Exploration and Customization of FPGA-Based Soft Processors

As embedded systems designers increasingly use field-programmable gate arrays (FPGAs) while pursuing single-chip designs, they are motivated to have their designs also include soft processors, processors built using FPGA programmable logic. In this paper, we provide: 1) an exploration of the microarchitectural tradeoffs for soft processors and 2) a set of customization techniques that capitalizes on these tradeoffs to improve the efficiency of soft processors for specific applications. Using our infrastructure for automatically generating soft-processor implementations (which span a large area/speed design space while remaining competitive with Altera's Nios II variations), we quantify tradeoffs within soft-processor microarchitecture and explore the impact of tuning the microarchitecture to the application. In addition, we apply a technique of subsetting the instruction set to use only the portion utilized by the application. Through these two techniques, we can improve the performance-per-area of a soft processor for a specific application by an average of 25%