git checkout reusing-profiles

While we have already seen how to reuse other bundles, we have yet to see how to reuse profiles. Indeed, one of the major ideas behind the profile concept is that one can design subsystems that get more and more specialized as their target platform is more and more precise. For instance, bundles/rock_ugv_nav, the bundle that contains models for doing rover navigation in Rock, defines a main navigation profile for all rovers and then specializes it for the 4-wheel skid-steered class of vehicle, vehicles for which Rock has standard components to handle control and odometry.

In the next tutorial, we will want to be able to modify the current definitions so that another component is used in place of the tut_sensor::Task component. This tutorial will guide you through the process of reusing profiles, i.e. create one common profile with the bulk of the definitions and then reuse it in one where tut_sensor::Task is used and another one that will be ready to be filled in the next tutorial. This is also commonly how the split between real and simulated systems is done: a main profile does the common definitions, that then get specialized in the real-robot and in the simulated-robot cases.

We will, in this tutorial, split the Tutorials::Rocks bundle into one profile that handles the current way (without the transformer) and one that uses the transformer-enabled component.

Two main concepts are going to be used for this:

• subclassing (in the Ruby-as-a-programming-language sense of the term) compositions to create more specific versions of them,
• separating files into robot categories in a bundle,
• reusing profiles to refine them

Abstracting the sensor component

The first modification will be to make Tutorials::RockControl independent of the sensor component used. This is of course done by introducing a new data service and using it there instead.

Let’s define first the service in models/blueprints/distance_bearing_sensor_srv.rb

import_types_from 'tut_sensor'
module Tutorials
data_service_type 'DistanceBearingSensorSrv' do
  output_port 'samples', '/rock_tutorial/BearingDistanceSensor'
end
end

And declare in models/orogen/tut_sensor.rb that Task provides it

require 'models/blueprints/distance_bearing_sensor_srv'
TutSensor::Task.provides Tutorials::DistanceBearingSensorSrv,
:as => 'sensor'

Now, if we have a look at the follower specialization for RockControl (in models/blueprints/rock_control.rb)

specialize cmd_child => TutFollower::Task do
add Base::PoseSrv, :as => "target_pose"
add TutSensor::Task, :as => 'sensor'

target_pose_child.connect_to sensor_child.target_frame_port
rock_child.connect_to sensor_child.local_frame_port
sensor_child.connect_to cmd_child
end

we see that a lot of it is actually specific for tut_sensor::Task. If we wanted to stick with specializations, we would create a first specialization for DistanceBearingSensorSrv, and then specialize it for TutSensor::Task. However, this kind of recursive specializations is not supported in Syskit, so we’ll have to deal with it differently.

Instead, we will create a RockFollower composition that is a subclass of RockControl, and specialize it for the different kinds of sensors. Remove the specialize block in RockControl and then add:

# Submodel of RockControl for follower behaviours
class RockFollower < RockControl
overload cmd_child, TutFollower::Task
add DistanceBearingSensorSrv, :as => 'sensor'
sensor_child.connect_to cmd_child

specialize sensor_child => TutSensor::Task do
  add Base::PoseSrv, :as => 'target_pose'
  target_pose_child.connect_to sensor_child.target_frame_port
  rock_child.connect_to sensor_child.local_frame_port
end
end

The existing profile in models/profiles/rocks.rb will have to be changed by replacing RockControl with RockFollower for the follower definition.

Let’s make the result fail with

# syskit instanciate -rtut follower_def!
`block in use': target_pose is not a known child of Tutorials::RockFollower (RuntimeError)

The issue this time is the following:

• we give a selection for ‘target_pose’, which is meant to be a child of RockFollower
• the target_pose child is only defined in the specialization of RockFollower
• nothing in the use() specification allows Syskit to determine that it should specialize.

The solution is therefore to give the sensor component explicitly, so that the specialization is indeed selected:

define 'follower', Tutorials::RockFollower.
use(TutFollower::Task, TutSensor::Task, rock2_dev, 'target_pose' => leader_def)

Reusing Profiles

We will, in the next tutorial, also want to use TutSensor::TransformerTask as a possible sensor. Let’s make this possible right now.

In models/orogen/tut_sensor.rb, add

TutSensor::TransformerTask.provides Tutorials::DistanceBearingSensorSrv,
  :as => 'sensor'

There are now two possible components for DistanceBearingSensorSrv. We could simply create a new definition for TutSensor::TransformerTask. However, we will use this situation to explain how to reuse profiles instead.

What we are going to do now is create a base profile that is common between the non-transformer and the transformer-enabled cases. Then, we will have the RocksWithoutTransformer profile on the one hand, and the RocksWithTransformer on the other hand. Finally, we will create two robot configurations: one that uses the transformer and one that does not.

First part: creating the Base profile. This is trivially done by renaming the Rocks profile into BaseRocks, and modify the follower definition to be independent of the sensor type.

profile 'BaseRocks' do
...
define 'follower', Tutorials::RockFollower.
  use(TutFollower::Task, rock2_dev)
end

Second part: making the two profiles, one that is identical to the one we had so far, and one for the transformer case. To achieve this, we create two new Rocks profile and tell Syskit that they use the base one. Finally we add some more dependency selection that is then limited to these new profiles. At the end, we refine the follower definition in the no-transformer case to match what we had beforehand.

profile 'RocksWithoutTransformer' do
use_profile BaseRocks
define 'follower', follower_def.use(TutSensor::Task, 'target_pose' => leader_def)
end
profile 'RocksWithTransformer' do
use_profile BaseRocks
define 'follower', follower_def.use(TutSensor::TransformerTask)
end

Finally create the two robot configurations. We now need to have a way to select which profiles to apply from the command line. This is done through Roby’s robot configuration mechanism.

We’ll keep the ‘tut’ robot as our non-transformer robot. Let’s now create a new tut-transformer robot for the other case:

roby add-robot tut-transformer

What we did so far is use the Rocks profile in models/actions/main.rb. Since this is the action definition for all the robots, we need to move the use_profile statement into models/actions/tut/main.rb (don’t forget to rename Rocks into RocksWithoutTransformer), which is specific to the tut robot. And do the corresponding modification in models/actions/tut-transformer/main.rb

require 'models/profiles/rocks'
class Main < Roby::Actions::Interface
use_profile Tutorials::RocksWithTransformer
end

We also should not forget to add the use_deployments line in config/tut-transformer.rb (it is at the top of config/tut.rb). The transformer case is now available by selecting the tut-transformer robot:

syskit instanciate -rtut-transformer follower_def!

Conclusion

The profile-reusing mechanism creates scopes for definitions and selections of tasks for services. This scoping mechanism applies to all the profile elements, such as robot definition blocks or transformer configuration. In other words: if it is defined in a profile, it is scoped to this particular profile.

We can now finally move to the transformer tutorial