RISC-V Operating System-RISC-V ISA Introduction (Part 1)

Reference materials: Chinese manual

Basic introduction to ISA

What is ISA (Instruction Set Architecture)

The Chinese name is instruction set architecture: a layer of interface specification provided by the underlying hardware circuit for the upper-layer software program.

Microarchitecture : The hardware
ISA defines: basic data types, registers, instructions, addressing modes, exceptions and interrupt handling methods.

Why ISA

With ISA, the development of Operating System and Application does not need to consider the hardware part.
IMB 360 The first computer to separate the ISA from its implementation

CISC vs. RISK

• CISC Complex Instruction Set (Complex Instruction Set Computing):
  Implement specific instructions for specific functions, resulting in a large number of instructions, but the generated program is relatively short .
• RSIC Reduced Instruction Set (Reduced Instruction Set Computing):
  Only commonly used instructions are defined, and complex functions are realized through the combination of commonly used instructions, resulting in a relatively small number of instructions, but the length of the generated program is relatively long .
  RISC and CISC tend to merge with each other.

ISA width

The ISA width refers to the width (binary digits) of the general-purpose registers in the CPU. This sentence defines the size of the addressing range and the ability of data operations .

ISA width is independent of instruction encoding length

Well-known ISA Introduction

X86 (complex instruction set), SPARC, Power, ARM, MIPS…