A 2.41-μW/MHz, 437-PE/mm2 CGRA in 22 nm FD-SOI With RISC-Like Code Generation

Abstract

While coarse-grained reconfigurable arrays (CGRAs) have the potential to improve energy efficiency in general-purpose computing beyond the limitations of von Neumann architectures, they suffer from challenges in code generation. Pasithea-l is a CGRA architecture that aims to combine high energy efficiency with RISC-like programmability. This paper presents its first silicon prototype and a C compiler that uses conventional CPU compiler techniques. Compared to code generation for traditional CGRAs, which require expensive place and route steps, this method of code generation reduces compile times and compiler complexity significantly. Performance and power were measured for a set of benchmark programs written in C. On average, energy efficiency of 195.1 int32 MIPS/mW and active power of 2.41μW/MHz were achieved. Peak energy efficiency of 558.2 MIPS/mW and peak performance of 97.5 MIPS were measured. Load/store instructions and instruction transfers are identified as critical factors for energy efficiency in Pasithea. In comparison to an MCU with state-of-the-art energy efficiency, Pasithea achieves higher energy efficiency in four of the benchmarked programs. Switched capacitance per benchmark run was reduced by a factor of approximately 1.4, on average. Its 0.75 mm2 core area and fabric density of 437 Plis/mm2 enable use in cost-sensitive applications and permit further upscaling.