CDA 3101

 

1. Loading and Running a MIPS program

A. In your favorite editor , enter the following program. save it as sum.s

The first time that you look at the MIPS code , it looks too complex and difficult to understand, but if you read the explanation about the code you will realize that the code follows the convention of any other well structured Language. After you save the program, go to the following sections to learn the basic instructions of the XSPIM simulator.

An explanation of the code. IMPORTANT!

#------------------------------------------------------------
# sum.s
# Asks for a number i. Then it calculates the sum of all numbers
# from 1 to i
# Register Usage:
# $t0 sum (the sum)
# $t1 i (loop index)
# $t2 testing if i>=1
# $t3 1
# Algorithm in c:
#
# int i,sum;
# scanf ("Please enter a number>=1",&i);
# if (i>=1)
# {
# sum = 0;
# while (i>=1)
# {
# sum = sum + i;
# i = i - 1;
# }
# printf ("The result is: %d", sum);
# }
#-----------------------------------------------------------

            .data
str1:     .asciiz " Please enter a number >= 1 : "
str2:     .asciiz "\n\n The result is:"
            .text
            .globl main

main:
            li $v0, 4                             # Here, we load the value for our macro print_str
            la $a0, str1                        # We pass the argument with the string
            syscall                               # Print the string

            li $v0, 5                             # value for macro read_int
            syscall                               # Get integer
            move $t1, $v0                   # $t1 = $v0

            addi $t3, $zero, 1             # $t3=1
            slti $t2, $t1, 1                   # if $t1<1 then $t2=1 else $t2=0
            beq $t3, $t2, do_nothing  # if $t2==1 do nothing


            addi $t0, $t0, 0               # sum = 0
loop:
            sge $t2, $t1, $t3             # if $t1>=1 then $t2=1 else $t2=0
            beq $t2, $zero, end        # if $t2!=1 exit

            add $t0, $t0 , $t1           # sum = sum + i
            addi $t1, $t1 , -1            # i = i - 1
            j loop

end:
            li $v0, 4                        # Here, we load the value for our macro print_str
            la $a0, str2                   # We pass the argument with the string
            syscall                          # Print the string

            li $v0, 1                        # value for the macro print_int
            move $a0, $t0              # move $t0 to the argument
            syscall

do_nothing:

           li $v0, 10                         #system call code for exit
           syscall                             #executes exit




B. Example of XSPIM window

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C. Load the XSPIM.

In the UNIX shell type the command

xspim &

After that, you will see to appear the previous window.Then in XSPIM, click the "load" button. In the popup dialog box, enter the filename sum.s and click the "assembly file" button. If everything in your program is correct the program should be loaded without problems.

D. Run the program.

Click the "run" button. In the popup dialog box, click "ok". The console window will open and the output of the program will be displayed. You can hide/redisplay the console window with the "terminal" button.
Normally, the code is loaded at the address 0x00400000 , but some times we want to start in another address direction the popup dialog box allows us to change the value for the start position.