CS/ECE 252 Introduction to Computer Engineering

1. Run the program on PennSim and give a brief explanation of what it does.
2. How many times does the LOOP execute?
3. What value will be contained in R3 after the execution of the program?

Problem 2 (4 points)

The following LC-3 program compares two characters strings of the same length; the source strings are in the .STRINGZ form. The first string starts at memory location x4000, and the second string starts at memory location x4100. If the strings are the same, the program terminates with a value 1 in R5, otherwise R5 is 0. Insert instructions at (a), (b) and (c) that will complete the program

 
	
            .ORIG x3000
            LD R1, FIRST
            LD R2, SECOND
            AND R0, R0, #0
LOOP        ----------------(a) 
            LDR R4, R2, #0
            BRz NEXT
            ADD R1, R1, #1
            ADD R2, R2, #1
            ----------------(b) 
            ----------------(c) 
            ADD R3, R3, R4
            BRz LOOP
            AND R5,R5, #0
            BRnzp DONE
NEXT 	    AND R5, R5, #0
            ADD R5, R5, #1
DONE 	    TRAP x25
FIRST 	    .FILL x4000
SECOND 	    .FILL X4100
            .END

Problem 3 (5 points)

Consider the following LC-3 assembly language program:

 

        .ORIG x3000
        LD R0,INPUT
        AND  R1, R1, #0 
        ADD  R4, R1, #1
        ADD  R3, R0, #0 
	  

L00P    ADD R1, R1, R0
        ADD R3, R3, #-1
        BRp  L00P
	
        ADD R3, R3, R0
        ADD R0, R1, #0
        ADD R3, R3, #-1
        ADD R4, R4, #-1
        BRz  L00P
        BR DONE
INPUT   .FILL x0003
RESULT  .FILL x0000
DONE    ST R0,RESULT
        HALT

1. Show the symbol table created by the assembler for the above program.
2. Once the symbol table is created, the assembler then creates a binary version (.obj) of the program. Show the LC-3 machine code for the above program.

Problem 4 (9 points)

In this problem you are to write an assembly program that converts lower case alphabet characters to upper case alphabet characters. The input to the program is from the keyboard and the output is sent to the (display) screen. Make use of the template code provided in q4.zip along with the test scripts.

You have to implement the following functionalities in the program:

1. Code to check for the termination character. If the user enters the termination character (“!”), the program will display the message “Finished successfully!” on the screen and will terminate.
2. Code to check whether the input is a valid character. Only uppercase and lower case alphabets are considered valid characters; other characters (other than the termination character) are considered invalid. On getting an invalid input, the program should display an error message and then ask for a new input.
3. Code to check whether an input is a lower case or upper case character. If the entered input is a lower case character, convert it to the corresponding upper case character.
4. Code to display the uppercase alphabet characters on the screen.
5. Keep doing the above until the user enters the termination character “!”

Your program should use subroutines for all the major functions.

To run the test for q4, type the following line into the Pennsim command line:

 
script test1.sc 

Your test is considered a failure if you see some messages having the FALSE keyword on the output command window when you run the test script. If your program is called something other than q4.asm you should either change its name or edit the script file, but make sure to rename it to q4.asm when you submit it to the Learn@UW DropBox.

The grading scheme for this problem will be as follows:

1. Code assembles and has comments (1 point)
2. Terminates on “!” (1 point)
3. CheckInput; checks whether the input is valid (3 points)
4. IsUppercase; checks whether the input is already in uppercase (2 points)
5. ConvertToUppercase (1 point)
6. DisplayChar; display the upper case alphabet (1 points)

Problem 5 (9 points)

For problem 5, you have to further modify the GetInput and DisplayChar functionality of problem 4. Now, instead of getting input from the user, you will read a section of the memory from x7000 to x7013 (both inclusive). Instead of displaying the output at the console you will have to only write the uppercase alphabets to memory location starting from x7100. Thus in this part there is no need to check the termination character. In addition, you will need to implement some counters:

1. Count the total number of invalid (i.e., non-alphabet) characters and write the result into memory location x70FF
2. Count the total number of characters which are already in upper case and write the result into memory location x70FE
3. Count the total number of character which have been converted to upper case by your program and write the result into memory location x70FD

 
script test2.sc 

Your test is considered a failure if you see some messages having the FALSE keyword on the output command window when you run the test script. If your program is called something other than q5.asm you should either change its name or edit the script file, but make sure to rename it to q5.asm when you submit it to the Learn@UW DropBox.

The grading scheme for this problem will be as follows:

1. Code assembles and has comments (1 point)
2. Modifying the input mechanism to read from memory (2 points)
3. Modifying the display/output sub routine to write data to memory (2 points)
4. Count the total number of invalid characters (1 point)
5. Count the total number of characters which are already in upper case (2 points)
6. Count the total number of character which has been converted to upper case (1 point)