Opportunities and challenges for better than worst-case design

The progressive trend of fabrication technologies towards the nanometer regime has created a number of new physical design challenges for computer architects. Design complexity, uncertainty in environmental and fabrication conditions, and single-event upsets all conspire to compromise system correctness and reliability. Recently, researchers have begun to advocate a new design strategy called better than worst-case design that couples a complex core component with a simple reliable checker mechanism. By delegating the responsibility for correctness and reliability of the design to the checker, it becomes possible to build probably correct designs that effectively address the challenges of deep submicron design. In this paper, we present the concepts of better than worst-case design and highlight two exemplary designs: the DIVA checker and Razor logic. We show how this approach to system implementation relaxes design constraints on core components, which reduces the effects of physical design challenges and creates opportunities to optimize performance and power characteristics. We demonstrate the advantages of relaxed design constraints for the core components by applying typical case optimization (TCO) techniques to an adder circuit. Finally, we discuss the challenges and opportunities posed to CAD tools in the context of better than worst-case design. In particular, we describe the additional support required for analyzing run time characteristics of designs and the many opportunities which are created to incorporate typical-case optimizations into synthesis and verification.