Assignment 3 Solution

For this assignment, only an electronic submission (attachments) at owl.uwo.ca is required.




Attachments must include:




o ONE pdf file that has one flowchart, program documentations, and any related communications.

o Text soft copy of the assembly source programs that you wrote for each question (one program attachment per question), i.e., THREE assembly source files in total.




So, in total, you will submit 1 + 3 = 4 files.




Failure to follow the above format may cost you 10% of the total assignment mark.




Late assignments are strongly discouraged




10% will be deducted from a late assignment (up to 24 hours after the due date/time) After 24 hours from the due date/time, late assignments will receive a zero grade.




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 SSC-1032 and HSB-14 labs.




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 is very important in assembly language. It is expected to do the following in your programs:




Using macros for the constants in your program 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 using any whitespace at all




Not bothering to comment




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)




Handing it in as soon as it assembles without testing and/or trying to break your code































Mahmoud El-Sakka.

Strings




A string is an array representing a sequence of characters. To store a string of n characters in your program, you need to set aside n+1 bytes of memory. This area of memory will contain the characters in the string, plus one extra special character—the null character—to mark the end of the string. The null character is a byte whose bits are all zeros (0x00). The actual string consists of any group of characters, which none of them can be the null character.




QUESTION 1 (20 marks)




Write an ARM assembly language program to concatenate two stings (STRING1 and STRING2) and store the result in a null terminated STRING3. Assume that the length of STRING1 + the length of STRING2 ≤ 255.

Your code should be highly optimized, i.e., use as little number of instructions as possible.

You may want to define the strings as follow:
;String1
STRING1
DCB "This is a test string1"
EoS1
DCB 0x00
;end of string1
STRING2
DCB "This is a test string2"
;String
EoS2
DCB 0x00
;end of string2
STRING3
space 0xFF





QUESTION 2 (40 marks)




Draw a detailed flowchart and write an ARM assembly language program to copy a null terminated STRING1 to a null terminated STRING2, after removing any occurrences of the word “the” in STRING1. I.e., if STRING1 is




“the woman and The man said the” then STRING2 would become “ woman and The man said ”. However, if STRING1 is “and they took breathe” then STRING2 would become “and they took breathe” without any change.




Your code should be highly optimized, i.e., use as little number of instructions as possible.

You may want to define the strings as follow:
;String1
STRING1
DCB
"and the man said they must go"
EoS
DCB
0x00
;end of string1
STRING2
space 0xFF


More test cases:


the"  "
123
"


"the the


the 123


""""














"the"  ""












"The"  "The"


the1"




"them
the
the1"  "them







QUESTION 3 (40 marks)




Write an ARM assembly language function (subroutine) that takes a data value stored in register r0 and returns a value in r0 as well. The function returns y = a × x2 + b × x + c where a, b, and c are signed integer parameters built into the function (i.e., they are not passed to it) and are defined in the memory using three DCD instructions. The subroutine also performs clipping, i.e., if the output is greater than a value d, it is clipped to d, where d is another parameter defined in the memory using a DCD instruction. The input in r0 is a signed integer binary value. Apart from r0, no other registers may be modified by this subroutine, i.e., if you want to use any register as a working register, you have to store its value in a safe place first prior changing it, and to restore this value before returning from the function.




After implementing the function, write an assembly program which stores a value in r0 and calls your function. Once the control is returned back from the function, the program will double the returned value and store this doubled value in r1.




Your code should be highly optimized, i.e., use as little number of instructions as possible.




Example1: if a = 5, b = 6, c = 7, d = 90, and r0 = 3,

then the returned value in r0 should be 70 and the value in r1 will be 140.

Example2: if a = 5, b = 6, c = 7, d = 50, and r0 = 3,




then the returned value in r0 should be 50 and the value in r1 will be 100.

Example3: if a = -5, b = 6, c = 7, d = 10, and r0 = 3,

then the returned value in r0 should be -20 and the value in r1 will be -40.










Mahmoud El-Sakka.