Abstract

This tutorial will teach you:

• how to create a data driven component
• how to connect multiple components

The data driven component that is designed in this tutorial waits for incoming messages and outputs their content once it receives a message. The incoming messages will be produced by the message_producer component designed in the previous tutorials.

The final setup will look like:

Create a consumer component

Your first task in this tutorial is to apply the acquired knowleged from the previous tutorials, and prepare a consumer component named ‘message_consumer’ and place in ‘basics_tutorial/orogen/’. Perform all step up to the point where you can edit the orogen specification, i.e.:

• use rock-create-orogen to create your component (note: you will need a dependency on both message_driver and message_producer)
• check for any required dependencies and verify the manifest.xml
• add your component to the build configuration, i.e. to autoproj/manifest

The next step will be to adapt the orogen specification. The component should allow to receive messages on an input port, and call the updateHook only when it receives a message. The specification should looks as follows:

using_library "message_driver"
import_types_from "message_producer"

task_context "Task" do
   input_port "messages", "message_driver/Message"

   port_driven "messages"
end

The ‘port_driven’ statement allows you to specify ports, where incoming data triggers a call to the updateHook of the task (more details in the documentation). Implement the updateHook, so that every incoming message is printed to stdout, using the existing printMessage function of your ‘message_driver’ library.

void Task::updateHook()
{
    TaskBase::updateHook();
    
    message_driver::Message message;
    _messages.read(message);

    mpMessageDriver->printMessage(message);
}

Build your component with ‘amake’.

Connecting multiple components

You have designed a component that produces messages and a component that consumes messages. To connect them, you will use the Ruby scripting interface. Create a file start.rb in your consumer component’s script folder (you will have to create the folder first) with the following content:

require 'orocos'
require 'readline'

include Orocos
Orocos.initialize


Orocos.run 'message_producer::Task' => 'message_producer', 
    'message_consumer::Task' => 'message_consumer' do  
  
  message_producer = TaskContext.get 'message_producer'
  message_consumer = TaskContext.get 'message_consumer'
  
  # Never assume that a component supports being reconnected
  # at runtime, it might not be the case
  #
  # If you have the choice, connect before the component is
  # even configured
  message_producer.messages.connect_to message_consumer.messages
  
  message_producer.configure
  message_producer.start
  
  message_consumer.start
  
  Readline::readline("Press ENTER to exit\n") do
  end 
end

The call to ‘connect_to’ for an output port allows you to connect it with an input port. By default a data connection is created, but you can also specify the type of your connection explicitly. Check the documentation for more details on that topic.

Run it

Run your ruby script

ruby start.rb

If everything has been done correctly, you will eventually see the consumer printing messages to the console, in the periodicity you set on the message producer:

[20110803-10:59:55:068] Message from MessageDriver
[20110803-10:59:56:068] Message from MessageDriver
[20110803-10:59:57:068] Message from MessageDriver
[20110803-10:59:58:068] Message from MessageDriver

As usual, shut it down with CTRL+C. The script does the cleanup itself.

Summary

In this tutorial you have learned to:

• create a component that is triggered upon receiving incoming data, i.e. you know now how to design a port/data driven component
• run two components using a single ruby script
• connect two components by connecting an output and an input port with a default data connection

Progress to the next tutorial.