Notes: op, funct, rd, rs, rt, imm, address, shamt refer to fields in the instruction format

PC is assumed to point to the next instruction, Mem is the byte addressed main memory

Common MIPS instructions

Assembly

Instruction

Instr

Format

op/funct

Meaning

Comments

add $rd, $rs, $rt

sub $rd, $rs, $rt

addi $rt, $rs, imm

addu $rd, $rs, $rt R

subu $rd, $rs, $rt

addiu $rt, $rs, imm I

mfc0 $rt, $rd

mult $rs, $rt

multu $rs, $rt

div $rs, $rt

divu $rs, $rt

mfhi $rd

mflo $rd

and $rd, $rs, $rt

or $rd, $rs, $rt

andi $rt, $rs, imm

ori $rt, $rs, imm

sll $rd, $rs, shamt R

srl $rd, $rs, shamt R

lw $rt, imm($rs)

sw $rt, imm($rs)

lbu $rt, imm($rs)

sb $rt, imm($rs)

lui $rt, imm

beq $rs, $rt, imm

bne $rs, $rt, imm

slt $rd, $rs, $rt

slti $rt, $rs, imm

sltu $rd, $rs, $rt

sltiu $rt, $rs, imm

j destination

jal destination

jr $rs

0/32

0/34

0/33

0/35

0/24

0/25

0/26

0/27

0/16

0/18

0/36

0/37

0/0

0/2

0/42

0/43

0/8

$rd = $rs + $rt

Add contents of two registers

$rd = $rs - $rt

Subtract contents of two registers

$rt = $rs + imm

Add signed constant

$rd = $rs + $rt

Unsigned, no overﬂow

$rd = $rs - $rt

Unsigned, no overﬂow

$rt = $rs + imm

Unsigned, no overﬂow

$rt = $rd

rd = coprocessor register (e.g. epc, cause, status)

Hi, Lo = $rs * $rt

64 bit signed product in Hi and Lo

Hi, Lo = $rs * $rt

64 bit unsigned product in Hi and Lo

Lo = $rs / $rt, Hi = $rs mod $rt

Lo = $rs / $rt, Hi = $rs mod $rt (unsigned)

$rd = Hi

$rd = Lo

$rd = $rs & $rt

$rd = $rs | $rt

Get value of Hi

Get value of Lo

Logical AND

Logical OR

$rt = $rs & imm

Logical AND, unsigned constant

$rt = $rs | imm

Logical OR, unsigned constant

$rd = $rs << shamt

Shift left logical (shift in zeros)

$rd = $rs >> shamt

Shift right logical (shift in zeros)

$rt = Mem[$rs + imm]

Load word from memory

Mem[$rs + imm] = $rt

Store word in memory

$rt = Mem[$rs + imm]

Load a single byte, set bits 8-31 of $rt to zero

Mem[$rs + imm] = $rt

$rt = imm * 216

Store byte (bits 0-7 of $rt) in memory

Load constant in bits 16-31 of register $rt

if($rs==$rt) PC = PC + imm (PC always points to next instruction)

if($rs!=$rt) PC = PC + imm (PC always points to next instruction)

if($rs<$rt) $rd = 1; else $rd = 0

if($rs<imm) $rt = 1; else $rt = 0

if($rs<$rt) $rd = 1; else $rd = 0 (unsigned numbers)

PC = address*4

Jump to destination, address = destination/4

$ra = PC; PC = address*4 (Jump and link, address = destination/4)

PC = $rs

Jump to address stored in register $rs

beqz $rs, label

Pseudo

If($rs==0) then goto label See also: bnez, bgez, bgtz, blez, bltz

bge $rs, $rt, label Pseudo

If($rs≥$rt) then goto label See also: bgt, ble, blt (add u for unsigned,eg bgeu)

la $rd, label

Pseudo

$rd = label

Assign the address of the label to register $rd

MIPS Instruction formats

Format

Bits 31-26

Bits 25-21

Bits 20-16

Bits 15-11

Bits 10-6

address

shamt

imm

Bits 5-0

funct

-name

-nr

MIPS registers

usage

stores the value 0, do not write to it!

reserved for assembler

stores function results, more than 2 results (cid:198) stack

function arguments, if more than 4 arguments are needed (cid:198) stack

$zero

$at

$v0 - $v1 2 - 3

$a0 - $a3 4 - 7

$t0 - $t9 8 -15, 24-25 temporary variables

long-living variables

$s0 - $s7 16 - 23

reserved for kernel

$k0 - $k1 26 - 27

points to middle of a 64K block in the data segm.

$gp

stack pointer (top of stack)

$sp

frame pointer (beginning of current frame)

$fp

return address

$ra

writable caller- callee-

saved

yes

internal, not directly accessible, registers

Hi, Lo

status

cause

epc

stores the result of mult/div operations (use mflo, mfhi to access these registers)

contains the address of the next instruction to be fetched

function

code in $v0

arguments

result

operating system functions

print_int

print_float

print_double

print_string

read_int

read_float

read_double

read_string

sbrk

exit

$a0

$f12

$f12/13

$a0 contains the start address of the string

$v0

$f0

$f0/1

$a0 contains the destination address of the

string, $a1 ist maximum length

$a0 contains needed size

string starting at $a0

$v0 contains start address of the memory area

MIPS Assembler Syntax

items:

.data

.word 1, 2

servus:

hello:

.ascii “servus!!”

.asciiz “hello”

.text

.globl main

main:

la $t0, servus

addi $t0, $zero, ‘a’

This is a comment

Store following data in the data segment

This is a label connected to the next address in the

current segment

Stores the values 1 and 2 in next two words

Stores a not terminated string in memory

Stores ‘\0’ terminated string in memory (hello+ \0’)

Note that printing the label servus will give you

the text “servus!!hello”

Store following instructions in the text segment

the label main is the entry point of our program

An instruction connected to a label (e.g. for loops)

assigns the ascii value of ‘a’ to $t0

MIPS Instruction Set Overview