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Component-based software architectures in robotics

Robots are highly complex systems that embed numerous sensors and actuators, in the service of a variety of algorithms performing heterogeneous tasks. They often have to deal with severe requirements (timing constraints, limited energy, memory and processing resources, etc.) and must show a robust conception as uncertainty about their environment is high, and unexpected events can have critical consequences.

To facilitate the development of robotic software, component-based architectures, where components are independent processes, have become the de facto standard in robotics. Each software component is dedicated to a given task, from low-level control to high-level processing. Components communicate with each other with the help of a software piece called the middleware.

For instance, consider a robot embedding a camera and performing object detection in the images. One component could be in charge of acquiring the images using the camera’s driver, and would output them. Another component could input the images and run an algorithm on them to detect objects, producing the detection result as output for any other component in need of this information. Routing data from the output of the first component to the input of the second one is ensured by the middleware, this is called data flow.

Components offer services to the user to modify their behaviour and adapt to different situations. To follow with the example above, the component acquiring images could provide a service to select which camera to use, another one to configure parameters such as the image size and the number of frames per second, a third one to explicitly request the start of the acquisition, etc. The component detecting objects could have a service to change some parameters in the detection algorithm, another one to choose which image stream to take as input (because there could be several components streaming images from different cameras), etc. Making services available to the user is again handled by the middleware, this is called control flow.


The user mentioned here is not necessarily a physical person. For autonomous robots, it will probably be a detached software piece, supervising the state of the robot and choosing to start a given service to accomplish a new goal. This software piece belongs to the decisional level, while other components make up the functional level.

Component-based software architectures offer great benefits in robotics, in particular [1]:

  • Modularity
    • As many operations handled by a robot require to have their own thread of execution (e.g. data acquisition for sensors, motion control for actuators), having them in separate programs eases their concurrent execution.
    • The architecture can be adapted to the needs of the robot: adding a new hardware piece such as a sensor will result in running a new software component to drive it.
    • The system can be distributed over a network, as the middleware seamlessly ensures communication between components running on different host machines.
  • Re-usability
    • Common components can be used across robots without having to recode them from scratch.
    • Components can be packaged and easily shared in the robotics community, where open source software prevails.
    • Re-usable components reduce development cost and time, while improving software quality and sustainability.

ROS, a software platform for robotics

The previous section identifies the middleware as the software piece ensuring data flow between functional components, and allowing their control.

ROS is a widely known software platform in robotics, providing not only a middleware, but also implementing a wide range of commonly-used functionalities into software components (such as localisation, mapping, path-planning, obstacle avoidance, etc.), with a build system and a packaging system for easy compilation and installation. ROS benefits from a large community of users and developers, and runs on many robots today. This makes ROS a common choice as a robotic software platform, as it is for Two!Ears.

ROS embraces the principles of component-based software architectures, allowing distributed computation, software reuse and rapid testing [2]. If you will be a user of a robotic platform running ROS, the core tutorials can help you to get familiar with the ROS environment. The main ROS terminology, introduced in the tutorials, is recalled here:

Software components using ROS middleware are called ROS nodes.
Topics and messages
Data flows are called topics. A node that outputs data publishes on a topic. A node that inputs data subscribes to a topic. The data elements flowing on topics are called messages. Each message is made of various data fields forming part of a data structure called message type. As a given topic only carries one message type, the term topic type is equally used.
Services and actions
Nodes can provide services to control them. Some special services that can take a long time to execute are called actions.


In spite of its name, ROS does not replace, but instead works alongside a traditional operating system. As it provides features such as hardware abstraction and low-level device control [3], ROS has some similarities with an OS (Operating System), hence its name.

GenoM3, a tool to develop robotic components

The process of developing robotic components can significantly be improved by the mean of a tool called GenoM3. As a result of two decades of research on real time architectures for autonomous systems [4] [5], GenoM3 brings valuable attributes to robotic components:

  • Middleware independence

    Components developed with GenoM3 are middleware independent, i.e. they are not tied to a specific middleware and can be compiled for different middlewares without changing their source code.

    This is achieved through the notion of templates: a GenoM3 template is a set of instructions which, when applied to the component’s source files, automatically generates the code related to middleware communication. A clear separation of concerns between the algorithmic core and the middleware is thus conducted, helping towards the good design of robotic components.

    ROS appears among the middlewares supported by GenoM3. When using ROS templates to compile a GenoM3 component, the resulting program is a genuine ROS node. Only the development process differs from what could be done by writing a ROS node without the GenoM3 tool.

  • Model-driven design

    GenoM3 emphasises the clear definition of robotic components by adopting a model-driven approach. A GenoM3 component is first defined by a description file, called the dotgen file, with the .gen extension. This file gathers in a single place all the definitions related to the component’s interface, needed by a user to interact with it.

