Week 04 Laboratory Exercises

Objectives

  • learning to run MIPS programs with spim, xspim or qtspim
  • understanding MIPS I/O (syscalls)
  • understanding MIPS control instructions (branch)

Preparation

Before the lab you should re-read the relevant lecture slides and their accompanying examples.

Getting Started

Create a new directory for this lab called lab04, change to this directory, and fetch the provided code for this week by running these commands: 

mkdir lab04
cd lab04
1521 fetch lab04

Or, if you're not working on CSE, you can download the provided code as a zip file or a tar file.

Exercise — in pairs:
Do You MIPS me?

Write a MIPS assembler program bad_pun.s, which is equivalent to this C program: 

// A simple C program that attempts to be punny

#include <stdio.h>

int main(void) {
    printf("I MIPS you!\n");

    return 0;
}

For example:

1521 spim -f bad_pun.s
I MIPS you!

When you think your program is working, you can use autotest to run some simple automated tests: 

1521 autotest bad_pun

When you are finished working on this exercise, you and your lab partner must both submit your work by running give: 

give cs1521 lab04_bad_pun bad_pun.s

Note, even though this is a pair exercise, you both must run give from your own account before Wednesday 01 January 00:00 to obtain the marks for this lab exercise.

Exercise — in pairs:
MIPS Grading

In the files for this lab, you have been given grade.s, a MIPS assembler program which reads a number and always prints FL: 

1521 spim -f grade.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter a mark: 100
FL

Add code to grade.s to make it equivalent to this C program: 

// read a mark and print the corresponding UNSW grade

#include <stdio.h>

int main(void) {
    int mark;

    printf("Enter a mark: ");
    scanf("%d", &mark);

    if (mark < 50) {
        printf("FL\n");
    } else if (mark < 65) {
        printf("PS\n");
    } else if (mark < 75) {
        printf("CR\n");
    } else if (mark < 85) {
        printf("DN\n");
    } else {
        printf("HD\n");
    }

    return 0;
}

For example:

1521 spim -f grade.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter a mark: 42
FL
1521 spim -f grade.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter a mark: 72
CR
1521 spim -f grade.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter a mark: 89
HD

When you think your program is working, you can use autotest to run some simple automated tests: 

1521 autotest grade

When you are finished working on this exercise, you and your lab partner must both submit your work by running give: 

give cs1521 lab04_grade grade.s

Note, even though this is a pair exercise, you both must run give from your own account before Wednesday 01 January 00:00 to obtain the marks for this lab exercise.

Exercise — in pairs:
MIPS Counting

In the files for this lab, you have been given a MIPS assembler program count.s, which reads a number and prints 42: 

1521 spim -f count.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter a number: 13
42

Add code to count.s to make it equivalent to this C program: 

// read a number n and print the integers 1..n one per line

#include <stdio.h>

int main(void) {
    int number, i;

    printf("Enter number: ");
    scanf("%d", &number);

    i = 1;
    while (i <= number) {
        printf("%d\n", i);
        i = i + 1;
    }

    return 0;
}

For example:

1521 spim -f count.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter number: 4
1
2
3
4
1521 spim -f count.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter number: 10
1
2
3
4
5
6
7
8
9
10

When you think your program is working, you can use autotest to run some simple automated tests: 

1521 autotest count

When you are finished working on this exercise, you and your lab partner must both submit your work by running give: 

give cs1521 lab04_count count.s

Note, even though this is a pair exercise, you both must run give from your own account before Wednesday 01 January 00:00 to obtain the marks for this lab exercise.

Exercise — in pairs:
MIPS 7-Eleven

In the files for this lab, you have been given seven_eleven.s, a MIPS assembler program which reads a number and prints 42: 

1521 spim -f seven_eleven.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter a number: 13
42

Add code to seven_eleven.s to make it equivalent to this C program: 

// Read a number and print positive multiples of 7 or 11 < n

#include <stdio.h>

int main(void) {
    int number, i;

    printf("Enter number: ");
    scanf("%d", &number);

    i = 1;
    while (i < number) {
        if (i % 7 == 0 || i % 11 == 0) {
            printf("%d\n", i);
        }
        i = i + 1;
    }

    return 0;
}

For example:

1521 spim -f seven_eleven.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter number: 15
7
11
14
1521 spim -f seven_eleven.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter number: 42
7
11
14
21
22
28
33
35

When you think your program is working, you can use autotest to run some simple automated tests: 

1521 autotest seven_eleven

When you are finished working on this exercise, you and your lab partner must both submit your work by running give: 

give cs1521 lab04_seven_eleven seven_eleven.s

Note, even though this is a pair exercise, you both must run give from your own account before Wednesday 01 January 00:00 to obtain the marks for this lab exercise.

