CS/ECE 252 Introduction to Computer Engineering Spring 2007 Sections 1 and 2 Instructor Mark D. Hill and TAs Marc de Kruijf & Sanghamitra Roy URL: http://www.cs.wisc.edu/~markhill/cs252/Spring2007/

Homework 7 // Due at Lecture Wed April 25

You may do this homework in a group of two students from the same 252 section and turn in one solution at lecture with BOTH students names at the top.

First contact for questions is TA Sanghamitra Roy at: roy1@wisc.edu

The following homework requires you to use the LC-3 simulator. Please follow instructions from HW #5 problem 8 for opening the LC-3 simulator and instructions from HW #6 for submitting screenshots of your code.

1.      An assembly language program is given below:

.ORIG              X3000

                                    LD                   R2, ZERO

                                    LD                   R0, M0

                                    LD                   R1, M1

            LOOP              BRz                  DONE

                                    ADD                R2, R2, R0

                                    ADD                R1, R1, -1

                                    BR                   LOOP

DONE             ST                    R2, RESULT

                                    HALT 

RESULT          .FILL               X0000

ZERO              .FILL               X0000

M0                   .FILL               X0500

M1                   .FILL               X0005

                           .END

a.       Run the given program in the LC-3 simulator and describe what the program does.  

b.      How many times does the program loop?

c.       What is the value contained in RESULT after the program runs to completion?

(No screenshots required for this problem.)            

2.      Problem 7.13 on page 193 of ItCS.

3.      Write an LC-3 assembly language program that finds out whether the value stored in R0 is divisible by the decimal number 3. If divisible, the program stores a 1 in R1, otherwise it stores a 0 in R1. Your solution should use a looping construct. A simple algorithm for this problem would be to subtract 3 repeatedly from R0 and check whether the result is zero.

a.       Use x12FF as the value in R0 and submit a screenshot of your executed code in the LC-3 simulator showing the value in R1.

b.      Also submit a printout of your commented code in assembly language (.asm file)

4.      Create a symbol table for the following LC-3 program:

                              .ORIG              X3000

                              LD                   R0, NUMBERS

                              LD                   R2, MASK

LOOP              LDR                 R1, R0, #0

                              BRz                  DONE

                              AND                R5, R1, R2

                              BRz                  L1

                              BRnzp              NEXT

L1                    ADD                R1, R1, R1

                              STR                 R1, R0, #0

NEXT              ADD                R0, R0, #1

                              BRnzp              LOOP

DONE             HALT

NUMBERS     .FILL               x4000

MASK             .FILL               x8000

.END