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Simple ROS 2 Subscriber in C++

A simple ROS 2 node which cyclically reads the CPU usage from the ctrlX Data Layer by reading the address framework/metrics/system/cpu-utilisation-percent and pushes on the ROS2 topic ros2_simple_talker_cpp. In the ctrlX Data Layer you can find any kind of information about the device, process, fieldbus and periphery. Please note, that this is a very basic example which uses the simplest method of reading in the ctrlX Data Layer. For improved performance and scalability you should consider creating a subscription instead of performing synchronuous (blocking) reads.

Prerequisites

  • ros-base snap. The base snap which provides the ROS 2 runtime binaries. Has to be installed on ctrlX OS. See ROS 2 Humble Base Snap.
  • An Ubuntu based build environment to build an app. See ctrlX Automation SDK.

Basis for this Project

This project is based on the official ROS 2 Tutorial: Writing a simple publisher and subscriber (C++).

Building a Snap

Building a snap has two steps:

  1. Colcon build: CMakeLists.txt defines how compile and link the C++ sources.
  2. snap build: snap/snapcraft.yaml defines how the compiled binaries are packed into the snap and how they are called on ctrlX OS.

Colcon Configuration

The colcon build tool is configured by CMakeLists.txt.

This section defines the ROS 2 packages needed:

find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)

And here the executables and their dependencies are defined:

add_executable(listener src/subscriber_member_function.cpp)
ament_target_dependencies(listener rclcpp std_msgs)

Snapcraft Configuration

snap/snapcraft.yaml defines how the snap will be build:

  • install/ is dumped into the snap
  • also wrapper/
  • Two apps (talker and listener) are copied into the snap and started as services
  • The snap - respectively the executables - uses the content interface of the ros-base snap (here the ROS 2 runtime is provided).

Build the Snap

Start this script:

./build-snap-amd64.sh

About

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https://www.boschrexroth.com/en/dc/imprint/

Licenses

SPDX-License-Identifier: Apache-2.0