ECE5484-Project 2 Solved

The objective of this project is to reinforce your understanding of computer organization, instruction set architectures, and assembly language. You will accomplish this by writing, analyzing, and debugging an assembly language program for the MARIE processor.

You must:

i)       design and write an assembly language program for the MARIE processor that inputs, transforms,

stores, and then outputs a sequence of characters from the set A-Z;

ii)      debug and test your program by simulating it using the MARIE simulator;

iii)    document your work in a short report; and

1.     The MARIE Simulator
The MARIE simulator is provided as a zip file containing Java archives (*.jar) files, documentation, and example source files. Unzip the file to a directory for use. Do the following to become familiar with the MARIE simulator.

•     Read “A Quick Start Guide for the MARIE Machine Simulator Environment” (QuickGuide.pdf provided in the zip file).

•     Depending on how comfortable you are with using the MARIE simulator after reading the quick start guide, you may also wish to read “A Guide to the MARIE Machine Simulator Environment” (MarieGuide.pdf provided in the zip file).

•     Review the example assembly language source files and experiment with the MARIE simulator using these examples. The Ex4_3.mas and Ex4_4.mas examples are likely the most relevant to this assignment.

2.     Design Specification
You are to design, write, test, and debug a MARIE assembly language program that inputs a sequence of characters from the set A-Z (capital letters only), stores each character in memory after it is transformed by the trivial ROT13 cipher, and then, after character input completes, outputs the transformed characters.

A template source code file (Project-2_Start.mas) is provided with this assignment. Edit this file to create a program that meets the program specifications. Note that the template includes instructions to initialize some working values that your program can use. The template also defines memory locations. You may add data memory locations. The program can be designed without additional data locations, but it may be necessary to do so for your design.

For full credit, your solution must perform the functions and satisfy the requirements specified below.

a)    The first instruction of the program must be placed at location (address) 0x100 (100 hexadecimal) in MARIE’s memory. This is accomplished by following the program template that is provided.

b)    The constant data values (One, ChA, ChZ, ChPe, Val13, Start) should not be changed by the program. The program can load from these memory locations, but should not store to them.

c)    Transformed input characters must be stored in successive memory locations beginning at location 0x200 (200 hexadecimal) as indicated in the program template. The program should store all transformed input characters before any characters are output.

d)    The program should always initialize the values for Ptr in the working data memory and not rely on the values for these locations that are defined in the assembly source file. This initialization is done by the provided template file.

e)    The program should work for any inputs ‘A’ through ‘Z’ and ‘.’ (a period terminates input). In the interest of keeping the program simple, the program does not need to validate inputs.

f)     When transformed characters are stored and when transformed characters are output, the program must use a loop and indirect addressing to access the values in the array of words. Note that variable Ptr is initialized in the template code and should be used in the loop. You may also define a Count variable to count the number of characters, but there are also correct designs that do not require a Count variable.

The program should operate as follows.

Input Phase:

1.   A character (A-Z or ‘.’) is input. MarieSim allows the user to input a single character that is read into the accumulator (AC) with an Input instruction.

2.   If character ‘.’ (period) is input, then the input phase ends and the output phase begins (step 5 below). (The period may be stored in memory to mark the end of the characters or the characters can be counted to determine how many transformed characters to output during the output phase.)

3.   The character that is input is transformed using the trivial ROT13 cipher (see Section 5.1).

4.   The transformed character is stored in the next location in the block of memory beginning at location

Start. (Variable Ptr must be updated and indirect memory addressing must be used.)

Output Phase:

1.   All transformed characters are output, beginning with the first character that was transformed. The ‘.’ character is not to be output. (This will require a loop using variable Ptr and indirect addressing. Note that the number of characters to output will vary and the program must know when to stop the output by relying on a ‘.’ or other special character in memory, counting the number of input characters during the input phase, or some other method.)

2.   After all characters are output, the program halts by executing the HALT instruction.

Make sure you project has both distinct phases. You could, but don’t have to, use the idea of “subroutines” or “functions” to handle each distinct phase.

3.     Testing
Test and debug the program using the MARIE simulator (MarieSim.j Debug the program using the “Step” and “Breakpoint” features of simulator. You must test your program with the following two test cases.

Test 1: Input the eight-character sequence “VIRGINIA” followed ‘.’ to terminate the input. Note that you need to input one character a time into MarieSim’s ASCII Input area, with each character followed pressing the “Enter” key. The ROT13 value of each character (“IVETVAVN” should be displayed after the ‘.’ character is input.

Test 2: Rerun the program in MarieSim, without reassembling or reloading, then input the four-character sequence “GRPU” followed ‘.’ to terminate the input. Note the output.

When you create your source file within MarieSim (using the File menu pick), use file name lastname_firstname_P2.mas, where “lastname” is your last or family name and “firstname” is your first given name. You can assemble your source file in the editor program. The assembly process creates a listing

(lastname_firstname_P2.lst) and an executable (lastname_firstname_P2.mex). Load the executables file

into simulator for execution.

4.     Design Notes
4.1.      The ROT13 Cipher
The ROT13 cipher (see http://en.wikipedia.org/wiki/ROT13) is an but trivial cipher that simply rotates the characters by 13 positions. For example, ‘A’ is transformed to ‘N’, ‘Z’ is transformed to ‘M’, and so on.

The Project-2_Start.mas source file includes a ROT13 subroutine almost performs this transformation. You need to fix one bug in subroutine.

4.2.      Tips for Program Design and Debugging
Here are some suggestions to keep in mind as you design and implement your program.

•     Design and test your program in an iterative manner, building from simple functionality to full functionality. For example, first write a program that inputs characters and just stores them in memory. Then, add the code to transform the characters using ROT13 before they are stored (and fix ROT13). Then complete the program by adding code to output the transformed characters.

•     Study sample code in the textbook. For example, Example 4.4 (page 260) provides code that traverses and outputs a string. (Sound familiar?) Example 4.5 (page 260-261) shows code that calls a subroutine. The operand used with the Skipcond instruction is a source of frequent errors, so study the examples, such as Example 4.4 (page 260), to be sure you understand how to specify the operand for Skipcond.

•     Correct solutions for the project require that about 25 to 30 instructions are added to the template. If you find that you are using significantly more instructions than this, you should reconsider your design and, as needed, consult with the GTA and/or instructor.

•     When debugging your program, set a breakpoint in MarieSim to execute past the input operation and then single-step through the program to ensure the code is doing what you want it to do.

•     When debugging and testing, be sure that “ASCII” is selected for the input and output windows in MarieSim.

•     An “Instruction Set Cheat Sheet” can be displayed from the “Help” menu in the MARIE Assembler Code Editor.