Computer Systems Organization (Tietokoneen toiminta ) Autumn -99

Exercise 3 (8.-12.11.)


Please note that there are a couple of guides to the TTK-91 assembly language available also in English at the following addresses: http://www.cs.Helsinki.FI/~marttine/titokoksieng1.html and http://www.cs.Helsinki.FI/~marttine/titokoksieng2.html. Some further information about assembly languages can be found in Tanenbaum (4th edit.) pp. 322 - 354, Tanenbaum (2rd edit.) pp. 350 - 354 and in van de Goor chapters 4 - 7.

1. Simulate the execution of the following program. What is the output, if you enter the month of your birth as input? And what would happen, should you enter a negative number? 

  Alku  LOAD  R1,=0
        STORE R1,15
        IN    R2,=KBD
        STORE R2,14
        LOAD  R3,15
        ADD   R3,14
        STORE R3,15
        LOAD  R4,14
        SUB   R4,=1
        STORE R4,14
        JPOS  R4,4
        LOAD  R5,15
        OUT   R5,=CRT
  Loppu SVC   SP,=HALT
b) The program makes use of direct memory addresses. However, symbolic variable names could be used instead while letting the compiler to do the mapping between names and addresses. Try to make the code more 'readable' and easier to manipulate.
c) Optimize the code, i.e. delete the commands you find unnecessary.

2. a)What do the following commands do? Let jatko be 100 by value and let a be 120. Register R2 has the value 20. 

        IN    R1,=KBD
        MUL   R1,=7
        STORE R1,a
        JUMP  @jatko(R2)

b) The contents of some registers and memory words are as follows: 

  R1: 0, R2: 10, R3: 100 

  MP 100: 200, MP 110: 300, MP 200: 400, 
  MP 300: 500, MP 400: 400
What are the contents of R1 after the following instructions? Instructions are done in the given order. 
  1) LOAD R1, 100(R2)  2) LOAD R1, =100(R3)  3) LOAD R1, @R3      
  4) LOAD R1, R3       5) LOAD R1, @100(R2)  6) LOAD R1, @400(R1)
(Tanenbaum: Addressing, pp. 213 - 218.)

3. There are one hundred students taking a course. The exam results (points) are stored to the subsequent memory words 100, ..., 199. Write an assembly language program to display the average exam result.

4. Make an assembly language program which displays the factorial of a positive integer entered by the user. (The factorial of a positive integer is the product of the number itself and the integers which are smaller than the said number and greater than zero. For example, the factorial of five is 5*4*3*2*1, i.e. 120.)

5. Four bit strings were found from the main memory of the Koksi simulator. Below they are represented as hexadecimal numbers. 

    01 A0 00 A0
    18 47 00 01
    13 31 FF FF
    02 80 FF FE
Give the instructions in TTK-91 assembly language (hint: make a conversion into bit strings at first). What do the instructions do?

6.
a) Experiment with the KOKSI simulator. The simulator can be downloaded from the course home page. If you don't install it into your own computer, you may try it out in the the machines of the department. The simulator can be found at least in the machines of terminal room D427 (disk G under the Windows File Manager). Try to run your assembly language programs.
b) If you were to make a simulator like Koksi, how would you begin? Please do not go into details: the very general idea and the most important data structures are enough for this exercise.