CS641 MIPS Instruction Formats

Ref: green card at front of book, plus table on pg. 78 (some more on pg. 281), B.10

NOTES

Pseudo-Instructions we have used: move, li, la, b, bge, bgt, ble, blt

Another real instruction we’ve used: syscall

Floating point: don’t worry about instruction formats (similar)

Note: ignore trailing “u” on an instruction for now: determines trap behavior on errors

R-Format Instructions: add, and, jr, nor, or, slt, sll, srl, sub

0 for shifts only

add $8,$9,$10

opcode = 0 (look up in table in book)

funct = 32 (look up in table in book)

rs = 9 (first operand)

rt = 10 (second operand)

rd = 8 (destination)

shamt = 0 (not a shift)

Called a Machine Language Instruction:

hex representation: 012A 4020_hex

I-Format Instructions: addi, andi, ori, slti, lb, lui, lw, sb, sw, branches

addi $21,$22,-50

opcode = 8 (look up in table in book)

rs = 22 (register containing operand)

rt = 21 (target register)

immediate = -50 (by default, this is decimal in assembler code)

Branches: PC-Relative Addressing: beq, bne

Use I-Format

If we do take the branch (else PC = PC + 4):

PC = (PC + 4) + (immediate * 4)

J-Format Instructions: for jumping further: j, jal (jr is R format)

° New PC = { PC+4[31..28], address, 2’b0 } from green card in book