[시소실] 2. MIPS ISA(Instruction Set Architecture) (2)

Arithmetic Operations

Arithmetic Operations

• add $s1, $s2, $s3
  : $s1 = $s2 + $s3
• sub $s1, $s2, $s3
  : $s1 = $s2 - $s3

▶ Constant (immediate)

• addi $s1, $s2, 100
  : $s1 = $s2 + 100

 

• mult $s2, $s3
  : HI, LO = $s2 * $s3
• div $s2, $s3
  - LO = $s2 / $s3
  - HI = $s2 % $s3
• mfhi $s1
  : $s1 = HI (Copy the contents of HI to $s1)
• mflo $s1
  : $s1 = LO (Copy the content of LO to $s1)

Cf) HI, LO: Register

 

 

Logic Operations

: 레지스터의 값을 2진수로 바꿔서 논리 연산을 한다.

Logic Operations

• and $s1, $s2, $s3
  : $s1 = $s2 & $s3
• or $s1, $s2, $s3
  : $s1 = $s2 | $s3
• xor $s1, $s2, $s3
  : $s1 = $s2 ^ $s3

▶ Constant (immediate)

• andi $s1, $s2, 100
  : $s1 = $s2 & 100
• ori $s1, $s2, 100
  : $s1 = $s2 | 100

 

 

Data Transfer Instructions

Data Transfer Instructions

▶ Word

• lw $s1, 100($s2) 
  : $s1 Register = (Register $s2의 값 + 100)의 주소를 가지는 Memory 값
• sw $s1, 100($s2)
  : (Register $s2의 값 + 100)의 주소를 가지는 Memory = $s1 Register 값

▶ Byte

• lbu $s1, 100($s2)
  : $s1 = Memory[$s2 + 100]
• sb $s1, 100($s2)
  : Memory[$s2 + 100] = $s1

 

 

MIPS Addressing

• 모든 메모리 접근은 load/store를 통해서만 가능하다.
• 메모리로부터 halfword(2 byte) 또는 byte 단위 load 시,
  - signed operation --> sign-extended
  - unsigned operation --> zero-extended
• Alignment restriction
  - word address: 4의 배수
  - halfword address: 2의 배수

 

 

Conditional Branch Instructions

Conditional Branch Instructions

• beq $s1, $s2, 25(word)
  : if ($s1 == $s2), go to PC+4+100(25 word)
• bnq $s1, $s2, 25
  : if ($s1 != $s2), go to PC+4+100
• slt $s1, $s2, $s3
  : if ($s2 < $s3), $s1 = 1;  else, $s1 = 0;

▶ Constant

• slti $s1, $s2, 100
  : if ($s2 < 100), $s1 = 1;  else, $s1 = 0;

 

 

Unconditional Jump Instructions

Unconditional Jump Instructions

• j 2500(word)
  : go to 10000
• jr $ra
  : go to $ra

---

Opcode Structure

Opcode Structure

 

Base Addressing

• lb $8, 4($9)
  : load byte --> register $8 = memory(4 + $9)

lb $8, 4($9)

 

Register Addressing

• add $8, $17, $18
  : $8 = $17 + $18

add $8, $17, $18

• opcode field = 000000 --> function field가 실제 operation을 결정한다.

 

Immediate Addressing

• addi $8, $9, 4
  : $8 = $9 + 4(byte)

addi $8, $9, 4

▷ immediate: instruction 자체에 직접 포함되는 상수 필드

• 재사용이 불가능하다.
• immediate 필드 용량에는 한계가 있다. (16-bit)
• 추가적 메모리 접근(레지스터 접근)이 없어, 빠른 연산이 가능하다.

 

Jump Instruction

• j next_location(word)
  : jump to the instruction at next_location

j next_location

• jump 에서 next_location은 word(4 byte)로 주어진다.
  --> *4 == 주소 끝에 0을 2개 붙이는 것

 

PC Relative Addressing

• beq $5, $7, XXX
  : if ($5 == $7), jump to XXX

beq $5, $7, XXX

▷ target address = address filed + PC value

• address 필드: 16-bit
• But, program locality(지역성) --> address 필드가 16-bit여도 괜찮다.

 

Branch and Jump

• bne $8, $9, Label(word)
  : if ($8 != $9), jump to Label
• beq $8, $9, Label(word)
  : if ($8 == $9), jump to Label

▷ Address are not always 32-bit.

• branch target address = immediate value + PC
• jump target address = immediate value.