Variable-latency design by function speculation

Abstract

Variable-latency designs may improve the performance of those circuits in which the worst-case delay paths are infrequently activated. Telescopic units emerged as a scheme to automatically synthesize variable-latency circuits. In this paper, a novel approach is proposed that brings three main contributions with regard to the methods used for telescopic units: first, no multi-cycle timing analysis is required to ensure the correctness of the circuit; second, the method can be applied to large circuits; third, the circuit can be optimized for the most frequent input patterns. The approach is based on finding approximations of critical nodes in the netlist that substitute the exact behavior. Two cycles are required when the approximations are not correct. These approximations can be obtained by the simulation of traces applied to the circuit. Experimental results on selected examples show a tangible speed-up (15%) with a small area overhead (3%).