Let's recap what we've seen in this Basics section.


Autoproj is Rock's tool to manage (install and update) packages. "Packages" are the unit of integration of the Rock software. The role of a workspace build configuration is to ensure repeatability in the installation of a system's software

You will ultimately create your own build configuration and package sets to share the state of your workspace with your coworkers.


Bundles are the package within which we create Syskit models and code. It is the place of integration.

From Syskit's point of view, a bundle has a toplevel namespace under which the rest of the app is defined. It is by default the CamelCased version of the bundle's folder name (syskit_basics becomes SyskitBasics).

A given bundle may contain multiple Syskit app configurations. The entry point for each configuration is a file in config/orogen/. One usually creates one bundle per class of system, and creates at least one configuration for simulation and one for the live system. Syskit tools take a -rROBOT_NAME argument to specify which configuration should be loaded.

It is possible to reuse models from another bundle by using either globally in config/init.rb or per-robot in the Robot.init block of the robot configuration file. Example

Within bundles:

  • separate SDF models are saved within models/sdf/
  • SDF scenes are saved within scenes/#{scene_name}/#{scene_name}.world
  • compositions are in models/compositions/
  • ruby tasks are in models/compositions/
  • orogen extension files are in models/orogen/
  • profiles are in models/profiles/
  • orogen configuration files are in config/orogen/. Configuration-specific files (e.g. in config/orogen/gazebo/) take precedence.
  • within the Syskit model folders (compositions/ and profiles/), the convention is to have subfolders for models that are specific to a given robot configuration (e.g. profiles/gazebo/ for models that are specific to the gazebo configuration). The generators enforce this when given the -rROBOT_NAME option.
  • the folder structure in models/ maps one-to-one to the folder structure in test/

Components and Compositions

Components are the basic construction block in a Syskit system. Compositions are used to turn single components into more complex functional units, by binding the components together.

  • a composition template is created using

    syskit gen NameOfComposition
  • an element within a composition is declared with add, a component model (which can be another composition) and a name:

    class MyComposition < Syskit::Composition
      add AnotherComponentModel, as: 'generator'
  • within the composition model, a composition child is accessed using the child's name and the _child suffix. Ports are accessed with the port name and the _port suffix. This is how connections are made:

    source_child.out_port.connect_to sink_child.in_port
  • a composition can have ports, which are exports of its children ports. This works for both input and output ports. The exported port name is the same as the child's port name, but this can be overriden

    export source_child.out_port
    export another_source_child.out_port, as: 'another'

oroGen components

oroGen is Rock's way to package C++ functionality into ready-to-use components with a standardized interface. These components are imported in Syskit's with

using_task_library "name_of_orogen_project"

The other role of oroGen is to define types whose instances can be transferred between components. If one only wants to use a type defined by an oroGen project, but without using the associated components, one does

import_types_from "name_of_orogen_project"

The corresponding types are accessible under the Types object, e.g.


On import, Syskit builds a component model that represents the oroGen component. This model is accessible as OroGen.project_name.TaskName. It can also be extended to reflect needs in the Syskit app, for instance configuration, using extension files.

oroGen components provide a configuration interface as a set of properties. These properties are filled using YAML configuration files stored in config/orogen/, and may also be written in the configure method of the component's class, in the extension file.

A configuration file for a component class is generated with

syskit gen orogenconf name_of_orogen_project::NameOfModelClass

Ruby Tasks

In a system, one often needs to do some small tasks that are either too small to warrant a full-fledged C++ component, or are so tied with the system integration that having a C++/Ruby boundary makes understanding hard. For these, Syskit allows to implement tasks in Ruby that are integrated within the Syskit execution but provide input and output ports to integrate with the rest of the components.

Because of the single-threaded nature of Syskit's execution engine, one must not use ruby tasks to perform a lot of work. This would freeze Syskit. Stick to simple tasks, and implement oroGen components for more complex ones.

A canonical example for such a task is the common_models bundle's ConstantGenerator.

Whenever runtime code is present in tasks, as it often is in ruby tasks, write tests.

A new Ruby task and associated test scaffold is generated with

syskit gen ruby_task class_name


Profiles are the models that contain functional networks. It is common to have compositions made of abstract models, that is components that are not really components - such as device models. These abstract components can be replaced by actual components within the profiles with the use call. Moreover, profiles allow to specify arguments to compositions in the process of definition.

The model name given to define in a profile is made out of a demeter chain. In Ruby, one can easily break the chain with a newline after each method call. Don't forget the dots !

  • arguments are set with with_arguments

    CompositionModel.with_arguments(arg_name: arg_value)
  • CompositionModel.use('child_name' => model) replaces CompositionModel's child_name child with the given model. model can itself be refined by use and with_arguments.
  • CompositionModel.use(model) replaces any CompositionModel child whose model is compatible with model by model.
  • a definition or device can itself be used as model or CompositionModel in all these calls, possibly from another profile:

    define 'first', CompositionModel.use(first_test_dev)
    define 'second', first_dev.use(AnotherProfile.second_test_dev)
    define 'third', AnotherProfile.first_dev.use(second_test_dev)


Apart from the orogen configuration files, components can have arguments. The choice between a configuration file or a component argument is a matter of system design, but there are some guidelines.

Use task arguments when

  • consistency between different components is necessary, as for instance the robot model
  • a value is to be provided at runtime, as for instance a target pose

Use configuration files when

  • the values are static (set once and seldom changed)

Arguments can be forwarded from a composition to its children using the following pattern:

class C < Syskit::Composition
  argument :robot
  add(ChildModel, as: 'generator').
    with_arguments(robot: from(:parent_task).robot)

Deployments, Actions

Before they are used, components need to be deployed, that is associated with a process and a name. This is done in the requires block of the robot configuration file with

Syskit.conf.use_deployment ComponentModel => 'component_name'

Actions are the basic block of interaction between a Syskit app and the outside world. Moreover, the Main action interface, defined by the actions block in the robot configuration file is the interface that is being exposed through the standard channels (IDE, shell).

Definitions from a profile are exported on the Main interface.

Next: We've only had a glimpse on the Syskit runtime workflow. Let's dig deeper