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Benefits of architectural modelling in embedded design

Posted: 27 Nov 2014     Print Version  Bookmark and Share

Keywords:Simulink  AUTOSAR  EAST-ADL  state machine  architecture modelling 

Within an error model, there is a precise description of the internal failure modes of components and their propagations to other system failure modes. In figure 11 the connection links represent the error propagations due to communication links or allocation relations in the design.

To facilitate safety engineering, MetaEdit+ can automatically create an initial setup of such error models according to a nominal architecture model. Within each error model block, engineers then specify error logic relating the declared component output failures to the received and local faults. The exact formalism can be based on a Boolean logic expression or state machine (SM).

 Error model

Figure 11: Error model defining the plausible error behaviour of target system architecture. (Click on image to enlarge)

Within MetaEdit+, a model transformation gateway is developed to parse the error model and generate the corresponding analytical model. Figure 12 shows the result of such a model transformation, from the EAST-ADL error model shown in figure 11 to a model of the external safety analysis tool HiP-HOPS.

Figure 12 also shows the resulting fault tree where the failure modes are originally captured and maintained in the EAST-ADL error model shown in figure 11. For example, the root event braking_failure_AL is originally defined as the output of the rightmost block in figure 11. The resulting fault tree together with a list of minimal cut sets constitutes a solid basis for the elicitation of functional and technical safety requirements.

 Error model

Figure 12: The exported HiP-HOPS file and the analysis result fault tree. (Click on image to enlarge)

Conclusion
Architecture models offer several additional benefits compared to the traditional use of models focusing on implementing a single feature. Most visible is that they allow the design of the larger system as an integrated whole. Supporting tools then enable team members to create and edit the architecture in a collaborative and concurrent manner. Architecture models also help in managing the development activities, which often involve dozens of suppliers: Individual parts can be split among various teams and the resulting implementations can be integrated and checked with the whole architecture.

The architecture models provide an ideal basis for analysis and evaluation of the system to be built – and at an early stage, where changes are cheaper and easier. The analysis of the models can include checking, error analysis and support for safety design. These allow engineers to evaluate different system level designs and automatically run analysis results, as we demonstrated for the case of model checker tools and fault-tree analysis. Having the possibility to run such analysis earlier provides major benefits, not only in development cost savings or improved quality, but also in faster time to market.

Requirements management integrates well with architecture models, as many of the requirements align cleanly to the higher-level elements defined in the architecture, such as functions or their connections. Creating the alignment between existing requirements and architecture can be supported by tooling, as demonstrated in this article.

Reaping the benefits of architecture models does not require creating the architecture separately or ahead of time. Tools are already available today that can automate significant parts of the task, like creating the initial architecture based on an existing implementation. The tools can check the resulting architecture models against existing implementations, or generate the interfaces for the implementations to be developed. The generators may also produce the configurations and mapping to the target platforms used, such as AUTOSAR, JasPar, or internal platforms.

As system size and complexity grow, tool support is becoming ever more important. No single tool can cover the whole life cycle, nor all possible domains or kinds of systems. To achieve the benefits of architecture models, companies need best-of-breed tools that each have a solid base, can be configured for their needs, and can be integrated into a coherent tool chain.

About the author
Dr. Juha-Pekka Tolvanen is CEO of MetaCase. He has been involved in domain-specific languages and tools since 1991 and acted as a consultant world-wide on their use. Juha-Pekka has co-authored a book (Domain-Specific Modeling, Wiley 2008) and over 80 articles in software development magazines and conferences.

De-Jiu Chen received his PhD degree in Mechanical Engineering from Swedish Royal Institute of Technology (KTH) in 2004 for his research on embedded computer control systems. His research interests include systems and software architecture, model-based engineering, dependability, and self-adaptive embedded systems. He is currently an associate professor at KTH.

Janne Luoma (M.Sc.) works as senior consultant at MetaCase Consulting. His area of expertise is in the engineering of software development methods for company-specific needs. Janne has over 15 years of experience as a consultant world-wide for method development and code generators.


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