It is well known that techniques such as performance modeling that can effectively evaluate design alternatives early in the design process can greatly increase the quality of the ultimate implementation, while at the same time, decrease the design time. In order to gain the maximum benefit from performance modeling, it must be integrated into the design process such that the performance model can be directly refined into an implementation. This paper presents techniques for developing interfaces between abstract performance models and detailed behavioral models to enable this refinement process. These mixed-level modeling interfaces, as they are called, allow abstract performance models to be cosimulated with detailed behavioral models. Because of the differences in the level of detail between abstract performance models and detailed behavioral models, not all of the inputs to the behavioral model can be derived from information in the performance model. Techniques for determining values for these "unknown" inputs are presented, These techniques have been designed to generate bounds on the system performance that converge as the model is refined.

This paper presents an integrated design environment thatsupports the design and analysis of digital systems from initialconcept to the final implementation. The environment supports bothsystem level performance and dependability analysis from acommon modeling representation. A tool called ADEPT (AdvancedDesign Environment Prototype Tool) has been developed toimplement the environment. ADEPT is based on IEEE 1076 VHDLand uses commercial schematic capture systems as a front end viaan EDIF interface. Several examples are presented whichdemonstrate various aspects of the environment.

The design of complex systems requires an enormous amount of modeling and simulation at the various levels of detail to assure high quality results. Most design methodologies require the use of separate modeling languages and simulation environments for each refinement step and simulation technique. Since one of the major goals of design is to reduce the time to market for a given system, the current approaches are becoming unacceptable. A new unified modeling (UM) methodology is under development at the University of Virginia which provides a top-down/bottom-up design methodology based on a single modeling environment. This single environment methodology is made possible through a technique known as hybrid modeling, which enable the simulation and analysis of behavioral components within a system-level model. By simulating behavioral components along with components at the system modeling level, high risk portions of the design can be examined at earlier stages in a given product's development; thus reducing the time to market. The paper examines the hybrid modeling techniques which make this multi-level modeling possible.