    Each GenoM3 component has its own dotgen file, mainly including the definition of its services and its data flows by the mean of ports (either from the component to the outside, or the other way round). Each service is defined by a name and a list of input and output parameters with their related data type. Each port is defined by a name, a direction (either in or out), and a data type for the data elements it uses. The dotgen file often include in-line documentation to help the understanding of the component’s features (for instance, the role of a given service parameter).

    On the basis of the model specified in the dotgen file, GenoM3 automatically generates real time code as well as skeletons of functions run by the services. So, the developer just has to fill these functions, called codels (for code element) with its algorithms. The corresponding algorithmic core is written in separate C or C++ source files or libraries.

  • Powerful framework

    GenoM3 facilitates the development of essential features for robotic components, such as:

    • the definition of finite state automata with an optional clock,
    • clean interruption mechanisms,
    • efficient error handling.

If you decide to be a user of GenoM3 components, the tutorial GenoM3 through an example will help you to learn how to read dotgen files. For a developer of GenoM3 components, the documentation defines the whole grammar for writing dotgen files, and how dotgen specifications are mapped into C or C++ codels.


GenoM3 components are often called modules (hence the name Generator of Modules). The words module and component refer to the same entity: an independent program that can run on a host machine where the robotic software architecture is distributed.

[1]A. Brooks, T. Kaupp, A. Makarenko, S. Williams, and A. Ore- back. Towards component-based robotics. In IEEE International Conference on Intelligent Robots and Systems, pages 163–168, Tsukuba (Japan), 2005.
[2]Jason M. O’Kane. A Gentle Introduction to ROS., 2014.
[4]R. Alami, R. Chatila, S. Fleury, M. Ghallab, and F. Ingrand. An Architecture for Autonomy. In Int. Jour. on Robotics Research 17, pages 315–337, 1998.
[5]A. Mallet, C. Pasteur, M. Herrb, S. Lemaignan, and F. Ingrand. GenoM3: Building Middleware-independent Robotic Components. In IEEE Int. Conf. on Robotics and Automation, Anchorage (Alaska), 2010.

Installation of the robotic tools

The robotic tools should be installed on any system that hosts components of the software architecture for the Robotic platform. This section details the installation process.


For all the guidelines gathered here, we will assume that you are using Ubuntu GNU/Linux as it is the supported distribution for ROS (though any other UNIX platform should be suited to the GenoM3 tools). Many commands given here are intended for the bash shell. If you use a different shell, you should adapt the bash-related commands accordingly.

Install ROS

The ROS distribution you can install will depend on your Ubuntu version:

Install the GenoM3 tools through robotpkg

This section will guide you through the installation of the GenoM3 tools. GenoM3 is open-source software (available at and can be compiled from source, but the common installation uses robotpkg, a compilation framework and packaging system for robotics software (more information at

Get robotpkg on your system


The following instructions invite you to download two git repositories. If the given URLs using git:// protocol fail, try https:// protocol as instructed here and there. If you need an introduction to git have a look at Git for beginners.

First, get the robotpkg repository in your home folder (you can choose another location, but we recommend this one):

git clone git://

You will also need the wip subset of robotpkg, it contains some work in progress that is not officially released, but already available:

cd ~/robotpkg
git clone git:// wip

Next, set the installation path. The tools that you will soon install will be placed in your home folder under a dedicated folder named openrobots. Installing robotic components in your home folder ensures that you do not need root privileges for the installation (you can choose another location with a different prefix, but we recommend this one):

cd ~/robotpkg/bootstrap
./bootstrap --prefix $HOME/openrobots

To finish, update your environment variables to include the installation folder:


In the following commands, note the use of an environment variable ROBOTPKG_BASE to indicate your installation path, set to $HOME/openrobots. If you have selected a different location at the previous step, you should modify the corresponding command accordingly.

echo >> ~/.bashrc
echo '# ROBOTPKG' >> ~/.bashrc
echo 'export ROBOTPKG_BASE=$HOME/openrobots' >> ~/.bashrc
echo 'export PATH=$PATH:$ROBOTPKG_BASE/bin:$ROBOTPKG_BASE/sbin' \
     >> ~/.bashrc
     $ROBOTPKG_BASE/lib/pkgconfig' >> ~/.bashrc
     $ROBOTPKG_BASE/src/ros-nodes:$ROBOTPKG_BASE/share' >> ~/.bashrc
     $ROBOTPKG_BASE/lib/python3.2/site-packages' >> ~/.bashrc
echo '# ROBOTPKG END' >> ~/.bashrc
source ~/.bashrc

How to install a robotpkg package

Your ~/robotpkg directory contains a tree of packages, grouped into main categories. In the next part, we will invite you to install some of those packages. Here, we expose you the guidelines to follow for each package.

