Integrating Operational Specification and Performance Modeling for Digital-System Design

While evolving from an abstract concept into a detailed implementation, the design of a complex digital system proceeds through different design stages. Due to lack of effective communication of design intent among these stages, errors are introduced in the product. Early detection of such errors is crucial for increasing robustness and reducing design costsof the final product.
To facilitate early detection, a design methodology must support model continuity. Model continuity comprises three subproblems:
• Complementary modeling: modeling different aspects of the system under design in different modeling domains concurrently,
• Back annotation: incorporating design details obtained during later stages back into the models developed during earlier stages, and
• Conformance checking: ensuring conformance of models across various design stages.
We address the problem of model continuity in the context of reactive systems through the integration of operational specification and performance models. Complementary modeling is supported through integrated simulation of the two models. Both models execute concurrently, exchanging data and simulation stimuli with each other. Back annotation is supported through a novel technique, called performance annotation. This technique allows the dynamic incorporation of delay-related information in an implementation-independent manner from a concurrently executing performance model. Finally, conformance checking is performed by a simulation-based algorithm. Similar to the comparison-checking technique found in the context of software design diversity, this algorithm checks the operational-specification and performance models by comparing their output sequences against each other. However, we also address situations when the output sequences can be quite different even if the models conform, and prove that the algorithm correctly determines all conformance violations, under certain design assumptions, during a simulation session.
Integration of operational specification and performance models gives rise to a novel design methodology. Starting from an operational specification, the designer proposes an implementation in an incremental and iteratively-refined manner. Using this methodology, we demonstrate how one can validate an implementation against its specification, remove ambiguities in the original specification, and obtain very early performance estimates for a system under design.