Ch 2. Instructions: Language of the Computer -(8)

5. MIPS Instruction Format & Addressing Modes

Machine Language Structure (MIPS)

• Represent: 0/1 (binary code)
• Length: 32 bits (Design Principle 1)
• Formats: 3 types

R-type Instruction Format

• for arithmetic and logic instructions

• 모든 R-type instruction, op code = 0
• function code: operation 구분(ADD, SUB..)

I-type Instruction Format

• for immediate value(constant value or address)
• LW, SW, ADDI

J-type Instruction Format

• 16bits보다 더 필요
• J, JAL

• PC[31:28] 4bits
  • 고정
• PC[27:2] 26bits
  • 직접 Label이 있는 곳의 위치 언급(주소값)
• PC[1:0]
  • MIPS - byte addressable
  • 1 word = 4 bytes
  • x4 = « 2 (left shift)

Op-code & Function 표

Stored Program Concept

• 폰 노이만 아키텍쳐
• Two Principles
  • Instructions are represented as numbers(0/1)
  • Programs(Instruction sets) are stored in memory
• Memory에서 숫자(0/1)로 되어 있는 Instructions를 한 문장씩 Processor에 가져가 실행

Fetch & Execute Cycle

• Fetch: Memory에서 Processor로 instructions의 이동
  • 정확히는 Processor 안의 Instruction Register(IR)로 이동
• Register 안에 있는 Content에 따라 다음 액션을 control
• 다시 다음 instruction을 fetch (Cycle)
• Control Transfer Instructions
  • control flow 바꿈
  • 실행해야 할 다음 instruction 변경
  • → PC register
    • 다음 instruction이 있는 메모리 위치를 point

LUI

• LUI (Load Upper immediate instruction)
  • Breaking large constants into pieces and then reassemble them into a register

• Ex) 32-bit constant “0x003D 0900”
  • LUI $t0, 0x003D -> t0: 003D 0000
  • ORI $s0, $t0, 0x0900 -> s0: 003D 0900
  • 재조립시 upper part 16bits 판단 방법 (???? 0900)
• Sign Extension
  • Arithmetic
  • addi $s1, $t0, 0x000f -> sign bit = 0, 16bits 모두 0
  • addi $s, $t0, -4 -> sign bit = 1, 16bits 모두 1
• Zero Extension
  • Logic
  • 16bits 모두 0

Pseudo Instruction

• Pseudo instruction
  • 원래 MIPS instruction set 안에는 없는데 assembly language로 쓰면은 마치 있는 것처럼 취급을 해서 action
• Copy
  • Move $t0, $t1
    • = add $t0, $t1, $zero
• Branch if Less Than
  • BLT $t0, $t1, L
  • if ($t0 < $t1) goto L
    • = slt $at, $t0, $t1
      bne $at, $zero, L
• Branch if Greater Than
  • BGT $t0, $t1, L
  • if ($t0 > $t1) goto L
• Branch if Greater (Less) Than or Equal to
  • BGE $t0, $t1, L
  • if ($t0 >= $t1) goto L

MIPS Addressing Modes

1. Immediate addressing
   • addi, andi, slti
   • I-Type
2. Register addressing
   • add, mud, and, slt, sll
   • R-Type
3. Base addressing
   • lw, sw
4. PC-Relative addressing
   • beq, bne
5. Pseudo-direct addressing
   • j, jal
   • direct addressing mode와 비슷하지만 똑같지X

Spim

Pseudo Assembly Instruction

• li $rs, immediatamente: Load immediate value(immed) to $rs
• la $rs, addr: Load address(addr) to $rs

System call (syscall)

• consol window에 출력을 하거나 입력을 받을 때 사용
• 하고 싶은 action을 $v0 register에 load
  • li $v0, 4
  • li $v0, 1
    • 4: print String
    • 1: print Integer
• $a0 ~ $a3: load argument (floating-point: $f12)
  • la $a0, str
  • la $a0, 5