Ultrasmall: A Tiny Soft Processor Architecture with Multi-Bit Serial Datapaths for FPGAs

作者：Takamaeda Yamazaki Shinya^*; Nakatsuka Hiroshi; Tanaka Yuichiro; Kise Kenji

来源：IEICE TRANSACTIONS ON INFORMATION AND SYSTEMS, 2015, E98D(12): 2150-2158.

DOI：10.1587/transinf.2015PAP0022

• soft processor
• processor architecture
• FPGA

Soft processors are widely used in FPGA-based embedded computing systems. For such purposes, efficiency in resource utilization is as important as high performance. This paper proposes Ultrasmall, a new soft processor architecture for FPGAs. Ultrasmall supports a subset of the MIPS-I instruction set architecture and employs an area efficient microarchitecture to reduce the use of FPGA resources. While supporting the original 32-bit ISA, Ultrasmall uses a 2-bit serial ALU for all of its operations. This approach significantly reduces the resource utilization instead of increasing the performance overheads. In addition to these device-independent optimizations, we applied several device-dependent optimizations for Xilinx Spartan-3E FPGAs using 4-input lookup tables (LUTs). Optimizations using specific primitives aggressively reduce the number of occupied slices. Our evaluation result shows that Ultrasmall occupies only 84% of the previous small soft processor. In addition to the utilized resource reduction, Ultrasmall achieves 2.9 times higher performance than the previous approach.

• 出版日期2015-12