Novel Toolset for Efficient Hardwired Micro-Op Translation in Embedded Microarchitectures

Modern SoCs require increasingly complex embedded control deep within their numerous sub-blocks without adding significant die area. This motivated the creation of $\mu $ RTL, a novel toolset for systematically designing efficient pipelined implementations of embedded instruction sets originally intended for multicycle execution. $\mu $ RTL utilizes hardwired micro-op translation, a technique commonly used in the instruction decoders of large super-scalar microprocessors, however this technique has been overlooked for designing smaller, more efficient embedded microprocessors. Furthermore, the tools to develop instruction decoders with micro-op translation are proprietary and the techniques are trade secrets. The $\mu $ RTL toolset is open-source and this letter clearly presents the methodology. The methodology emphasizes direct opcode decoding from multiple synthesized Verilog blocks versus traditional microprogramming which uses sequential decoding from a ROM. Our results show that a pipelined $\mu $ RTL microarchitecture achieves a 21.8% reduction in size compared to a hardwired multicycle implementation of the same instruction set. Additionally, the performance of 0.75 DMIPS/MHz surpasses the RISC-V PicoRV32 by 44.2% and the AVR RISC by 82.9%. These improvements in performance, power, and area are of interest to embedded system architects.