stem/CS/ISA.md

tags
low-level

Instruction Set Architecture

Not Microarchitecture

• Physical implementation of ISA

• Abstract model of a computer

• CPU is an implementation

• Defines

  • Data types
  • Registers
  • Hardware support for main memory
  • Features
    • Memory consistency
    • Addressing modes
    • Virtual memory

• Specifies behaviour of machine code

  • Binary compatibility
  • Allows many implementations

Complexity

Complex

• CISC
  • Complex instruction set computer

Reduced

• RISC
  • Reduced instruction set computer
• Simplifies processor
  • Implementing only frequent instructions
  • Less frequent as subroutines
• Typically requires less transistors than CISC
  • Improves
    • Cost
    • Power consumption
    • Heat dissipation

Very Long Instruction Word

VLIW

Long Instruction Word

LIW

Explicitly Parallel instruction Computing

EPIC

ARM

Acorn RISC Machine Advanced RISC Machines

• RISC architectures
• System-on-Chips, System-on-Modules
  • SOC, SOM
• iPhones A Series
• 32-bit Profiles
  • A
    • Application
    • Cortex-A
  • R
    • Real-time
    • Cortex-R
  • M
    • Micro-controller
    • Cortex-M

Instructions

• Params
  • Registers
    • Functions
      • Arithmetic
      • Addressing
      • Control
  • Memory locations
    • With offsets
  • Addressing modes
    • Interpret operands
• Types
  • Data handling and memory
    • Set register
    • Copy data from memory to register or reverse
      • Load and store operations
    • Read and write from hardware
  • Arithmetic and logic
    • +, -, x, ÷
    • Bitwise
    • Compare
    • Floating point instructions
  • Control flow
    • Branch
      • Another location in program to execute
    • Conditionally branch
    • Indirectly branch
      • Branch with argument memory address
    • Call
      • Save the location to return to
  • Coprocessor
    • Load/store to and from coprocessor
    • Perform coops
  • Complex
    • Multiple things at once
    • Move multiple values between stack and memory
    • Move large blocks of memory
    • Complicated integer and floating point maths
      • Square root, log, sin, cos
    • ALU operations from memory not register