A solid design flow must capture designs at well-defined levels of abstraction and proceed toward an efficient implementation. The critical decisions involve the system's architecture, which will execute the computation and communication tasks associated with the design's overall specification. Understanding the application domain is essential to ensure efficient use of the design flow. Today, the design chain lacks adequate support. Most system-level designers use a collection of unlinked

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... . The implementation then proceeds with informal techniques that involve numerous human-language interactions that create unnecessary and unwanted iterations among groups of designers in different companies or different divisions. These groups share little understanding of their respective knowledge domains. Developers thus cannot be sure that these tools, linked by manual or empirical translation of intermediate formats, will preserve the design's semantics. This uncertainty often results in errors that are difficult to identify and debug. The move toward programmable platforms shifts the design implementation task toward embedded software design. When embedded software reaches the complexity typical of today's designs, the risk that the software will not function correctly increases dramatically. This risk stems mainly from poor design methodologies and fragile software sys-tem architectures, the result of growing functionality over an existing implementation that may be quite old and undocumented. The Metropolis project seeks to develop a unified framework that can cope with these challenges. DESIGN OVERVIEW We designed Metropolis to provide an infrastructure based on a model with precise semantics that remain general enough to support existing computation models 1 and accommodate new ones. This metamodel can support not only functionality capture and analysis, but also architecture description and the mapping of functionality to architectural elements. Metropolis uses a logic language to capture nonfunctional and declarative constraints. Because the model has a precise semantics, it can support several synthesis and formal analysis tools in addition to simulation. The first design activity that Metropolis supports, communication of design intent and results, focuses on the interactions among people working at different abstraction levels and among people working concurrently at the same abstraction level. The metamodel includes constraints that represent in abstract form requirements not yet implemented or assumed to be satisfied by the rest of the system and its environment. Based on a metamodel with formal semantics that developers can use to capture designs, Metropolis provides an environment for complex electronic-system design that supports simulation, formal analysis, and synthesis.