A fine-grain Phased Logic CPU

Abstract

A five-stage pipelined CPU based on the MIPs ISA is mapped to a self-timed logic family known as Phased Logic (PL). The mapping is performed automatically from a netlist of D-Flip-Flops and 4-input Lookup Tables (LUT4s) to a netlist of Phased Logic gates. Each PL gate implements a 4-input Lookup Table in addition to control logic required for the PL control scheme. PL offers a speedup technique known as Early Evaluation that can be used to boost performance at the cost of additional PL gates. Several different PL gate-level implementations are produced to explore different architectural tradeoffs using early evaluation. Simulations run for five benchmark programs show an average speedup of 1.48 over the clocked netlist at the cost of 17% additional PL gates.