micro-ROS Instructions (Ubuntu 24.04 LTS & ROS 2 Jazzy)

Experimental; not validated on MCU hardware. An MCU and a micro-ROS agent connection were unavailable for this release. Treat these source pointers and examples as a starting point to verify against your board, transport and Jazzy versions, not as proof that a firmware configuration works.

1. Architecture

micro-ROS connects constrained MCUs to the ROS 2 DDS graph via micro_ros_agent and rclc over Micro XRCE-DDS. RMW_UXRCE_ALLOW_DYNAMIC_ALLOCATIONS=OFF prevents dynamic growth of the RMW's static pools; it does not guarantee zero heap allocation throughout the firmware. See the Jazzy RMW configuration for the flag's scope.

2. Documentation Entry Points

For	Entry point
Tutorials, supported boards, transports	https://micro.ros.org/
Firmware build system (micro_ros_setup)	https://github.com/micro-ROS/micro_ros_setup
rclc executor / node API source	https://github.com/ros2/rclc

3. Key Concepts & Patterns

A. Embedded Client Node Setup (rclc in C)

#include <rcl/rcl.h>
#include <rclc/rclc.h>
#include <rclc/executor.h>
#include <std_msgs/msg/int32.h>

int main(void) {
  rcl_allocator_t allocator = rcl_get_default_allocator();
  rclc_support_t support = {0};
  rcl_node_t node = {0};
  rcl_publisher_t pub = {0};

  rclc_support_init(&support, 0, NULL, &allocator);
  rclc_node_init_default(&node, "mcu_node", "", &support);
  rclc_publisher_init_default(&pub, &node, ROSIDL_GET_MSG_TYPE_SUPPORT(std_msgs, msg, Int32), "chatter");

  // Clean up
  rcl_publisher_fini(&pub, &node);
  rcl_node_fini(&node);
  rclc_support_fini(&support);
  return 0;
}

B. Micro-ROS Agent Execution

# Serial Transport (e.g. UART to USB)
ros2 run micro_ros_agent micro_ros_agent serial --dev /dev/ttyUSB0 -b 115200

# UDP Transport
ros2 run micro_ros_agent micro_ros_agent udp4 --port 8888

4. Symptom -> Root Cause -> Action

Symptom	Likely root cause	Action
MCU node vanishes from graph after MCU reset, agent still running	XRCE session not re-created; firmware assumes a one-time init	Add a reconnect state machine: rmw_uros_ping_agent() periodically, re-init entities on failure
rclc_support_init returns error on the MCU	Transport not reachable (wrong serial dev/baud, UDP port/IP)	Run the agent with -v6 verbose and watch for session establishment; verify transport config in firmware
Publisher works but subscriber callback never fires	Executor never spun, or rclc_executor_init handle count smaller than the number of subscriptions/timers	Spin the executor in the main loop; count every subscription+timer+service in num_handles
Hard fault / crash when publishing string or sequence messages	Message memory not allocated — rclc doesn't auto-allocate unbounded fields	Allocate with micro_ros_utilities_create_message_memory or assign static buffers before publishing
Large messages never arrive	Payload exceeds XRCE-DDS stream/MTU buffer configured in the firmware	Increase the transport MTU/stream buffer in the colcon.meta / transport config, or shrink the message
Best-effort topics flood then stall on serial	Serial bandwidth saturated: publish rate x message size exceeds baud rate	Lower publish rate, raise baud rate, or switch to UDP transport