /px4/uorb/power_monitor: Contains all power monitor updates multiplexed.
  • /px4/uorb/power_monitor/instance_X: Dedicated topics for each physical sensor/channel instance, guaranteeing isolation between rails.

Instance Determinism

The PX4 SVEA firmware guarantees deterministic ordering for the power monitor instances. For example, on the STM32F7 Clicker4: - instance_0 & instance_1: INA226 devices (e.g., ESC current shunt, Servo buck shunt). - instance_2 through instance_7: INA3221 channels (e.g., 5V/12V rails, auxiliary inputs).

Quick Start

1. Check PX4 Configuration

The board's startup script (rc.board_extras) usually configures this automatically. If you need to manually enable the PX4_UORB_TUNNEL stream from the PX4 NSH console: 

mavlink stream -u 0 -s PX4_UORB_TUNNEL -r 20

2. Run the ROS 2 Bridge

Assuming your MAVROS connection is already established (e.g., via the SVEA Docker compose setup):

ros2 run svea_core px4_uorb_tunnel

(Note: The SVEA Docker compose environment may already start this automatically in the background).

3. Verify Data

Use standard ROS 2 commands to verify that the tunnel is correctly decoding the uORB topics:

List the active topics: 

ros2 topic list | grep px4

Echo a specific power rail instance: 

ros2 topic echo /px4/uorb/power_monitor/instance_0

ros2 topic hz /px4/uorb/power_monitor/instance_0