Cannot listen for parameter changes

[rosterloh]

I've been trying to implement a ParameterEventHandler for a parameter provided by an mcu running micro-ROS as in this tutorial. Callbacks come in for 'normal' ros nodes but I don't ever get anything from micro-ROS. Is this expected?

System information:

• OS: Debian Bullseye
• ROS 2: Humble
• Version: main

[pablogs9]

Hello @rosterloh I will need some more details about your implementation, how are you creating the subscriber?

[rosterloh]

Hi @pablogs9, sorry I thought implementation was clear from the tutorial link

#include <memory>

#include "rclcpp/rclcpp.hpp"

class NodeWatchingParameters : public rclcpp::Node
{
public:
  NodeWatchingParameters()
  : Node("node_watching_parameters")
  {
    param_subscriber_ = std::make_shared<rclcpp::ParameterEventHandler>(this);

    auto cb = [this](const rclcpp::Parameter & p) {
      RCLCPP_INFO(
        this->get_logger(), "Received an update to parameter \"%s\" of type: %s: \"%.02lf\"",
        p.get_name().c_str(),
        p.get_type_name().c_str(),
        p.as_double());
    };
    auto remote_node_name = std::string("micro_ros_node");
    auto remote_param_name = std::string("a_double_param");
    cb_handle_ = param_subscriber_->add_parameter_callback(remote_param_name, cb, remote_node_name);
  }

private:
  std::shared_ptr<rclcpp::ParameterEventHandler> param_subscriber_;
  std::shared_ptr<rclcpp::ParameterCallbackHandle> cb_handle_;
};

int main(int argc, char ** argv)
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<NodeWatchingParameters>());
  rclcpp::shutdown();

  return 0;
}

[pablogs9]

Sorry for the confusion, I thought that you were subscribing in the micro-ROS side. In this case, the RCLC parameter library has an option for enabling the notifications: https://docs.vulcanexus.org/en/latest/rst/microros_documentation/user_api/user_api_parameter_server.html#options

[rosterloh]

Thank you @pablogs9 you were quite right. notify_changed_over_dds was set to false for me. I've changed this and added another publisher in micro_ros and now this works correctly.