D32 Code generation
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General Overview
The code generation activity has been undertaken at the University of Southampton. This has been a new line of work for DEPLOY that was not identified in the original Description of Work for the project. The development of the approach, and the tools to support, it involved a number of team members at Southampton; and also at other institutions. This work draws on our recent experience with technologies such as Shared Event Decomposition [1], and the EMF Framework for Event-B [2]. There was collaboration at an early stage with Newcastle University, where we explored the commonalities between their flow plug-in [3] and the algorithmic structures used in our approach. Collaboration with the University of York was also established since we chose to use their Epsilon [4] model-to-model transformation technology.
Motivations
The decision was taken in 2009 to include code generation as a project goal [5]. It had been recognised that support for generation of code from refined Event-B models would be an important factor in ensuring eventual deployment of the DEPLOY approach within their organisations. This was especially true for Bosch and Space Systems Finland (SSF). After receiving more detailed requirements from Bosch and SSF, it became clear we should focus our efforts on supporting the generation of code for typical real-time embedded control software.
Choices / Decisions
Strategic Overview
During the last year we have focussed on supporting the generation of code for typical real-time embedded control software. To this end we have evolved a multi-tasking approach which is conceptually similar to that of the Ada tasking model. Individual tasks are treated as sequential programs; these tasks are modelled by an extension to Event-B, called Tasking Machines. Tasks have mutually exclusive access to state variables through the use of protected resources. The protected resources correspond to Event-B machines. For real-time control, periodic and one-shot activation is currently supported; and it is planned to support aperiodic tasks in the near future. Tasks have priorities to ensure appropriate responsiveness of the control software. For the DEPLOY project, it was regarded as sufficient to support construction of programs with a fixed number of tasks and a fixed number of shared variables – no dynamic creation of processes or objects has been accommodated.
Our main goal this year has been to devise an approach for, and provide tool support for, code generation. In accord with the resources available during the year it was decided to limit the provision of tool support to that of a demonstrator tool. The tool is a proof-of-concept only, and lacks the productivity enhancements expected in a more mature tool. Nevertheless much insight has been gained in undertaking this work; it lays a foundation for future research, and will be useful since it will allow interested parties to explore the approach.
The Tasking Extension for Event-B
The following text can be read in conjunction with the slides[6] from the Deploy Plenary Meeting - Zurich 2010.
Tasking Event-B can be viewed as an extension of the existing Event-B language. We use the existing approaches of refinement and decomposition to structure a development that is suitable for construction of a tasking development. At some point during the modelling phase parameters may have to be introduced to facilitate decomposition. This constitutes a natural part of the refinement process as it moves towards decomposition and on to the implementation level. During decomposition parameters form part of the interface that enables event synchronization. We make use of this interface and add information (see #Events For Tasking) to facilitate code generation.
A tasking development is generated programmatically, at the direction of the user; the tasking development consists of a number of machines (and perhaps associated contexts). In our approach we make use of the Event-B EMF extension mechanism which allows addition of new constructs to a model. The tasking extension consists of the constructs in the following table.
| Construct | Options |
| Machine Type | Declared Task, AutoTask, Shared Machine |
| Control | Sequence, Loop, Branch, EventSynch |
| Task Type | Periodic(n), Sporadic, Repeating, One-shot |
| Priority | - |
| Event Type | Branch, Loop, ProcedureDef, ProcedureSynch |
| Parameter Type | ActualIn, ActualOut, FormalIn, FormalOut |
The machines in the tasking development are extended with the constructs shown in the table. With extensions added, a tasking development can be translated to a common language model for mapping to implementation source code. There is also a translator that constructs an Event-B model which models the implementation, and this should refine the preceding models in the development.
Tasking - Algorithmic Constructs
- Tasking constructs:
- Sequence, Branch, Loop.
- Event-wrappers.
- Event Synchronisation.
Events For Tasking
Event implementation. Branch, Loop, ProcedureSych, ProcedureDef
Event parameter types. FormalIn FormalOut, ActualIn, ActualOut
Tasking Machines
Auto-Tasks.
Declared tasks.
Task type.
Task priority.
Events can only be ProcedureDef or ProcedureSynch
Parameters of ProcedureSynch can only be FormalIn or FormalOut
ProcedureDef - parameters not allowed.
Other Technical Issues
Meta-models: The use of Epsilon for translation.
The Deliverable
The demonstrator tool was released on 30 November 2010, and is available as an update site, or bundled Rodin package from:
https://sourceforge.net/projects/codegenerationd/files
Sources are available from:
https://codegenerationd.svn.sourceforge.net/svnroot/codegenerationd
The tool is based on a build of Rodin 1.3.1 (not Rodin 2.0.0 due to dependency conflicts).
- The Code Generation tool consists of,
- a tasking Development Generator.
- a tasking Development Editor (Based on an EMF Tree Editor).
- a translator, from Tasking Development to Common Language Model (IL1).
- a translator, from the Tasking Development to Event-B model of the implementation.
- a pretty-printer for the Tasking Development.
- a pretty-printer for Common Language Model, which generates Ada Source Code.
Available Documentation
pre study http://eprints.ecs.soton.ac.uk/20826/
paper http://eprints.ecs.soton.ac.uk/20824/
wiki page http://wiki.event-b.org/index.php/Code_Generation_Activity
tutorial http://wiki.event-b.org/index.php/Code_Generation_Tutorial
technical notes http://wiki.event-b.org/images/Translation.pdf
This paragraph shall give pointers to the available wiki pages or related publications. This documentation may contain:
* Requirements. * Pre-studies (states of the art, proposals, discussions). * Technical details (specifications). * Teaching materials (tutorials). * User's guides.
A distinction shall be made on the one hand between these different categories, and on the other hand between documentation written for developers and documentation written for end-users.
Planning
This paragraph shall give a timeline and current status (as of 28 Jan 2011).
