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CSE/EEE 230 Computer Organization and Assembly Language
Homework 2 :: 50 pts
1 Instructions
You may work in pairs with a partner on this assignment if you wish or you may work alone. If you work with a partner,
only submit one zip archive with both of your names in the PDF document and source code file; you will each earn the
same number of points. Your zip archive must be uploaded to Blackboard by the assignment deadline. Section 3 describes
what to submit and by when.
2 Exercises
1.
A MIPS word is stored at memory address 0x1000_100A. Is this word naturally aligned? If so, explain why, and if
not, explain why not.
2.
Consider this C code. Assume the values of variables e, f, g, and h have been loaded from memory into registers $t0,
$t1, $t2, and $t3, respectively. Assume we are associating variable i with register $s0. Write the MIPS instructions—
not a complete program—that implements the assignment statement.
int e, f, g, h, i;
i = e * (f + g - h);
3.
(a) Explain why we cannot write addi $t0, $zero, 65536 to load the immediate 65,536 into $t0. (b) Write a single
lui instruction that loads the immediate 65,536 into $t0.
4.
Many processor ISA's have instructions which rotate the bits of a word left or right. During a rotate left operation,
bits that would normally be lost during a shift left are instead rotated into the least significant bits. For example,
suppose $t0 contains 0x9122_3344 and we rotate $t0 left n bit positions,
$t0 before rotate left:
$t0 after rotate left 1 bit position:
1001 0001 0010 0010 0011 0011 0100 0100
0010 0010 0100 0100 0110 0110 1000 1001
$t0 before rotate left:
1001 0001 0010 0010 0011 0011 0100 0100
$t0 after rotate left 7 bit positions: 1001 0001 0001 1001 1010 0010 0100 1000
A rotate right works similarly, except bits that would normally be lost during a shift right are rotated into the most
significant bits. MIPS does not have rotate left or rotate right instructions. However, they can be implemented as
pseudoinstructions. For this exercise, write the MIPS physical instruction sequence which would implement a pseudo instruction rotl1 $dst, $src (rotate left by 1) that rotates the bits in $src one position to the left and writes the
result to $dst. You are only allowed to use three registers in your code: $src, $dst, and $at; $src shall not be modified.
Note, $src and $dst are not real MIPS registers, but rather, are placeholders for the registers that are actually used
when writing the rotl1 instruction. For example, if the programmer writes rotl $t0, $t1 then $src is $t1 and $dst
is $t0. I'll give you a hint, these are your instructions, which I wrote in this order: lui, and, srl, sll, or.
5.
Write MIPS assembly language code that would define and initialize these variables in the .data section.
int e = 0 , f = 10, g = -1;
char ch = ' ';
char char_array[128] = { '\0' };
int int_array1[100] = { 0 };
int int_array2[3] = { 1, 2, 3 };
6.
Write assembly language instructions—not a complete program—that: (1) loads $t1 with the immediate 0x1C59; (2)
loads $t2 with the immediate 0x3687; (3) performs a logical AND of $t1 and $t2 and writes the result to $s0; (4)
performs a logical OR of $t1 and $t2 and writes the result to $s1; (5) performs a logical XOR of $t1 and $t2 and
writes the result to $s2; (6) performs a logical NOR of $t1 and $t2 and writes the result to $s3.
7.
Continuing, for each of the four logical instructions (and, or, xor, and nor) what value would be written to the
destination registers? Write your answer as a 8-hexdigit number.
(c) Kevin R. Burger :: Computer Science & Engineering :: Arizona State University
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CSE/EEE 230 Computer Organization and Assembly Language
8.
Homework 2 :: 50 pts
Name your source code file hw02-8.s. Write a complete MIPS assembly language program that implements this
pseudocode:
Define global integer variables a = 0, b = 0, c = 0 (in the .data section)
Program hw02-6
SysPrintStr("Enter a: ")
a = SysReadInt()
SysPrintStr("Enter b: ")
b = SysReadInt()
c = 2a3 + b2 - 1
SysPrintStr("2a^3 + b^2 - 1 = ")
SysPrintInt(c)
SysExit()
End Program
Miscellaneous program requirements and hints:
a. Write the code so its behavior would match this sample output, where sample user input is in bold:
Enter a: 7
Enter b: -5
2a^3 + b^2 - 1 = 710
b. The information on the MARS system calls can be found by selecting Help | Help on the main menu (or hit F1).
