Due date: See Class Webpage

0. Preparations

• To do this project, you must obtain a copy of the prepared files with these commands:

  mkdir ~/cs255/pj7 cp /home/cs255001/Handouts/pj7/* ~/cs255/pj7

1. Project Description

Write a Bubble sort subroutine in ARM assembler language. Some of you may have forgotten what the Bubble sort algorithm is, so let me describe that in Section 2.

2. The BubbleSort Algorithm

For those who does not know what bubble sort is, the following is the C++/Java program that you need to implement:

// How the variables are used: // // input A: array of integers that needs to be sorted // N: size of array A // // Done: integer (functioning as a boolean: 0 = false, 1 = true) // Help: integer (help variable for swapping) void BubbleSort(int[] A, int N) { Done = 0; // 0 represents false k = 1; while (Done == 0) { Done = 1; // 1 represents true. for (i = 0; i < N-k; i++) { if (A[i] > A[i+1]) { Help = A[i]; A[i] = A[i+1]; A[i+1] = Help; Done = 0; // Not sorted... } } k = k + 1; } }

Basically, the bubble sort algorithm swaps two adjacent elements A[i] and A[i+1] when the latter is smaller. When two adjacent element are exchanged, the Done variable is set to FALSE , indicating that another iteration is necessary.

3. The main Program

I have provided a main program that calls your bubble sort subroutine.

The main program is stored in the file pj7.s

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The main program will call (i.e., executes a bsr BubbleSort instruction) the BubbleSort subroutine twice, each time with a different array.

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The main program calls the BubbleSort with 2 parameters:

The address of the array that needs to be sorted The number of elements in the array

The type of the elements of the array is int.

The main program passes the parameters as follows:

the address of the array is stored in register r0 and the number of elements of the array stored in register r1.

Here are the code segments that shows you how the main program calls the BubbleSort subroutine:

movw r0, #:lower16:A // Pass address of the array A in r0 movt r0, #:upper16:A mov r1, #5 // Pass size of the array in r1 bl BubbleSort // Call BubbleSort to sort array A (5 elements) .... movw r0, #:lower16:B // Pass address of the array B in r0 movt r0, #:upper16:B mov r1, #10 // Pass size of the array in r1 bl BubbleSort // Sort array B (10 elements)

Therefore, your BubbleSort subroutine must use as parameters:

r0 = address of the array to be sorted r1 = number of elements in the array

Note:

When the BubbleSort subroutine returns, the array that was passed to BubbleSort will become sorted

4. The bubblesort.s program file

• Write your BubbleSort subroutine inside the file bubblesort.s.

  Right now, the bubblesort.s looks like this:

  .global BubbleSort BubbleSort: //***************************************************** // Write your bubble sort assembler subroutine here // // BubbleSort: input r0 = address of int array // r1 = # elements in the array //***************************************************** // Write your bubble sort function here..... // Make sure you RETURN to the caller !!! .data // ************************************************************************* // If you need local variables, you can define them below this line // ************************************************************************* .end

  You must write the BubbleSort function in ARM assembler code and put the code after the BubbleSort (and before the .data directive)

  Make sure you use the parameter passing agreement defined above !!!

  This is also the file that you must turn in.

5. Compile and run project 7

• You can compile pj7 with EGTAPI's file browser as follows:

  1. First: press the CONTROL key and select pj7.s 2. THEN: press the CONTROL key and select bubblesort.s NOTE: the ORDER of clicking is VERY IMPORTANT DO NOT click on bubblesort.s first !!!! (A wrong order will cause EGTAPI to generate the output "bubblesort.arm" and not "pj7.arm") 3. Finally: click "Compile" NOTE: You MUST see the digit "1" next to the "pj7.s" file before you click "compile" or else, EGTAPI will generate a WRONG assembler output filename !!!

  If you have a hard time using the CONTROL + click to compile the project, you can also compile the programs in this project, by opening the Terminal in EGTAPI and type the follow commands:

  cd ~/cs255/pj7 // Execute this once /home/cs255001/bin/as255 pj7.s bubblesort.s

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• To run this project:

  If compilation is successful, you will see pj7.arm in the file list in EGTAPI Click on pj7.arm and click Select to run it.

6. The Egtapi Debug file

I have prepared a egt.pj7.arm file that displays the arrays used in this project. You have copied this file in the preparation step.

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I am sure you will have bugs in your program with this assignment.

So check (read !!!) out Section 4 + 5 of Project 6 ( click here ) and the Section 9 and 10 in the Egtapi manual ( click here ) on how to: set break points and use breakpoints to debug your assembler program.

The breakpoints are very helpful in finding errors in assembler programs.

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• Correct behaviour:

  When the program starts, you should see 2 unsorted array (named A and B) in the Array window (you must click on the "Array" tab to see them). When you click on Run (double arrow), the program will stop at the label BubbleSort I made the program stop at the start (beginning) of the BubbleSort function to help you debug the program When you click on Run again, the program will stop at the label sortB The array A (in the "Array" windown) will now be sorted When you click on "Run" (double arrow) again, the program will stop at the label BubbleSort again (because it is a breakpoint) Click "Run" again, and the program will stop at the label Stop: The array B (in the "Array" window) will now be sorted

7. Turn in

Turn in your source file bubblesort.s as pj7 using the /home/cs255001/turnin command (executed while you're in your cs255 directory).

Open the Terminal in EGTAPI and type in these commands:

cd ~/cs255/pj7 /home/cs255001/turnin bubblesort.s pj7 // If you're in section 1 or /home/cs255002/turnin bubblesort.s pj7 // If you're in section 2

You do not need to turn in the pj7.s file !!!

As usual, I want the source (so I can read it). DO NOT turn in the executable or the object code !

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• Extension request
  • To request an extension for pj7, you must execute the following command (using EGTAPI's "Terminal") before the deadline of the homework:

    /home/cs255001/req-ext pj7 // If you're in section 1 or /home/cs255002/req-ext pj7 // If you're in section 2

    You request will be successful if you have not exceeded the maximum number of "free" (no-questions-asked) requests allowed