Lab 06: MIPS Programming

Lab 06: MIPS Programming
CSE-031-01

Overview
In this lab, we will continue to familiarize ourselves with programming MIPS using MARS. We will focus on
memory accesses and control flow.
Getting Started
Before we begin any activities, create a directory (Lab_6) inside the CSE31 directory we created in the first
lab. You will save all your work from this lab here. Note that all the files shown in green below are the
ones you will be submitting for this assignment.
You must have a clear idea of how to answer the lab activities before leaving lab to receive
participation score.
Memory in MARS?
MARS not only simulates a MIPS CPU, it also simulates the memory so the CPU can work with it. We will
revisit fib.s from Lab 05 in this exercise. Load fib.s into MARS and assemble the code.
TPS (Think-Pair-Share) activity 1: Discuss questions 1 – 12 (25 minutes) while paired with your
classmates assigned by your TA (you will be assigned to groups of 3-4 students) and record your answers in
a text file named tpsAnswers.txt under a section labelled “TPS 1” (you will continue to use this file
to record your answers to all the TPS questions that follow in the lab handout):
1. Once fib.s is assembled, open the Execute tab (it should be opened by default after assembled). Two
segments of memory are displayed here: Text Segment and Data Segment. What are the starting
addresses of Text Segment and Data Segment? Give your answers in Hex format.
2. The Text Segment shows you how each actual machine code is stored in the memory (again it is
simulated) and its corresponding MIPS code. Two types of MIPS code are shown here: Basic and Source.
We call the Basic one True Assembly Language, and the Source one MIPS Assembly Language.
From the display, what can you tell about the difference between the two in terms of their relationship
with the machine code? We will cove this topic in future lectures.
3. Now, let us take a look at the Data Segment. How much difference in bytes are there between 2 address
locations (again, the addresses are in Hex)?
4. For each address location, how many columns are there?
5. What can you tell about the relationship between the address difference and the number of columns at
each address location?
6. From the source code, how do you create a new variable/label named m and set it to 20?
7. Save and assemble your file. At what address is the value of m stored?
8. Besides numbers, we can also initialize strings for the program to use. Search from the Internet on how
to declare a string named str1 and set it to “I love CSE31!”
9. Insert the declaration of str1 in your code and assemble it. From the Data Segment, we can see that
the string is occupying 3 address locations. At what addresses is str1 stored?
10. str1 is stored as numerical values in the memory. Check the ASCII box and observe how it is stored.
Does the display of characters agree with what you have learned from Lab 04 about how an array of
characters is stored?
11. In order to print str1, we will need to use syscall function. Search the Internet to find out how to
print str1.
12. Now let us go back to the program. Search from the Internet to find out what “la $t3, n” does.
What will be the value stored in $t3 after running this instruction? From this we can see that we cannot
Lab 06: MIPS Programming
CSE-031-01 Points: 20
use the initialized variables (labels) directly in our MIPS program. We need to use la, then lw to save
the value into a register
Your TA will “invite” one of you randomly after the activity to share what you have discussed.
Create compare.s
Write a new piece of MIPS program named compare.s and complete the following exercise.
TPS activity 2: Discuss questions 1 – 8 (25 minutes) with your TPS partners in your assigned group and
record your answers in tpsAnswers.txt under a section labelled “TPS 2”:
1. From lectures, we have learned that we can perform different inequality comparisons (<, >, <=, >=) by
using only slt, beq, and bne instructions. Why not having one instruction for each inequality in
MIPS?
2. Declare a new variable/label (n) and set it to 25.
3. Insert instructions to declare the following strings:
a. str1: "Less than\n"
b. str2: "Less than or equal to\n"
c. str3: "Greater than\n"
d. str4: "Greater than or equal to\n"
4. Insert instructions to read in an integer from users. Search from the Internet on how to use syscall to
do it.
5. Insert code so the program will compare if the user input is less than n. If it is, output “Less than”.
6. Insert code so the program will compare if the user input is greater than or equal to n. If it is, output
“Greater than or equal to”.
7. Now comment out your code from steps 5 and 6. Insert code so the program will compare if the user
input is greater than n. If it is, output “Greater than”.
8. Insert code so the program will compare if the user input is less than or equal to n. If it is, output “Less
than or equal to”.
Individual Assignment 1: Create sumAll.s
Create a new MIPS program that will ask a user to enter a number repeatedly. This program will calculate 2
sums: even_sum (sum of all even numbers) and odd_sum (sum of all odd numbers). The program will
stop when the user enters a ‘0’ and print out both sums (even if they are zero).
You may NOT use any the following instructions in your solution: div, and, or, andi, or ori.
You will be using a loop to determine when to end the program. In MIPS, ALL types of loop can be
implemented with a branch statement (beq or bne). Therefore, write a pseudocode to describe your
approach to this problem before writing the MIPS code. It is VERY SIMILAR to the average.c you
created in Lab 01.
Save your code as sumAll.s.
Sample Run (user input shown in blue, with each run separated by a dashed line):
-------------------------------------------------------------------------------SAMPLE RUN 1
Please enter a number: 1
Please enter a number: 2
Please enter a number: 3
Please enter a number: -1
Please enter a number: -2
Please enter a number: -3
Please enter a number: 0
Sum of even numbers is: 0
Sum of odd numbers is: 0
-------------------------------------------------------------------------------SAMPLE RUN 2
Please enter a number: 1
Please enter a number: 2
Please enter a number: 3
Please enter a number: -7
Please enter a number: -8
Please enter a number: 0
Sum of even numbers is: -6
Sum of odd numbers is: -3
Collaboration
You must credit anyone you worked with in any of the following three different ways:
1. Given help to
2. Gotten help from
3. Collaborated with and worked together
What to hand in
When you are done with this lab assignment, submit all your work through CatCourses.
Before you submit, make sure you have done the following:
• Attached compare.s, sumAll.s and tpsAnswers.txt.
• Filled in your collaborator’s name (if any) in the “Comments…” textbox at the submission page.
Also, remember to demonstrate your code to the TA or instructor before the end of the grace period.