Design and Implementation of Three-stage RISC-V Microprocessor for Education

Abstract

In many computer science and embedded systems courses, processor architecture is typically introduced using either the classical five-stage RISC pipeline or the two-stage AVR pipeline. While these architectures provide a strong introduction to bare-metal programming and computer organization, they do not necessarily represent the most practical or accessible approach for teaching modern processor architectures. In particular, traditional five-stage pipelines often introduce considerable control and forwarding complexity, while compact microcontroller architectures may obscure fundamental pipeline behavior and instruction flow.
This paper presents X3S, a work-in-progress 32-bit pipelined RISC-V softprocessor core originally developed as author’s engineering thesis. The design adopts a simple three-stage pipeline intended to balance architectural clarity, implementation complexity, and achievable operating frequency on Field Programmable Gate Array (FPGA) devices. X3S implements the RV32I base integer instruction set together with the M extension for multiplication and division operations. Multi-cycle arithmetic
accelerators are integrated into the execution pipeline using a handshake-based interface.