An Area-Efficient Out-of-Order Soft-Core Processor Without Register Renaming

In this paper, we present an out-of-order soft-core processor adopting STRAIGHT architecture. STRAIGHT has a unique instruction format in which source operands are expressed as distances from producer instructions. This eliminates the need for register renaming and eliminates a register map table (RMT), which usually consists of a large multi-port RAM. That leads to small area, low power consumption, and high scalability of the front-end pipeline width. Moreover, the simplified architecture enables rapid miss-recovery. The prototype is implemented and evaluated on an FPGA. Compared to an out-of-order soft-core processor with a conventional RISC ISA, the proposed soft-core consumes 147-829 fewer LUTs for the front-end pipeline. The evaluation results show that the proposed soft-core is correctly operating on an FPGA, and estimated dynamic power consumption of the soft-core is 0.120 W.