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Common Instruction

LB	Load Byte
LBU	Load Byte Unsigned
SB Store	Byte
LH	Load Halfword
LHU	Load Halfword Unsigned
SH	Store Halfword
LW	Load Word
LWU	Load Word Unsigned
SW	Store Word
LD	Load Doubleword
SD	Store Doubleword

MIPS C and Assembly

If/then/else

C Conditional Operator	MIPS Assembly Instruction
a==b	beq $t0,$t1,then
a != b	bne $t0, $t1, then
a < b	blt $t0, $t1, then
a > b	bgt $t0, $t1, then
a⇐b	ble $t0,$t1,then
a>=b	bge $t0,$t1,then
a == 0	beqz $t0, then

Loop

C Loop

Assembly loop

  int i;
  for( i=0;i<10;i++ ) {
     loop body
  }

  int i=0;
  while (i<10){
    loop body
    i++; 
  }

loop.asm

li $t0, 10           #t0 is a constant 10
li $t1,  0           #t1 is our counter (i)
loop:
  beq $t1, $t0, end  #if t1 == 10 we are done
  loop body
  addi $t1, $t1, 1   #add 1 to t1
  j loop             #jump back to the top
end:

strlen example of assembly

string.asm

strlen:
li $t0, 0 #initialize the count to zero
loop:
  lbu $t1, 0($a0) # load the next character into t1
  beqz $t1, exit # check for the null character
  addi $a0, $a0, 1 # increment the string pointer
  addi $t0, $t0, 1 # increment the count
  j loop # return to the top of the loop
exit:

max example of assembly

max.asm

max:
  lw $t0, 0($a0) # load the first array value into t0
  li $t1, 1 # initialize the counter to one
  loop:
    beq $t1, $a1, exit #exit if we reach the end of the array
    addi $a0, $a0, 4 #increment the pointer by one word
    addi $t1, $t1, 1 #increment the loop counter
    lw $t2, 0($a0)   #store the next array value into t2
    ble $t2, $t0, end_if
    move $t0, $t2    #found a new maximum, store it in t0
  end_if:
  j loop             #repeat the loop
exit:

Function call

jal	jump and link	saves the return address (the address of the next instruction, ie $PC + 4) in the dedicated register $ra, before jumping to the function
jr	jump and return	To transfer control back to the caller, the function just has to jump to the address that was stored in $ra

Register Convention

Up to four function arguments can be “passed” by placing them in argument registers $a0-$a3 before calling function via jal
A function can “return” up to two values by placing them in registers $v0-$v1 before returning via jr

The caller is responsible for saving/restoring any of the following caller-saved registers:

$t0-$t9
$a0-$a3
$v0-$v1

The callee is responsible for saving/restoring any of the following callee-saved registers:

$s0-$s7

$ra is special; it is “used” by jal. It is saved by a callee who is also a caller.

Stack frame usage

$sp	stack pointer points to the top of the stack.
$fp	frame pointer ($fp) points to the start of the stack frame and does not move for the duration of the subroutine call. This points to the base of the stack frame, and the parameters that are passed in to the subroutine remain at a constant spot relative to the frame pointer

Push registers $t1 and $t2 onto the stack

stack_push.asm

sub $sp, $sp, 8
sw  $t1, 4($sp)
sw  $t2, 0($sp)
 
An  equivalent  sequence  is:  
sw $t1, -4($sp)
sw $t2, -8($sp)
sub $sp, $sp, 8

Access value in stack frame

lw $s0, 4($sp)

Pop $t1/$t2 from stack frame

addi $sp, $sp, 8

function call example

function_call.asm

_start:         
        #save registers
        sw $t1, -4($sp)
        sw $t2, -8($sp)
        sw $v1, -12($sp)
        sw $v2, -16($sp)
        sub $sp, $sp, 16
 
        #set function parameters
        li $a1, 4  #set function parameters 
 
        #call function/subroutine        
        jal func1
 
        #restore saved registers
        lw $t1, -4($sp)
        lw $t2, -8($sp)
        lw $v1, -12($sp)
        lw $v2, -16($sp)
        addi $sp, $sp, 16
 
        #use return value $v1/v2
        ....
 
 
func1: ....
 
        #prepare returned value in $v1/$v2
        sw $v1, 10
        sw $v1, 100
 
        #return to the caller
        jr $ra

MIPS quick Tutoria	pcspim-tutorial.pdf	TLB	Barrier/Fence/Pipeline Hazards
MipsSimulator

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