Code Generation Tutorial

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Tutorial Overview

The aim of the tutorial is to allow users to explore the approach with a relatively simple example. The example uses a shared buffer with reader and writer processes. The tutorial is presented in three stages, making use of the example projects from the download site. There are two translations performed, one is to a common language model (IL1). The second is to an Event-B project which includes a model of the implementation. There is a PrettyPrinter for Ada source code, which uses the common language model.

A typical Event-B development may be refined to the point where it is ready for implementation, but the Event-B language is not expressive enough to fully describe the implementation. Tasking Event-B facilitates this final step to implementation, by extending Event-B with the necessary constructs. Event-B machines that are to be implemented (and their seen Contexts) are selected and added to a Tasking Development; the Tasking Development files have the file extension .tasking. The machines in the Tasking Development are then extended with implementation details.

The example/tutorial projects are,

SharedBuffer20100819Demo	An example project with a completed Tasking Development and IL1 model (post IL1 translation, but before Event-B translation).
Sharedbuffer20100819Tasking	Same as the example project above, but with Event-B model translations. The difference being that this development includes a model of the implementation. These are refinements that include a program counter to describe flow of execution in each task.
SharedBuffer20100819Tutorial	A bare project for step 1 of the tutorial.
Sharedbuffer20100819Tutorial2	A partially completed tasking development for steps 2 and 3 of the tutorial.

Preliminaries

Before further discussion of the modelling aspects, we take a look at the PrettyPrint viewers. The PrettyPrinters make the viewing of IL1 and tasking models easier; it also provides a route to generate source code. The source code can easily be pasted from the IL1 Pretty Printer window into an the Ada source file .

The PrettyPrint View of a Tasking Development

To open the Tasking PrettyPrint viewer,

• from the top-menu select Window/Show View/Other/Tasking Pretty Printer.

Note that the Tasking PrettyPrinter may have to be closed when editing the Tasking Development, since it can give rise to exceptions. The PrettyPrinter would need further work to make it robust, however it is intended only as a short-term solution.

• Open the SharedBuffer20100819Demo Project and switch to the Resource Perspective.
• Open the .tasking model and inspect it. Clicking on the Main, Machine or Event nodes updates the pretty print window.

Viewing Source Code

aka. The PrettyPrint View of an IL1 Model.

To view Ada source code,

• from the top-menu select Window/Show View/Other/IL1 Pretty Printer.
• Open the SharedBuffer20100819Demo Project and switch to the Resource Perspective.
• Open the .il1 model and inspect it. Clicking on the Protected, Main Entry, or Task nodes updates the pretty print window.

Cleaning the Tasking Development

If the .tasking file has errors, then it may need cleaning. To do this right-click on the Main node, select Epsilon Translation/CleanUp. If a model has errors it can still be viewed by clicking on the Selection tab at the bottom of the tasking editor window.

The Tutorial

The steps needed to generate code from an Event-B model, in this tutorial, are as follows,

• Step 1 - Create the tasking development.
• Step 2 - Add annotations.
• Step 3 - Invoke translators.

Creating The Tasking Development

• Change to the Event-B Perspective.
• Open the SharedBuffer20100819Tutorial Project.
• Select the following Machines: Reader, Writer and Shared.
• Right-click and select Make Tasking Development/Generate Tasking Development.

The new Tasking Development will not be visible in the Event-B perspective, change to the resource perspective, open and inspect the new .tasking file. The Tasking Development contains (the EMF representation of) the machines that we wish to provide implementations for. In order to introduce the new concepts we have prepared a partially complete development.

Change to the Project SharedBuffer20100819Tutorial2 to begin the next step.

Providing the Annotations for Implementations

• Close any Tasking Pretty Print Viewers that remain open. The incomplete model will give rise to exceptions.
• Go to the to the Resource Perspective.
• Open and inspect the .tasking machine.

The WriterTsk and SharedObj machines are incomplete. We will take the steps to necessary to provide implementation details.

The first task is to identify the SharedMachine type. The SharedObj Machine will be extended.

• Right-click on the SharedObj Machine node in the .tasking file.
• Select new child/Extension.