Having trouble finding error in my assembly code

Question

I am a beginner when it comes to assembly language. I am using "easy 68k editor/assembler" to write 68k assembly code that asks the user for 2 values, then sum them up together and display it. The problem is that my code keeps getting halted and I am not sure how to troubleshoot/debug this problem.

Can anyone help me figure out how to track down the error? I will be grateful. Thank you in advance.

*-----------------------------------------------------------
* Program    : Sum of Two Numbers
* Written by : Me
* Date       : July 15, 2012
* Description: This program will read in 2 numbers the user
*inputs and find the sum.
*-----------------------------------------------------------

    org     $8000

    START       movea.l #MSG1, A3
                trap    #3
                clr.w   D2
                JSR     Loop
                trap    #2
                move.w  d2, d4
                movea.l #msg2, a3
                trap    #3
                clr.w   d2
                jsr     loop
                trap    #2
                movea.l #msg3, A3
                trap    #3
                add.w   d4, d2
                JSR     DISP
                trap    #2
                trap    #9
    LOOP        trap    #0
                trap    #1
                cmp.b   #$0D, D1
                BEQ     BREAK
                and.b   #$0F, d1
                mulu    #10, d2
                add.w   d1, d2
                jmp     loop
    Break       rts
    DISP        clr.b   d3
    DISDIV      divu    #10, D2
                move.b  #16, d5
                ror.l   d5, d2
                or.b    #$30, d2
                move.b  d2, -(A7)
                addq    #1, d3
                clr.w   d2
                ror.l   d5, d2
                bne     DISDIV
    DISDIG      move.b  (a7)+, D1
                trap    #1
                subq.b  #1, D3
                bne     DISDIG
                rts
                org     $8100
    MSG1        DC.B    'Please enter the first of two numbers (two digits) ', 0
    MSG2        DC.B    'Please enter the second of two numbers (two digits) ', 0
    MSG3        DC.B    'The sum of the two 2 digit numbers you entered is ', 0
                end     start

If there is another forum i can be better off posting this in, please let me know. Thank You — The Tokenizer, Jul 15 '12 at 17:39
Can't step through it in a 68000 simulator and see where it fails? — Martin Wickman, Jul 15 '12 at 17:41
I know where it fails. i just dont know why. Its a trap exception where i call my first trap #3. — The Tokenizer, Jul 15 '12 at 18:14
If you know where it fails, why not say so in the question? The more information you provide the more likely somebody will be able to help. — Raymond Chen, Jul 15 '12 at 19:00
What is `trap #3` supposed to do? What are its parameters? Better yet, post a link to the API the code is using so we can figure it out. — wallyk, Jul 15 '12 at 19:02

score 1 · Answer 1 · answered Jul 16 '12 at 16:32

1

Your code should start with:

LEA    MSG1, A1
MOVE.B #14, D0
TRAP   #15

This will display the first message to the user. Check out the EASy68K home page for more information on invoking I/O traps.

answered Jul 16 '12 at 16:32

TMN

3,060
21
23

score 0 · Accepted Answer · answered Jul 16 '12 at 14:18

Most likely the traps you are using are not those used by Easy68K. Look here for the traps used by Easy68K.

The function of the trap instructions is not defined by the 68K assembly language, but rather assigned by the operation system (if the OS makes use of the traps at all, some just ignore them). If you execute a trap instruction the 68000 just executes the code the trap vector points to. There is no "buildin" function assigned to any trap.

Having trouble finding error in my assembly code

2 Answers2