Introduction to RISC-V and the 32I Instruction Set

RISC-V is an open and free instruction set architecture (ISA) that has gained significant popularity in microprocessor design due to its flexibility and efficiency. Unlike proprietary architectures, RISC-V allows developers and researchers to create custom processors without licensing restrictions.

What is RISC-V?

RISC-V is an architecture based on the Reduced Instruction Set Computing (RISC) principle, meaning it uses a simplified instruction set to improve hardware efficiency. It was initially developed at the University of California, Berkeley, and has since been adopted by industry and academia as a viable alternative to proprietary architectures like ARM and x86.

32I Instruction Set

The RISC-V 32I instruction set is the 32-bit basic version with integer instructions. The “I” in its name indicates that it supports general-purpose integer instructions without additional extensions, making it an ideal starting point for educational designs and low-complexity embedded applications. This instruction set is the simplest within the RISC-V family and includes instructions such as:

  • Load and Store: LW, SW (Load Word, Store Word)
  • Arithmetic Operations: ADD, SUB, MUL
  • Branching and Control Flow: JAL, BEQ, BNE
  • Register Manipulation: AND, OR, XOR, SLL, SRL

Being a minimalist instruction set, 32I is suitable for FPGA and low-power ASIC implementations, as in the case of the project documented in this series.

Essential Components for Designing a RISC-V Microprocessor on FPGA

To build a functional RISC-V 32I-based microprocessor from scratch, several essential components are required:

1. Processing Unit (CPU)

  • Implementation of the RISC-V architecture in Verilog or VHDL.
  • Design of the datapath and control unit.

2. Memory

  • RAM for storing instructions and data.
  • Optionally, a ROM or flash for the initial firmware.

3. Input/Output Interface (GPIO)

  • Digital ports for communication with peripherals such as sensors and actuators.

4. Development Tools

  • Synthesis and simulation software (Yosys, Icarus Verilog, Vivado, Quartus).
  • RISC-V GCC compiler to generate binary code.

5. FPGA Platform

  • Tang Nano 20K, Tang Nano 9K, or any compatible FPGA.

In the following articles of this series, we will explore how to implement each of these components step by step, with practical examples and detailed explanations.

This marks the beginning of an exciting technical challenge. Through this series, I will document the design and implementation process of a functional RISC-V 32I microprocessor, aiming to expand its capabilities by integrating GPIO for external device control. Join me on this journey of technological exploration!