Internal design representations for embedded systems

Modern embedded computing systems tend to be heterogeneous assemblages of concurrent subsystems, typically described in different languages and semantics which are well established in the various application fields. For example, the specification of the functional and timing behavior necessitates a mixture of different basic models of computation and communication which come from transformatlive or reactive domains. There is little hope that a single language will replace this heterogeneous set of languages. In fact, experiments with system specification languages show that there is not a unique universal specification language to support the whole life cycle. A similar problem occurs when reused components shall be integrated, possibly described in another language and incompletely documented. Examples would be components of other companies or "legacy code". The lack of coherency of the different languages, methods and toots is a substantial obstacle on the way to higher design productivity and design quality. A design process must be able to bridge the semantic differences for verification and synthesis and should account for limited knowledge of system properties. This paper describes approaches which allow for the common representation of different languages and incomplete specifications. In particular, recent results on the use of internal design representations targeted to scheduling and design space exploration are reviewed. The information useful for methods like allocation of resources, partitioning the design and scheduling must be estimated or extracted from the various input languages and mapped onto internal representations which describe properties of the subsystems and their coordination. Design methods work on these internal representations and eventually refine them by adding components and reducing non-determinism.