CSE 378 - Autumn 2005

Machine Organization and Assembly Language Programming

Programming Assignment #0. Familiarization with SPIM

Not to be turned in BUT PLEASE DO IT

The purpose of this homework is to familiarize you with the R3000 Simulator, spim. In this assignment you will learn how to use spim to run assembly language programs and to extract information to debug your programs. In doing this, you will use a program that is already written in assembly language. Since many operations in assembly language are similar to those in high-level languages, you might be able to understand some of what the program is doing. But don't worry if you don't understand all of it now. You will learn assembly operations later on as we discuss them in class and in sections, and as you read Appendix A and Chapter 3. The purpose of this assignment is simply for you to become familiar with the spim environment.

Note: This software is already installed on the Windows machines in the labs at O:\cse\courses\cse378\spim\SPIM63a\bin. Don't make 65 copies of it on the CSE servers -- if you can, use this already-installed version. It is small and self-contained, so you should be able to use it on home machines as well. Currently we are only supporting the PC version. If you want to download SPIM on your personal computer, or cannot access it in the labs, you can find everything you need on the on the Software link of the home page or directly at SPIM

For this assignment, we will use a program that computes the 10th Fibonacci number. The C version appears in Listing 1, and the MIPS Assembly version in Listing 2.

You can download the (unnumbered) assembly code from here. Simply click on the link and save it someplace you can remember. You then want to "Open" it using PCSpim.

I.  Execute the program in the simulator. Use "Go" (F5 is a shortcut) in the simulator menu and the start address 0x00400000 (this can be done in the dialog box that will open under the GO command). What is printed on the spim console?

Now run the program in single steps (F10 is the keyboard shortcut) When you want to re-run the program, you will have to "reload" to make it work!!. In order to set the PC use "Set Value" in the simulator menu with the register name being PC, and the value 0x00400000. You can verify it is correct by looking at the value of the PC displayed as the top lefmost register. Do you notice any discrepancies between the given program and the instructions executed by spim? What are a few (3 - 5) of the discrepancies?

II. Complete the following table by examining various registers and memory location contents after executing the appropriate instructions. Try to use the breakpoint command. If you are seeing strange things, think about "reloading" the program within spim.

Location	Line 16	Line 26 first iteration	Line 26 fourth iteration	Line 38
$25
$24
$8
8($sp)
4($sp)

---

Listing 1 (C Code):

 
#include <stdio.h>
 
main() {
 int i = 3; 
 int fib1 = 1; 
 int fib2 = 1;
 int temp; 
 
 for(i; i <= 10; i++) { 
 temp = fib1 + fib2; 
 fib2 = fib1; 
 fib1 = temp; 
 }
 
 printf("The 10th fibonacci number is: %d\n", fib1); 
}

Listing 2 (Assembly Code):

 
 1: .data # Tells assembler that this is data
 2: message: 
 3: .asciiz "The 10th fibonacci number is: "
 4: newline: 
 5: .asciiz "\n"
 6: 
 7: .text   # Tells the assembler that the following is code
 8: .globl main # Entry into our code must be global
 9: 
10: main: 
11: subu $sp, 12 # Allocate 3 words of storage space on stack
12: sw $31, 0($sp) # Save the return address (to caller of main)
13: 
14: li $14, 1 # Put a constant 1 into temporary register 14
15: sw $14, 4($sp) # Put a 1 into our two words of temporary storage
16: sw $14, 8($sp) # Stores c-equivalent of fib1 and fib2
17: 
18: li $8, 3 # Our iteration counter starts at 3 because
19:  # the first two numbers are one (loaded above)
20: 
21: loop:  # Label denoting a position of code named "loop"
22: lw $24, 4($sp) # Put fib1 into register 24
23: lw $25, 8($sp) # Put fib2 into register 25
24: addu $25, $25, $24 # Put next fibonacci number into register 25
25: sw $24, 8($sp) # Put fib1 into storage reserved for fib2
26: sw $25, 4($sp) # Put the new fibonacci number into fib1
27: addu $8, $8, 1 # Increment the counter
28: ble $8, 10, loop # If counter $8 <= 10, go to loop
29: 
30:  # fib1 [4($sp)] now has our 10th fibonacci number
31: 
32: li $2, 4 # Use syscall 4 (print_string)
33: la $4, message # Load address of string "message" in .data section
34: syscall  # Print the message
35:  
36: li $2, 1 # Use syscall 1 (print_int)
37: lw $4, 4($sp) # Load the number 
38: syscall # Print the number
39: 
40: li $2, 4
41: la $4, newline
42: syscall
43: 
44: lw $31, 0($sp) # Get return address
45: addu $sp, 12 # Restore stack pointer
46: j $31 # Return to caller
47: 
48: .end main