Question

Given:  MIPS Programming in MIPS Assembly Language

Assume: Load, Store, R-format, and Jump (j) instructions have CPI = 1

Assume: Branch and jr or ja Instructions (e.g., branches) have CPI = 2

Assume: All MIPS system calls (e.g., for printing) have CPI = 3

Assume: Variable x stored in register $s1, y in $s2, z in $s3, i in $t0

Express the following precondition loop in MIPS assembly language

              x := 0 ; i := 5 ;         # Document each MIPS statement
              while (x < 10) do:
              {  x := x + 2 ; i := i - 1}
              syscall(print, "Did ", i , " iterations")

How many cycles are used by your MIPS program?  

(I would really appreciate it if you could explain how you found the number of cycles)

Answer 1

.data
msg1 : .asciiz "Did "
msg2 : .asciiz " iterations"
x : .word 0
i : .word 5
   .text
   .globl main
main:
#load instructions are lw,li,la takes 1 cycle
#R-format instructions are addi,add,sub
#branch instructions are blt takes 2 cycles
#system calls takes 3 cycles   

#$s1 : store the x
#$t0 : store the i

lw $s1,x #lw - load word.copy x to $s1 #1cycle

lw $t0,i #lw - load word.copy i to $t0 #1cycle
# $v0 = 4. print the string
# $v0 = 1. print the integer
# $v0 = 10 .Exit the program

#This loop takes 4 cycles for 1 iteration
#So for 5 iterations it take 20 cycles
#while loop
loop:
#x = x + 10
addi $s1,$s1,2 #add immediate $s1 and 2.Result will store in $s1 # 1cycle
#i = i - 1
sub $t0,$t0,1 #subtract $t0 and 1.Result will store in $t0 # 1cycle
#if(x<10)
blt $s1,10,loop #branch if less than.If $s2 less than 10 ,jump to label loop # 2cycles
  
#print the msg1.This print takes 1+1+3 = 5cycles
li $v0,4 #print string syscall code is 4 # 1cycle
la $a0,msg1 #load the address of msg1 # 1cycle
syscall # 3 cycles

#syscall to print integer
#print the i value..This print takes 1+1+3 = 5cycles
li $v0,1 #print integer syscall code is 1 # 1cycle
move $a0,$t0 #copy value of $s2 to $a0 # 1cycle
syscall                     #3 cycles
#print the msg2.This print takes 1+1+3 = 5cycles
li $v0,4 #print string syscall code is 4 # 1cycle
la $a0,msg2 #load the address of msg1 # 1cycle
syscall                       #3 cycles

#Termination takes 1+3 = 4cycles
li $v0,10 #$v0 == 10 terminate the program # 1cycle
syscall #executes the above operation #3 cycles

#So totally this program takes 41 cycles