Eecient Optimal Design Space Characterization Methodologies

One of the primary advantages of a high-level synthesis system is its ability to explore the design space. This paper presents several methodologies for design space exploration that compute all optimal tradeoo points for the combined problem of scheduling, clock length determination, and module selection. We discuss how each methodology takes advantage of both the structure within the design space itself as well as the structure of, and interaction between, each of the three subproblems. 1. INTRODUCTION For many years, one of the most compelling reasons for developing high-level synthesis systems Gajski et al. 1994] De Micheli 1994] has been the desire to quickly explore a wide range of designs for the same behavioral description. Given a set of designs, two metrics are commonly used to evaluate their quality: area (ideally total area, but often only functional unit area), and time (the schedule length, or latency). Finding the optimal tradeoo curve between these two metrics is called design space exploration. Design space exploration is generally considered too diicult to solve optimally in a reasonable amount of time, so the problem is usually limited to computing either lower bounds Timmer et al. 1993] or estimates Chen and Jeng 1991] on the optimal tradeoo curve for some set of time or resource constraints. Moreover, the design space is usually determined by solving only the scheduling and functional unit allocation subproblems. The design space exploration methodology described here goes beyond traditional design space exploration in several ways. First, all optimal tradeoo points are computed so that the design space is completely characterized. Second, these optimal tradeoo points represent optimal solutions to the time-constrained scheduling (TCS) and resource-constrained scheduling (RCS) problems, rather than lower bounds or estimates. Third, the tradeoo points are computed in a manner that supports more realistic module libraries by incorporating clock length determination and module selection into the methodology. Finally, these tradeoo points are