New RCLC parameter server features

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RCLC parameter server implementation has been refactored in version v3.0.8-rolling.

This upgrade has been implemented to add ROS 2 parameters features to the micro-ROS default user API, the RCLC.

As you know, micro-ROS supports a partial implementation of parameters in order to allow users to tailor the memory used by their embedded micro-ROS application. Sometimes, those kinds of optimizations make it necessary to cut off some interesting features.

During the lifetime of the first approach to the micro-ROS parameter server implementation available in micro-ROS Foxy and Galactic, the micro-ROS community has been providing feedback that have allowed us to prepare a major refactor for micro-ROS Rolling & Humble.

The new features are:

  • Removing parameters. Now micro-ROS parameters can be deleted via the common ros2 param delete.
  • Adding new undeclared parameters. By means of using ros2 param set on a non-existent parameter will create a new parameter if there is enough preallocated memory for it and allow_undeclared_parameters is enabled in configuration.
  • Parameter server on_change callback allows to reject parameter modification, creation or deletion.
    • Improved ros2 param describe integration with parameter description, constraints and read only support.
  • New extra low memory mode that allows an even lower memory footprint of the parameter server implementation at expense of disabling some features**

As a reference, a 7 parameter server with RCLC_PARAMETER_MAX_STRING_LENGTH = 50 and notify_changed_over_dds = true in an STM32F4 will take about 12 kB in normal mode and about 4 kB in the new extra low memory mode.

  • Take a look at an example of the new micro-ROS parameter server API.

  • Check the documentation related to the micro-ROS parameter server.

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Very nice.

Are there plans to support string parameters as well?

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We do not have plans for it due to issue with handling string length in the MCU static memory, but if you have any proposal please open a PR.

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Is there an issue tracking this? Perhaps also with details on what the problems/challenges are?

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No, feel free to open it in RCLC repo