Asynchronous processor survey

Virtually all computers today are synchronous. As systems grow increasingly large and complex the clock can cause big problems with clock skew, a timing delay that can create havoc with the overall design. It can also increase the circuit silicon and power dissipation, which can affect overheating and power supplies. Computer architecture researchers are actively considering asynchronous processor design. Asynchronous architectures permit modular design. Each subsystem or functional block can be optimized without being synchronized to a global clock, which simplifies interfacing. Moreover, an asynchronous system exhibits the average performance of all the individual components, rather than the synchronous system's worst-case performance of a single component. Furthermore, asynchronous processors may yet prove to offer reduced power dissipation by inherently shutting down unused portions of the circuit. This article examines the key architecture issues that concern designers and compares six developmental asynchronous architectures: CAP, the Caltoch Asynchronous Processor; FAM, the Fully Asynchronous Microprocessor; NSR, the Nonsynchronous RISC; CFPP, the Counterflow Pipeline Processor; Strip, a Self-Assured RISC Processor; and Amulet 1.