Exercise — in pairs:
MIPS Tetrahedra

In the files for this lab, you have been given tetrahedral.s, a MIPS assembler program that reads a number and prints 42: 

1521 spim -f tetrahedral.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter a number: 42
42

Add code to tetrahedral.s to make it equivalent to this C program: 

// Read a number n and print the first n tetrahedral numbers
// https://en.wikipedia.org/wiki/Tetrahedral_number

#include <stdio.h>

int main(void) {
    int i, j, n, total, how_many;

    printf("Enter how many: ");
    scanf("%d", &how_many);

    n = 1;

    while (n <= how_many) {
        total = 0;
        j = 1;

        while (j <= n) {
            i = 1;
            while (i <= j) {
                total = total + i;
                i = i + 1;
            }
            j = j + 1;
        }
        printf("%d\n", total);
        n = n + 1;
    }
    return 0;
}

For example:

1521 spim -f tetrahedral.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter number: 5
1
4
10
20
35
1521 spim -f tetrahedral.s
Loaded: /home/cs1521/share/spim/exceptions.s
Enter number: 12
1
4
10
20
35
56
84
120
165
220
286
364

When you think your program is working, you can use autotest to run some simple automated tests: 

1521 autotest tetrahedral

When you are finished working on this exercise, you and your lab partner must both submit your work by running give: 

give cs1521 lab04_tetrahedral tetrahedral.s

Note, even though this is a pair exercise, you both must run give from your own account before Wednesday 01 January 00:00 to obtain the marks for this lab exercise.

Challenge Exercise — individual:
Read & Execute MIPS Instructions

Write a MIPS assembler program dynamic_load.s which reads MIPS instructions as signed decimal integers until it reads the value -1, then executes the instructions.

dynamic_load.s should read instructions until it reads the value -1.

dynamic_load.s should then print a message, load the instructions, print another message, exactly as in the examples below.

For example, below is a tiny MIPS assembler program which prints 42. The comment on each line shows how the instruction is encoded, as a hexadecimal and as a signed decimal integer; it is this signed integer value that your program will read. 

li $a0, 42  # 3404002a  -3422289878
li $v0, 1   # 34020001  -3422420991
syscall     # 0000000c           12
jr $ra      # 03e00008     65011720

This is what dynamic_load.s must do.

1521 spim -f dynamic_load.s
Enter mips instructions as integers, -1 to finish:
-3422289878
-3422420991
12
65011720
-1
Starting executing instructions
42Finished executing instructions

The supplied files for the lab include files containing the instructions for some MIPS assembler programs from lectures. You can use these to test your program; for example: 

cat add.instructions
-3422027759
-3421962215
19419168
663585
-3422420991
12
-3422289910
-3422420981
12
65011720
-1
1521 spim -f dynamic_load.s <add.instructions
Loaded: /home/cs1521/share/spim/exceptions.s
Enter mips instructions as integers, -1 to finish:
Starting executing instructions
42
Finished executing instructions
1521 spim -f dynamic_load.s <print10.instructions
Loaded: /home/cs1521/share/spim/exceptions.s
Enter mips instructions as integers, -1 to finish:
Starting executing instructions
1
2
3
4
5
6
7
8
9
10
Finished executing instructions
1521 spim -f dynamic_load.s <sum_100_squares.instructions
Loaded: /home/cs1521/share/spim/exceptions.s
Enter mips instructions as integers, -1 to finish:
Starting executing instructions
338350
Finished executing instructions

If you want to experiment with your own tests, this command will give you any MIPS program as integers. 

1521 mips_instructions 42.s
-3422289878
-3422420991
12
65011720
-1

If you want to try creating your own test cases, here is some MIPS assembler that prints a message without using initialized data: 

# print a string without using pre-initialized data
# for the dynamic load challenge exercise

main:
    li   $a0, 'H'       # printf("%c", 'Hi');
    li   $v0, 11
    syscall
    
    li   $a0, 'i'       # printf("%c", 'i');
    li   $v0, 11
    syscall
    
    li   $a0, '\n'      # printf("%c", '\n');
    li   $v0, 11
    syscall

    jr $ra

When you think your program is working, you can use autotest to run some simple automated tests: 

1521 autotest dynamic_load

When you are finished working on this exercise, you must submit your work by running give: 

give cs1521 lab04_dynamic_load dynamic_load.s

You must run give before Wednesday 01 January 00:00 to obtain the marks for this lab exercise. Note that this is an individual exercise, the work you submit with give must be entirely your own.

Submission

When you are finished each exercises make sure you submit your work by running give.

You can run give multiple times. Only your last submission will be marked.

Don't submit any exercises you haven't attempted.

If you are working at home, you may find it more convenient to upload your work via give's web interface.

Remember you have until Wednesday 01 January 00:00 to submit your work.

You cannot obtain marks by e-mailing your code to tutors or lecturers.

You check the files you have submitted here.

Automarking will be run by the lecturer several days after the submission deadline, using test cases different to those autotest runs for you. (Hint: do your own testing as well as runningautotest.)

After automarking is run by the lecturer you can view your results here. The resulting mark will also be available via give's web interface.

Lab Marks

When all components of a lab are automarked you should be able to view the the marks via give's web interface or by running this command on a CSE machine: 

1521 classrun -sturec