Late-Stage Optimization of Modern ILP Processor Cores via FPGA Simulation

Abstract

Late-stage (post-RTL implementation) optimization is important in achieving target performance for realistic processor design. However, several challenges remain for modern out-of-order ILP (instruction-level-parallelism) processors, such as simulation speed, flexibility, and complexity problems. This paper restudy FPGA simulation as an effective performance simulation method and proposes FPGA-enhanced design flow as an effective method to address these problems. It features a late-stage aware RTL design that parameterizes various potential design options induced from early-stage optimization. This flow enables the feasibility of late-stage design space exploration. To resolve the performance accuracy of the FPGA system for peripheral designs, reference models are introduced. With an example implementation of out-of-order core running up to 80 MHz, the experimental results show that the proposed method is practical and allows the fine-grain optimization of the processor core to be more effective.