The rclc parameter package

ROS 2 parameters allow the user to create variables on a node and manipulate/read them with different ROS 2 commands. Further information about ROS 2 parameters can be found here

This package provides the rclc API with parameter server instances with full ROS 2 parameter client compatibility. A parameter client has not been implemented for rclc (yet). Ready to use code examples related to this tutorial can be found in rclc/rclc_examples/src/example_parameter_server.c.

Table of contents

• Initialization
• Memory requirements
• Callback
• Add a parameter
• Delete a parameter
• Parameter description
• Cleaning up

Initialization

• Default initialization:

    // Parameter server object
    rclc_parameter_server_t param_server;
    // Initialize parameter server with default configuration
    rcl_ret_t rc = rclc_parameter_server_init_default(&param_server, &node);

    if (RCL_RET_OK != rc) {
      ... // Handle error
      return -1;
    }
    

• Custom options:

  The following options can be configured:

  • notify_changed_over_dds: Publish parameter events to other ROS 2 nodes as well.
  • max_params: Maximum number of parameters allowed on the rclc_parameter_server_t object.
  • allow_undeclared_parameters: Allows creation of parameters from external parameter clients. A new parameter will be created if a set operation is requested on a non-existing parameter.
  • low_mem_mode: Reduces the memory used by the parameter server, functionality constrains are applied.

    // Parameter server object
    rclc_parameter_server_t param_server;

    // Initialize parameter server options
    const rclc_parameter_options_t options = {
        .notify_changed_over_dds = true,
        .max_params = 4,
        .allow_undeclared_parameters = true,
        .low_mem_mode = false; };

    // Initialize parameter server with configured options
    rcl_ret_t rc = rclc_parameter_server_init_with_option(&param_server, &node, &options);
    if (RCL_RET_OK != rc) {
      ... // Handle error
      return -1;
    }
    

• Low memory mode:

  This mode ports the parameter functionality to memory constrained devices. The following constrains are applied:

  • Request size limited to one parameter on Set, Get, Get types and Describe services.
  • List parameter request has no prefixes enabled nor depth.
  • Parameter description strings not allowed, rclc_add_parameter_description is disabled.

  Memory benchmark results on STM32F4 for 7 parameters with RCLC_PARAMETER_MAX_STRING_LENGTH = 50 and notify_changed_over_dds = true:

  • Full mode: 11736 B
  • Low memory mode: 4160 B

Memory requirements

The parameter server uses five services and an optional publisher. These need to be taken into account on the rmw-microxrcedds package memory configuration:

# colcon.meta example with memory requirements to use a parameter server
{
    "names": {
        "rmw_microxrcedds": {
            "cmake-args": [
                "-DRMW_UXRCE_MAX_NODES=1",
                "-DRMW_UXRCE_MAX_PUBLISHERS=1",
                "-DRMW_UXRCE_MAX_SUBSCRIPTIONS=0",
                "-DRMW_UXRCE_MAX_SERVICES=5",
                "-DRMW_UXRCE_MAX_CLIENTS=0"
            ]
        }
    }
}

At runtime, the variable RCLC_EXECUTOR_PARAMETER_SERVER_HANDLES defines the necessary number of handles required by a parameter server for the rclc Executor:

// Executor init example with the minimum RCLC executor handles required
rclc_executor_t executor = rclc_executor_get_zero_initialized_executor();
rc = rclc_executor_init(
    &executor, &support.context,
    RCLC_EXECUTOR_PARAMETER_SERVER_HANDLES, &allocator);

File truncated at 100 lines see the full file

Changelog for package rclc_parameter

6.2.0 (2024-10-15)

• Use fully qualified node name in parameter events (#402)

6.1.0 (2023-06-15)

• Add empty set_atomically parameter service (#354)

3.0.9 (2023-03-22)

• Added documentation (#301)
• Fix parameter change event (#310) (#311)

3.0.8 (2022-04-14)

• Parameters fini memory (#253)
• Fix RCLC int parameter get (cherry-pick) (#272)
• rclc_parameter: Fix rcl return values (#270)
• Upgrade parameters (#274)

3.0.7 (2022-02-17)

• no changes

3.0.6 (2022-01-25)

• Add thread dependency to examples (Rolling) (#237) (resolves in this package only cpplint errors)

3.0.5 (2021-11-23)

• no change

3.0.4 (2021-11-17)

• Add rclc_parameter Quality Declaration (#144)
• Check all dynamic allocations in parameter server init (#169)

3.0.3 (2021-07-28)

• Version bump

3.0.2 (2021-07-26)

• Add test dependencies for rclc_parameter

3.0.1 (2021-07-17)

• Removed shared from rclc_parameter
• Ensure clean message when set_parameter
• Added QoS entity creation API
• Updated CMakeLists.txt
• Major vesion bump was neccessary because API change in rcl_lifecycle package

0.1.0 (2021-05-27)

• Initial release