ARMv8 and LEGv8

Notes

• This is H&P chapter 2, Operations of Computer Hardware
  • We will learn the ARMv8 (sort of) assembly/machine language
  • This is going to be strange in some sense
    • We already know an assembly language
    • But this one is different
  • To make it easier, H&P don't study the "pure" ARMv8 machine
  • And there are multiple versions of the ARM architecture.
• ARM - Acorn RISC Machine or Advanced RISC Machines
  • Acorn Computers was a british computer company
  • ARM Holdings was spun off in 1990
• Arms were originaly designed for desktop/personal computers
  • But have been in everything from microcontrolers to supercomputers
  • Their designs are know for low power consumption.
• ARM Holdings does not manufacture chipes,
  • They designs and license technology.
• There are many different versions of the ARM processor
• We are mainly concerned with the ARMv8 - 64
  • We will be programming archimedes.
  • We will be working in 64 bit mode,
  • But this processor can be set to work in 32 bit mode as well
• The ARM Cortex-A72 (The specific processor on Archimedes)
  • Designed to be integrated on a chip with a GPU and other units.
• A small plot twist
  • H&P have made up a machine to simplify study
  • The LEGv8 (that way we have an arm and a leg, intentional)
• This is an idealized version of the ISA
  • A simplified version, so we can get through it without getting lost in the details.
• My intention
  • We will write some ARMv8 assembly code, just for fun.
  • We will use LEGv8 for study.
  • We will try to work out the differences.
• What are the differences?
  • For now, instructions
  • add vs add, addi
  • ARMv8 supports

    
    add rd, rs1, rs2
    add rd, rs1, imm

  • LEGv8 supports

    
    add rd, rs1, rs2
    addi rd, rs1, imm

• Machine Code
  • We have some requirements to work with machine code.
  • We will use the LEGv8 instruction coding scheme.
• Some useful resources
  • The green card a the front of the book
    • You may use this on tests.
  • Pages 64-65 of the book have been helpful in the past.