CS1021 Assignment #1 Simple Statistics Calculator


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In this assignment, you will develop a program to compute a number of statistical measures
(count, sum, min, max, mean) for a sequence of sample values. You will develop the program in
three stages.

In Stage 1, you will write a program that can read a single unsigned value entered
by a user. In Stage 2, you will extend your program to read a sequence of values and compute
the statistical measures. Finally, in Stage 3, you will extend your program further to display the
mean of the sequence of values on the screen.
Important Note: You must submit your solution to each stage of the assignment as a separate .s
ARM Assembly Language source file. Stages 2 and 3 build on Stages 1 and 2 respectively, so you
should begin these stages using your solution from the preceding stage as a starting point.
1 Console Input
The aim of this stage of the assignment is to design, write and test an ARM Assembly Language
program that will read an unsigned value entered by a user in decimal form and store the value in
register R4. The value will be entered by the user as a string of ASCII characters. For example,
if a user enters “2”, followed by “1”, followed by “3”, your program should store 21310 (i.e.
110101012 or D5 16) in R4.
The ConsoleInput µVision project contains a simple program that demonstrates how to read
ASCII characters from the console one character at a time, as they are entered by a user. A
single character is read by executing the BL getkey instruction. This instruction only completes
execution when the user presses a key. When the instruction completes, the ASCII character code
corresponding to the key pressed will be stored in R0.
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School of Computer Science and Statistics
CS1021 / Introduction to Computing I
The key pressed by the user is not automatically displayed in the console window so we need
to do this ourselves with the BL sendchar instruction. This instruction displays the character
corresponding to the ASCII code contained in R0.
Example: If we execute BL getkey and the user types ’7’ on the keyboard, then 0x37 will be
stored in R0. If we then execute BL sendchar (with 0x37 in R0) then ’7’ will be displayed on
the console.)
Very Important Note: Executing the BL getkey or BL sendchar instructions may overwrite
the contents of R0–R3 so you should avoid using these registers to store any values that you
will need after executing either of these instructions. You must also avoid using R13–R15, as
The program should stop reading ASCII characters when the ASCII Carriage Return character
is read. This should occur when the user presses the RETURN key. The Carriage Return
character has ASCII code 0x0D.
Verify that your program stores the value entered in R4.
Using the µVision Console
The program above requires you to enter text using a “console”. To simplify this, you should only
test your program in Simulation mode, which simulates the ARM hardware. (Using a “console”
with the real ARM hardware is slightly more complicated. By using the simulator, you will also
be able to work on the assignment on your own computer.)
To open the console window in Debug mode, select the View – Serial Windows – UART #1
menu option.
When testing your program, you can either step through the program one instruction at a time or
use the run icon to run the program without stopping. If you are stepping through one instruction
at a time, after executing BL getkey you will need to mouse-click in the “UART #1” console
window and press a single key. Your program will then continue to the next instruction.
As always, it is highly recommended that you use uVision version 4 and not version 5 for this
project as it greatly simplifies the process of stepping through your programs one instruction at
a time.
Alternatively, if you choose to run the whole program, you can mouse-click inside the console
window and enter the full expression. To see the result of your program in R4, you will need to
halt your program with the Halt icon (beside Run).
2 Sample Sequence and Statistic Computation
In this Stage of development, you will extend your program to read a sequence of values and
compute the following statistical measures:
• Count
• Sum
• Min
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School of Computer Science and Statistics
CS1021 / Introduction to Computing I
• Max
• Mean
Your program should store each result in a separate register.
Your solution should be an extension of the program that you developed for Stage 1. You should
use the StatEval µVision project to develop and thoroughly test your solution.
You may assume when writing your program that the user will be “well behaved” and will only
enter valid valid unsigned values. Be sure to state any additional simplifying assumptions that
you make.
3 Displaying the Mean
In this final Stage of the assignment, you will extend your program to display the mean computed
in Stage 2. The result must be displayed in decimal form.
You can use the BL sendchar instruction to display an ASCII symbol on the console. This
instruction displays the symbol corresponding to the ASCII code contained in R0.
Use the DisplayResult µVision project to develop your solution.
Suggested Approach
You can use the Divide program developed in a recent lab exercise to convert a value stored in
a register to the ASCII characters representing the value. One approach is to divide the mean
by decreasing powers of 10, using the whole part of the result as the next ASCII digit and the
remainder as the next value to be divided by the next lower power of 10.
For example, given the initial value 4128,
• Dividing 4128 by 1000 will give you a quotient of 4 and a remainder of 128. Therefore
0x04 + 0x30 = 0x34 (character ‘4’) will be the first ASCII character to be displayed.
• Dividing 128 by 100 will give you a quotient of 1 and a remainder of 28. Therefore
0x01 + 0x30 = 0x31 (character ‘1’) will be the second ASCII character to be displayed.
• etc.
You will need to choose an appropriate power of 10 to begin with. You can use the Power
program from the lecture slides to compute powers of 10.
You are required to document your approach to the development of the Simple Statistics Calculator program. Your documentation should be in the form of a typed document in PDF format.
This document must be submitted with your three assembly language .s source files. Documents
in a format other than PDF will not be graded.
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School of Computer Science and Statistics
CS1021 / Introduction to Computing I
Your report must contain the following:
A description of your solution to each of the three stages in the assignment. Your description
should make use of examples, diagrams and pseudo-code where appropriate. Your description must not take the form of a “narrative” for your assembly language program
(“I moved the value from R5 into R4. Then I added R4 to R3 and stored the result
in R0”). Such narratives will receive very low marks. Instead, try to describe how your
program works at a higher, conceptual level.
A detailed description of your methodology for testing each of the three stages from above.
This must include an account of the inputs used to test your program. Your report should
demonstrate that you have thoroughly tested each part of your program. You should give
careful consideration to choosing inputs that test different parts of your program (e.g. both
positive and zero inputs, zero-length sequences).
Explain why you are using each test input, document the outputs produced by your program
(all of the statistical measures, not just the mean displayed on the console). State whether
the output is correct and, if not, state why you think it is incorrect. Presenting your tests
and results in the form of a table is highly recommended.
The following broad marking scheme will be used for the assignment:
• Stage 1 – Console Input – 20%
• Stage 2 – Sample Sequence and Statistic Computation – 25%
• Stage 3 – Displaying the Result (Mean) – 30%
• Documentation – 25%
Note that marks will be awarded for both the content and presentation of your document. Solutions that are merely working will not automatically attract 100% of the marks available. Marks
will also be awarded for the quality of the solution.
Extra Mile
For each of the three stages in this assignment, 20% of the marks available will be awarded for
going the “extra mile”. How you do this is up to you. The following are some examples of
features that may be worthy of these marks:
• Allowing the user to enter either positive or negative values.
• Computing additional statistical measures.
• Formatting the mean in some way (e.g. preventing leading zeros from being displayed),
displaying results other than the mean.
• Correctly displaying negative results.

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