CS2208b Assignment 3

CS2208b Assignment 3

For this assignment, only an electronic submission (attachments) at owl.uwo.ca is required.
 Attachments must include:
o ONE pdf file (named report1.pdf) that has a flowchart for question 2.
o TWO Text files (named question1.s and question2.s) that have softcopy of the assembly source
programs you wrote for each question (one program per file), i.e., TWO assembly source files in total.
 So, in total, you will submit 1 + 2 = 3 files (report1.pdf, question1.s and question2.s)
 Failure to follow the above format may cost you 10% of the total assignment mark.

In this assignment, you will use the micro Vision ARM simulator by Keil, which is an MS Windows-based
software, to develop the required programs in this assignment. The simulator (version 4) has been installed on all
PCs at GEN labs, except NCB-105.
The Keil micro Vision simulator may also be installed on your Windows PC. You just need to download it from
OWL and install it.
Programming Style
The programming style is very important in assembly language.
It is expected to do the following in your programs:
 Using EQU directive to give a symbolic name to a numeric constant to make it more readable.
 Applying neat spacing and code organization:
o Assembly language source code should be arranged in three columns: label, instruction, and comments:
 the label field starts at the beginning of the line,
 the instruction field (opcodes + operands) starts at the next TAB stop, and
 the comments are aligned in a column on the right.
 Using appropriate label names.
 Commenting each assembly line
 Commenting each logical part of your code.
Great Ways to Lose Marks
 Not grouping your lines into logical ideas
 Not appropriately using whitespace
 Not bothering to comment your code
 Commenting the code by just stating what you're doing, instead of why, e.g.,
MOV r0, #5 ;move 5 into r0
 Not paying attention to the programming style (see the previous paragraph)
 Not optimizing your code by using unnecessary assembly instructions. The more instructions in your program
the less your mark will be.
 Handing in your code as soon as it assembles, without testing and validating your code
 Not using proper flowchart symbols
 Not following the flowchart rules
Copyright © 2020 Mahmoud El-Sakka.
QUESTION 1 (45 marks)
Most goods sold in Canadian and U.S. stores are marked with a Universal Product Code (UPC).
The meanings of the digits underneath the bar code (from left to right) are:
 First digit: type of item,
 The first group of five digits: manufacturer,
 The second group of five digits: product, and
 Final digit: check digit, used to help identify an error in the preceding digits.
To verify that the check digit is valid (i.e., there is no error in the code) or not,
 Add the first, third, fifth, seventh, ninth, and eleventh digits
 Add the second, fourth, sixth, eighth, tenth, and twelveth digits
 Multiply the first sum by 3 and add it to the second sum
 If the sum is multiple of 10, the 12 digit UPS is valid.
Example for UPC 0 13800 15073 8:
 First sum: 0 + 3 + 0 + 1 + 0 + 3 = 7
 Second sum: 1 + 8 + 0 + 5 + 7 + 8 = 29
 Multiplying the first sum by 3 and adding the second yields 50
 50 is multiple of 10, the 12 digit UPS is valid
Write an ARM assembly program to verify whether a string of 12 ASCII encoded digits stored in memory is a valid
UPC or not. If valid, you should store 1 in r0, if not, you should store 2 in r0. Your code should be highly optimized.
Use as few instructions as possible (as little as 19 assembly instructions only, NOT including any assembly directives
or data definitions)!!.
Define in your assembly program the 12 digits UPC string as follow:
UPC DCB "013800150738" ;UPC string
To test your program, you can use the following UPCs:
0 60383 75557 7
0 65633 45471 2
You can also get more UPCs from your kitchen items.
HINT 1: To load a byte to a register, use LDRB, not LDR.
HINT 2: To calculate 3 × Z, you can do so using only one ADD instruction with LSL#1 shift.
HINT 3: You can implement the division operation using repeated subtraction.
QUESTION 2 (55 marks)
Draw a detailed flowchart and write an ARM assembly program to determine whether a string of printable ASCII letters
(from a to z or from A to Z, case insensitive) stored in memory is a palindrome (i.e., the letters in the string are the same from
left to right as from right to left, case insensitive) or not. If palindrome, you should store 1 in r0, if not, you store 2 in r0.
Your code should be highly optimized. Use as few instructions as possible (as little as 21 assembly instructions only
NOT including any assembly directives or data definitions)!!.
Ignore all characters that are not letters. You should also treat capital and small letters the same, i.e., case insensitive. For
example, “madam”, “deleveled”, “Noon”, “He lived as a devil, eh?”, and “Was it a car or a cat I saw?” are palindrome
strings. However, “madam, I am Adam.” is not a palindrome string.
A string can have an even or odd number of characters and must end with character 0x00 (i.e., the ASCII code of the null
character).
Define in your assembly program the string as follow:
STRING DCB "He lived as a devil, eh?" ;string
EoS DCB 0x00 ;end of string