RDCIM: RISC-V Supported Full-Digital Computing-in-Memory Processor With High Energy Efficiency and Low Area Overhead

Digital computing-in-memory (DCIM) that merges computing logic into memory has been proven to be an efficient architecture for accelerating multiply-and-accumulates (MACs). However, low energy efficiency and high area overhead pose a primary restriction for integrating DCIM in re-configurable processors required for multi-functional workloads. To alleviate this dilemma, a novel RISC-V supported full-digital computing-in-memory processor (RDCIM) is designed and fabricated with 55nm CMOS technology. In RDCIM, an adding-on-memory-boundary (AOMB) scheme is adopted to improve the energy efficiency of DCIM. Meanwhile, a multi-precision adaptive accumulator (MPAA) and a serial-parallel conversion supported SRAM buffer (SPBUF) are employed to reduce the area overhead caused by the peripheral circuits and the intermediate buffer for multi-precision support. The results show that the energy efficiency in our design is 16.6 TOPS/W (8-bit) and 66.3 TOPS/W (4-bit). Compared to related works, the proposed RDCIM macro shows a maximum energy efficiency improvement of 1.22x in a continuous computing scenario, an area saving of 1.22x in the accumulator, and an area saving of 3.12x in the input buffer. Moreover, in RDCIM, 5 fine-grained RISC-V extended instructions are designed to dynamically adjust the state of DCIM, reaching 1.2x computation efficiency.