Application-specific programmable control for high-performance asynchronous circuits

The advantages of the programmable control paradigm are widely known in the design of synchronous sequential circuits: easy correction of late design errors, easy upgrade of product families to meet time-to-market constraints, and modifications of the control algorithm, even at run time. However, despite the growing interest in asynchronous (self-timed) circuits, programmable asynchronous controllers based on the idea of microprogramming have not been actively pursued. In this paper, we propose an asynchronous microprogrammed control organization (called a microengine) that targets application-specific implementations and emphasizes simplicity, modularity, and high performance. The architecture takes advantage of the natural ability of self-timed circuits to chain actions efficiently without the clock-based scheduling constraints that would be involved in comparable synchronous designs. The result is a general approach to the design of application-specific microengines featuring a programmable data-path topology that offers very compact microcode and high performance-in fact, performance close to that offered by automated hardwired controllers. In performance comparisons of a CD-player error decoder design, the proposed microengine architecture was 26 times faster than the general purpose hardware of a 280 MIPS microprocessor, over three times as fast as the special purpose hardware of a low-power macromodule based implementation, and even slightly faster than a finite state machine-based implementation.