In the Help window click on the Syscalls tab. Information on MARS-implemented MIPS32 instructions can be
found by clicking on the Basic Instructions and Extended (pseudo) Instructions tabs. Information on MARSimplemented assembler directives can be found by clicking on the Directives tab. For this program you will need
to use the following directives: .data for the data section; .text for the text section; .word for the definitions of
integer variables a, b, and c; asciiz to place the string literals in the data section.
b. Define a, b, and c as global variables in the .data section using the .word directive. Initialize them to 0.
c. Place the strings in the .data section using the .asciiz directive.
e. For my solution, I used these MIPS32 instructions, so familiarize yourself with them: add (add signed); addi (add
immediate signed); la (load address); li (load immediate); lw (load word); mul (multiply); sll (shift logical left,
used to quickly multiply a3 by 2); sw (store word); and syscall (make a system call).
f. Study the assembly language source code files from the course notes and posted on the course website. Format
your code in a similar manner, i.e., most assembly language source code lines consist of four columns of text:
column 1 is left aligned with the margin and is reserved for an optional label; column 2 is indented and is reserved
for instruction mnemonics; column 3 is indented and reserved for optional operands; column four is indented and
is reserved for comments. How many spaces or tabs you indent is up to you, the important thing is to line things
up in columns and be consistent.
g. You are required to write a comment in column 4 for each instruction. This may seem like busy work, but it can
be very helpful when your code does not work and you are trying to figure out why. Trust me on this one.
h. Even though this code could be optimized (e.g., we don't really need to allocate the variables a, b, and c in the
data section because we have enough registers to store all of the values) I don't want you to optimize it. What I
mean is, when you read the integer value for a, store the value that was entered in the memory location allocated
to a. Later, when you need to value of a again, load it from the memory location allocated to a. Perform the same
operations for b and c. There is merit in learning how to do something the hard way before seeing how to do it the
easy way. Unoptimized, my solution required 32 instructions (38 if we count the actual number of physical
instructions that were generated after pseudoinstructions were expanded).
i. Make sure to properly terminate the program by making a syscall to SysExit().
j. Write a header comment block at the top of the source code file in the format shown on the next page. Make sure
to put both author's names in the header comment block if you worked with a partner.
(c) Kevin R. Burger :: Computer Science & Engineering :: Arizona State University
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CSE/EEE 230 Computer Organization and Assembly Language
Homework 2 :: 50 pts
#*******************************************************************************
# FILE: hw02-8.s
#
# DESCRIPTION
# Asks the user to enter two integers a and b. The program calculates and
# displays 2a^3 + b^2 - 1.
#
# AUTHOR INFO
# your-name (your-email-addr)
# your-partners-name (your-partners-email-addr)
#*******************************************************************************
3 Submission Instructions
Type your answers to Exercises 1–7 in a document and convert the document to PDF. If you work with a partner, be
sure to put both of your names in the document. To convert your document into PDF format, Microsoft Office versions
2008 and newer will export the document into PDF format by selecting the proper menu item from the File menu. The
same is true of Open Office and Libre Office.
THERE WILL BE A 25% PENALTY FOR NOT SUBMITTING YOUR SOLUTION IN PDF FORMAT.
FURTHERMORE, IF YOU SUBMIT A DOCUMENT WHICH IS NOT IN PDF FORMAT AND THE
GRADER CANNOT OPEN THE DOCUMENT BECAUSE IT IS IN SOME WEIRD FORMAT, YOU
WILL BE GIVEN A SCORE OF 0 ON EXERCISES 1–7.
Then, create an empty folder named 230-s15-h02-asurite where asurite is your ASURITE user name (this is not your
ASU id number, e.g., mine is kburger2). If you worked with a partner, name the folder 230-s15-h02-asurite1-asurite2
where asurite1 and asurite2 are the ASURITE user names of both partners. Copy the PDF document and your hw02-8.s
source code file to this folder. Next, create a zip archive of the folder naming the zip archive 230-s15-h02-asurite.zip or
230-s15-h02-asurite1-asurite2.zip.
Upload the zip archive to Blackboard using the homework submission link by the deadline which is 4:00am Mon 9 Feb
(Note: this is four o'clock in the morning on Monday, which for some of you, will be very late Sunday night). Consult the
online syllabus for the late and academic integrity policies.
(c) Kevin R. Burger :: Computer Science & Engineering :: Arizona State University
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