README

General information about this repository, including legal information, build instructions and known issues/limitations, are given in README.md in the repository root.

The rclc_examples package

The rclc_examples package provides examples for using the RCLC-Exector and convenience functions for creating RCL objects like subscriptions and timers.

Table of contents

Minimal publisher-subscriber

The example example_executor.c demonstrates basic features of the rclc package and the rclc-Executor to setup a publisher and a subscriber. This example uses also the convenience functions to configure rcl objects, like subscriptions, timers, etc. This saves in this case about 24% of lines of code compared the the same application with direct rcl-API, as described in the setup Minimal publisher-subscriber only with RCL-API.

Step 1 Setup ROS 2 Workspace

Open a terminal with ROS 2 workspace. Assuming that the ROS 2 installation resides in /opt/ros/ROSDISTRO, setup the ROS2 environment by:

~$ source /opt/ros/ROSDISTRO/setup.bash

Step 2 Build the package Download and build the rclc repository in a workspace (for example ros2_ws). Then source the workspace:

~/ros2_ws/$ colcon build --packages-up-to rclc_examples
~/ros2_ws/$ source ./install/local_setup.bash

Step 3 Run the example executor demo.

The binary of the example is example_executor.

~/ros2_ws/$ ros2 run rclc_examples example_executor

Example output:

Created timer with timeout 1000 ms.
Created subscriber topic_0:
Debug: number of DDS handles: 2
Published message Hello World!
Callback: I heard: Hello World!
Published message Hello World!
Callback: I heard: Hello World!
Published message Hello World!
Callback: I heard: Hello World!
Published message Hello World!
Callback: I heard: Hello World!
Published message Hello World!
Callback: I heard: Hello World!

Minimal publisher-subscriber only with RCL-API

Step 1 Setup ROS 2 Workspace

Open a terminal with ROS 2 workspace. Assuming that the ROS 2 installation resides in /opt/ros/ROSDISTRO, setup the ROS2 environment by:

~$ source /opt/ros/ROSDISTRO/setup.bash

Step 2 Build the package Download the rclc repository in a workspace (for example ros2_ws). Then source the workspace:

~/ros2_ws/$ colcon build --packages-up-to rclc_examples
~/ros2_ws/$ source ./install/local_setup.bash

It should build these packages:

  • rcl_yaml_param_parser

  • rcl

  • rclc

  • rclc_examples

Step 3 Run the example executor.

The binary of the example is example_executor_only_rcl.

~/ros2_ws/$ ros2 run rclc_examples example_executor_only_rcl

The publisher publishes the message Hello World!in topic_0 at a rate of 1Hz and the subscriber prints out in the callback Callback: I heard: Hello World!.

You should see the following output:

Created timer with timeout 1000 ms.
Created subscriber topic_0:
Debug: number of DDS handles: 2
Published message Hello World!
Callback: I heard: Hello World!
Published message Hello World!
Callback: I heard: Hello World!
Published message Hello World!
Callback: I heard: Hello World!
Published message Hello World!
Callback: I heard: Hello World!
Published message Hello World!
Callback: I heard: Hello World!

RCLC-Executor with trigger function

example_executor_trigger.c demonstrates the rclc-Executor with a trigger function.

Step 1, Step 2 To setup ROS2 workspace and build the package refer to Step 1 and Step 2 in the Minimal publisher-subscriber.

Step 3 This example implements two RCLC Executors, one for publishing executor_puband one for subscribing messages executor_sub.

The Executor executor_pub publishes string topic_0 every 100ms (using a timer with 100ms) and an integer topic_1 every 1000ms (using a timer with 1000ms).

With the trigger condition rclc_executor_trigger_any this executor publishes whenenver any timer is ready.

Executor executor_sub has two subscriptions, my_string_sub and my_int_sub subscribing to topic_0 and topic_1, respectivly.

With the trigger condition rclc_executor_trigger_all this executor starts evaluating the callbacks only when both messages have arrived. To make this clearly visible, we set the quality of service parameter of the length of the DDS-queue to 0 for subscription my_string_sub, which subscribes to topic_0 with the higher rate.

my_subscription_options.qos.depth = 0
rc = rcl_subscription_init(
  &my_string_sub,
  &my_node,
  my_type_support,
  topic_name,
  &my_subscription_options);

Consequently, the messages “in between” are lost.

The binary of the example is example_executor_trigger. You run the example with:

~/ros2_ws/$ ros2 run rclc_examples  example_executor_trigger

Then you should see the following output:

Created timer 'my_string_timer' with timeout 100 ms.
Created 'my_int_timer' with timeout 1000 ms.
Created subscriber topic_0:
Created subscriber topic_1:
Executor_pub: number of DDS handles: 2
Executor_sub: number of DDS handles: 2
Published: Hello World! 0
Published: Hello World! 1
Published: Hello World! 2
Published: Hello World! 3
Published: Hello World! 4
Published: Hello World! 5
Published: Hello World! 6
Published: Hello World! 7
Published: Hello World! 8
Published: Hello World! 9
Published: 0
Callback 1: Hello World! 9  <---
Callback 2: 0               <---
Published: Hello World! 10
Published: Hello World! 11
Published: Hello World! 12
Published: Hello World! 13
Published: Hello World! 14
Published: Hello World! 15
Published: Hello World! 16
Published: Hello World! 17
Published: Hello World! 18
Published: Hello World! 19
Published: 1
Callback 1: Hello World! 19 <---
Callback 2: 1               <---

The results show, that the callbacks are triggered together, only when the integer message topic_1 was published and received. At that moment the current string message of the topic_0 is processed as well.

Service and client node

The two files example_service_node.c and example_client_node.c demonstrate service/client functionality in micro-ROS.

Step 1, Step 2 To setup ROS2 workspace and build the package refer to Step 1 and Step 2 in the Minimal publisher-subscriber.

Step 3 Open two Terminal windows and source the ROS 2 distribution/install/setup.bash and rclc repository/install/local_setup.bash.

window 1: start service node

$ ros2 run rclc_examples example_service_node
INFO: rcl_wait timeout 10 ms
Service request value: 24 + 42. Seq 1
Received service response 24 + 42 = 66. Seq 1

window 2: start client node

~$ ros2 run rclc_examples example_client_node
Send service request 24 + 42. Seq 1
INFO: rcl_wait timeout 10 ms

A request message is sent from the client node to the service node and answered.

Action server and client

The files example_action_client.c and example_action_server.c demonstrate the action client and action server functionality in micro-ROS.

Lifecycle node

The file example_lifecycle_node.c demonstrates the lifecycle node functionality in micro-ROS.

Parameter server

The file example_parameter_server.c demonstrates the parameter server functionality in micro-ROS.

Subscription callback with C++ class method

The files example_pingpong.cpp, example_pingpong_helper.h, example_pingpong_helper.c implement a ping-pong demo using a method of a C++ class as subscription callback.

Subscription with context

The file example_sub_context.c shows, how to use a subscription with a context. This allows the subscription to access some other data structure additionally to the message data.

Real-time concurrency with slow timer and long subscription

The example example_short_timer_long_subscription.c demonstrates what happens, if a high frequency timer (every 100ms) and a subscription with a long processing time is managed by one executor. This demo shows, that the timer events are dropped during the long processing time of the subscription and are also not caught-up when there would be sufficient time.