  1. Add options to the package

    If you are asked to add options option-1 option-2 ... to the package pkg-name, edit the file ~/openrobots/etc/robotpkg.conf and add a line (near the beginning for instance) looking like:

    PKG_OPTIONS.pkg-name+= option-1 option-2 ...

    You will get a better idea about this step with an actual example in the next part.

  2. Move to the package’s directory

    You will be given the path to the package, such as robotpkg/category/pkg-name. Change to this directory:

    cd ~/robotpkg/category/pkg-name
  3. Install possibly missing system dependencies

    Run the following command to list the dependencies for the package you are about to install:

    make show-depends

    At the end of the command’s output, the dependencies are separated into Robotpkg dependencies and System dependencies. If any robotpkg dependency is missing, it will be automatically installed. If any system dependency is missing, you need to install it (commonly with apt-get under Ubuntu). Iterate this step until no system dependency is missing.

    You may skip this step, but if a system dependency is missing, the package installation will stop at some point and you will be asked to install it.

  4. Install the package

    Run the following command:

    make update

    This will download the sources, compile them locally on your system, and install the output files in the ~/openrobots directory.

Install packages for GenoM3

  • Install the package demo-genom3 from robotpkg/doc/demo-genom3 with options codels ros-server ros-client-ros ros-client-c.

    This package will install the demo component. It is a sample component distributed with GenoM3, serving as an example, simply controlling the motion of a fictional robot. The aim of installing the demo component is twofold: first, it automatically installs all the dependencies for using GenoM3 (the provided options specifying that we will use the ROS templates); second, you get a GenoM3 component ready to be run to start using the robotic tools.

    For your convenience, here is how applying the above steps could look like:

    # 1. Add options to the package
    echo 'PKG_OPTIONS.demo-genom3+= codels ros-server ros-client-ros ros-client-c'\
          >> ~/openrobots/etc/robotpkg.conf
    # or better, edit the file manually and add the line near the beginning
    # 2. Change to the package's directory
    cd ~/robotpkg/wip/demo-genom3
    # 3. Install missing system dependencies
    make show-depends
    # Let's say that `make show-depends` revealed two missing system
    # dependencies named 'bison' and 'flex'. Next step would be:
    sudo apt-get install bison flex
    make show-depends
    # No missing system dependency left
    # 4. Install the package
    make update
  • Then, install the packages genomix from robotpkg/net/genomix and rosix from robotpkg/net/rosix.

    genomix and rosix are HTTP servers providing an interface for some clients to control GenoM3 components and generic ROS nodes respectively.

  • Then, install the packages tcl-genomix from robotpkg/wip/tcl-genomix and matlab-genomix from robotpkg/supervision/matlab-genomix.

    These are clients of genomix and rosix servers. The tcl-genomix client allows to control components using the Tcl language. Its installation is not mandatory (we will rather use the matlab-genomix client), but recommended as a common package distributed with GenoM3. The matlab-genomix client allows to control components from Matlab.


    You need a Matlab installation on your system in order to install the matlab-genomix package. If you encounter a missing dependency for mex (the MEX compiler from Matlab), you need to add the path to Matlab executables to the PATH environment variable. For example, with Matlab R2013a installed in /usr/local/MATLAB/R2013a, it would be done with:

    export PATH=$PATH:/usr/local/MATLAB/R2013a/bin

The GenoM3 tools are now installed on your system. If you want to try the Matlab bridge, you can follow the official tutorial using the demo component. You can also follow the instructions below to install BASS, an audio streaming server component and later on follow the tutorial Stream binaural signals from BASS to Matlab.


The Matlab bridge is installed in ~/openrobots/lib/matlab. To follow the tutorials using matlab-genomix, you need to add this path to the Matlab path.

Install a GenoM3 component from the sources


The software part of the Two!Ears robotic architecture includes several GenoM3 components. You may have to install them from their source files. Each GenoM3 component has its own folder, containing a description file named after the component with the .gen extension (something like component.gen). These steps will install the component in your ~/openrobots folder:

cd path/to/component/folder
genom3 skeleton -i component.gen
mkdir build && cd build
../configure --prefix=$ROBOTPKG_BASE --with-templates=ros/server,ros/client/c
make install

Example: installing the BASS component

BASS is a component for binaural audio streaming. The folder for this component is named bass-genom3, under the RoboticPlateform folder of the software repository. Applying the above commands to install BASS gives:

# assuming that you are in the software repository
cd RoboticPlateform/bass-genom3
genom3 skeleton -i bass.gen
mkdir build && cd build
../configure --prefix=$ROBOTPKG_BASE --with-templates=ros/server,ros/client/c
make install