Assignment 3, Solutions

        USE     "hawk.h"
.       =       0
        LIS     R1,1
        ADDI	R2,R1,1
        LIL     R3,3
        MOVE    R4,R2
        ADDSI   R4,2
        ADD     R5,R3,R2

a) If execution begins at location zero and all 6 of the above instructions are executed, what values do these instructions leave in registers? (0.5 points).

Here is the Hawk emulator display of the result of executing this code:

 HAWK EMULATOR
   /------------------CPU------------------\   /----MEMORY----\
   PC:  00000010                R8: 00000000   000004: BNS     #000006
   PSW: 00000000  R1: 00000001  R9: 00000000   000006: LIL     R3,#000003
   NZVC: 0 0 0 0  R2: 00000002  RA: 00000000   00000A: MOVE    R4,R2 
                  R3: 00000003  RB: 00000000   00000C: ADDSI   R4,#2
                  R4: 00000004  RC: 00000000   00000E: ADD     R5,R3,R2  
                  R5: 00000005  RD: 00000000 ->000010: NOP
                  R6: 00000000  RE: 00000000   000012: NOP
                  R7: 00000000  RF: 00000000   000014: NOP

b) Show the contents of the memory locations that hold the above code. That is, show what the assembler (plus the loader) put into RAM when the above code is assembled. (1.0 points)

Hitting the t key (toggle memory display) in the Hawk emulator shows the contents of memory in hexadecimal:

 HAWK EMULATOR
   /------------------CPU------------------\   /----MEMORY----\
   PC:  00000000                R8: 00000000 -*000000: 61F201D1 Q ra 
   PSW: 00000000  R1: 00000000  R9: 00000000   000004: 03E30001   c
   NZVC: 0 0 0 0  R2: 00000000  RA: 00000000   000008: F2F40000   tr
                  R3: 00000000  RB: 00000000   00000C: 3235C214  B52
                  R4: 00000000  RC: 00000000   000010: 00000000
                  R5: 00000000  RD: 00000000   000014: 00000000
                  R6: 00000000  RE: 00000000   000018: 00000000
                  R7: 00000000  RF: 00000000   00001C: 00000000

Note: Both of the above problems are typical exam questions from the first midterm. You must learn how to do this by hand, but you can check your answers using the assembler and the Hawk emulator.

An Exercise From The Text: Do exeercise l) from Chapter 4, at the end of the section on Memory Reference Instructions.

Translate a = (b - 64) + c to Hawk assembly code, assuming that the variables a, b and c are stored in memory at words 10000₁₆ through 10008₁₆ in that order.

A       =       #10000  ; memory addresses for variables
B       =       #10004  ; (could just use literals)
C       =       #10008

        LIL     R3,B
        LOADS   R3,R3   ; R3 = b
        ADDI    R3,-64  ; R3 = b - 64
        LIL     R4,C
        LOADS   R4,R4   ;    R4 = c
        ADD     R3,R3,R4; R3 = (b - 64) + c
        LIL     R4,A
        STORES  R3,R4   ; a  = (b - 64) + c

Background: Suppose you wanted to come up with a general rule for load immediate. You could express this as a macro called LI that would automatically select the best load instruction. The following macro does this in SMAL, given appropriate values for x, y, z and w.

        MACRO LI =dst, =const
          IF (const > x) & (const < y)
            LIS dst,const
          ELSEIF (const > z) & (const < w)
            LIL dst,const
          ELSE
            LIW dst,const
          ENDIF
        ENDMAC

A Question: Give the appropriate values for x, y, z and w. (0.5 points)

x   =   -129
y   =    128
z   = -32769
w   =  32768

A Problem: When you run the Hello World program from Chapter 5, what are the values of the registers immediately prior to the execution of the JSRS instruction that calls puts()? (0.5 points)

This problem was designed to force students to run the hawk emulator.

 HAWK EMULATOR
   /------------------CPU------------------\   /----MEMORY----\
   PC:  0000100E                R8: 00000000  *001000: STORES  R1,R2
   PSW: 00000100  R1: 000001FA  R9: 00000000   001002: LEACC   R2,R2,#0004
   NZVC: 0 0 0 0  R2: 00010040  RA: 00000000   001006: LIL     R3,#001018
                  R3: 00001018  RB: 00000000   00100A: LIL     R1,#0001FA 
                  R4: 00000009  RC: 00000000 ->00100E: JSRS    R1,R1
                  R5: 00000000  RD: 00000000   001010: LEACC   R2,R2,#FFFC
                  R6: 00000000  RE: 00000000   001014: LOADS   R1,R2   
                  R7: 00000000  RF: 00000000   001016: JSRS    R0,R1