Homework 4

Homework 4
Student Database - an LC-3 Assembly Language Program

Due on Tuesday, December 4, 2007 at 11:59 pm

Outcomes

After successfully completing this assignment, you will be able to...

Enter, debug, and execute programs written in LC-3 assembly language
Use the LC-3 TRAP instruction to do I/O
Convert integers to ASCII strings
Process an array of records

Before Starting

Read Chapters 6 and 7.

Description of Problem

In this project you'll write a program to process an array of records, where each record contains information about a student's exam scores. For each student in the database, your program will print the student's name, followed by the student's two exam scores, and the calculated average of the exam scores.

Input and Output

The format of each record in the database is as follows: the first item is the name of the student, stored as a zero-terminated ASCII string (one character per word); the second and third items are the student's two exam scores (stored as integers). The database can contain any number of such records, and the last record in the database will be followed by a memory location containing the value x0000. The test scores can take on any value between 0 and #100. The database starts at location x4000.

Given this input:

x4000         'B'
x4001         'e'
x4002         'c'
x4003         'k'
x4004         'e'
x4005         'r'
x4006         x0000
x4007         #94
x4008         #73
x4009         'N'
x400A         'i'
x400B         'c'
x400C         'h'
x400D         'o'
x400E         'l'
x400F         's'
x4010         x0000
x4011         #66
x4012         #53
x4013         x0000

Your program should display this output:

Becker
Exam1:  94  Exam2:  73  Average:  83

Nichols
Exam1:  66  Exam2:  53  Average:  58

The format of your output should look just like the given example.

Hints

This program is more complicated than it might first appear - don't wait until the last minute to do this assignment. Break the program into manageable parts instead of trying to write the whole thing at once. Here is one way you might want to approach this assignment:

Write the code to extract the name of each student. The output from this first version of the program using the sample input would be:
```
Becker
Exam1:  Exam2:  Average:

Nichols
Exam1:  Exam2:  Average:
```
Add the code that will convert the integer scores to ASCII strings, and print them out. The output from this second version of the program would be:
```
Becker
Exam1:  094  Exam2:  073  Average:

Nichols
Exam1:  066  Exam2:  053  Average:
```
You are welcome to make use of the code on page 277 in the text when designing your binary-to-ASCII conversion.
Add the code to get rid of leading zeros. The output from this third version of the program would be:
```
Becker
Exam1:  94  Exam2:  73  Average:

Nichols
Exam1:  66  Exam2:  53  Average:
```
Add the code to calculate and print the exam average (you may use integer division by two to calculate the average; shift the sum of the two exam scores right one bit position).

There are other ways to break up the assignment; the point is to concentrate on one subtask at a time, test it completely, then move on to the next. Comment as you code!

Design Considerations

Make use of subroutines where appropriate. For example, your routine to convert an integer to an ASCII string, and your routine to strip off leading zero's, should both be coded as subroutines.

Documentation Guidelines

You will be using the LC3Edit program to create your assembly language source file. Follow these formatting and documentation guidelines:

The program should contain an introductory comment that includes the programmer's name, login name, and section number, the date, and a brief description of the program. Your description should serve as a general summary of your program's approach to the problem and will also serve as a guideline for assigning partial credit. It is in your best interest to make all of your ideas clear through this summary.
If a register will be used for a specific purpose throughout the program, that register's purpose should be noted in the introductory comments. For example,
```
; Register Usage
; R4 - address of word currently being processed in database
; R5 - holds the sum of the student's exam scores
```
Each field in a line of assembly language source code should be separated by a single tab character. Labels should begin on the left margin (column 1). In the example below, "GetString" begins in column 1, and a tab is placed before "ldr", "r0", and "; R0..."
```
GetString   ldr     r0, r4, #0      ; R0 contains character to be copied
```
Arguments in the operand field should be separated by one space
Either upper- or lower-case characters can be used in assembly language instructions, but be consistent. Choose upper- or lower-case and stick with it.
Main sections of code should be separated by a blank line
Main sections of code should be preceded by a comment, for example
```
; this loop will copy the name of the opponent into StringBuf
```
Comments in the comment field of an instruction should clarify the instruction in the context of the problem being solved. For example, the first comment below is helpful to a reader of the program; the second comment adds no new information or insight:
```
       add   r3, r3, #1     ; point to next location in StringBuf
```
rather than
```
       add   r3, r3, #1     ; add 1 to R3
```

Deliverables

You should turn in two files for this assignment. hw4.asm contains the assembly language code for your program. studentdata.asm contains sample data you used to test your program. Using web-based turnin submit your LC-3 source files before 11:59pm on Tuesday, Dec 4.

Homework 4 Student Database - an LC-3 Assembly Language Program