Bdtjtk

I want to implement cursor movement using keys in my OS. I tried this code to do that:

mouse:

mov ah,0h

int 16h



    cmp al, 107

    je Down





    cmp al, 105

    je Up





    cmp al, 106

    je Left





    cmp al, 108

    je Right



    jmp mouse



    Right:

        add dl, 1

        call SetCursor

        jmp mouse

        ret



    Left:

      sub dl, 1

      call SetCursor

      jmp mouse

      ret



   Up:

     sub dh, 1

     call SetCursor

     jmp mouse

     ret



   Down:

      add dh, 1

      call SetCursor

      jmp mouse

      ret



   SetCursor:

       mov ah, 02h

       mov bh, 00

       int 10h

       ret

Bootloader (a little part of it):

%include "stage2info.inc"



STAGE2_LOAD_SEG  equ STAGE2_ABS_ADDR>>4



.stage2_loaded:

    mov ax, STAGE2_RUN_SEG      

    mov ds, ax

    mov es, ax

    jmp STAGE2_RUN_SEG:STAGE2_RUN_OFS



TIMES 510-($-$$) db  0

dw 0xaa55

Why cursor doesn't moves vertically on real hardware but does on a virtual machine?
I tried to change the keys but nothing, same.
Why the code doesn't work on real hardware?
Is my code wrong?

Issues and comments:

• To check for the arrow keys you need to look at the scancodes in AH, not the ASCII characters in AL. Scan codes are 0x50 for down, 0x48 for up, 0x4b for left, and 0x4d for right


• You don't initialize DH and DL before entering your mouse loop. Retrieve the current coordinates with Int 10h/AH=3h before entering the loop


• You don't test the bounds going off the top, left, right, and bottom edges of the screen so if the cursor goes out of bounds unexpected things can happen


• You have unnecessary ret instructions after jmp mouse that can never be reached.


• You can use INC and DEC instructions to add or subtract one from a register rather than using ADD and SUB with a value of one.


• For people viewing the question, the bootloader being used is a template I put together in this Stackoverflow Answer.

This code should work:

%include "stage2info.inc"

ORG STAGE2_RUN_OFS



BITS 16



MAX_ROW equ 25                  ; 80x25 screen extents

MAX_COL equ 80



mouse:

    mov ah, 3                   ; Get cursor BIOS call

    mov bh, 0                   ; Page number is zero

    int 10h                     ; DH and DL will be set to current coordinates.



    mov ah,0h

    int 16h



    cmp ah, 0x50

    je Down



    cmp ah, 0x48

    je Up



    cmp ah, 0x4b

    je Left



    cmp ah, 0x4d

    je Right



    jmp mouse



    Right:

      inc dl

      cmp dl, MAX_COL           ; Test for right edge.

      jl right_bound_ok

      mov dl, MAX_COL-1

    right_bound_ok:

      call SetCursor

      jmp mouse



    Left:

      dec dl

      jge left_bound_ok         ; Test for left edge (<0?)



      mov dl, 0

    left_bound_ok:

      call SetCursor

      jmp mouse



    Up:

      dec dh

      jge up_bound_ok           ; Test for upper edge (<0?)



      mov dh, 0

    up_bound_ok:

      call SetCursor

      jmp mouse



    Down:

      inc dh

      cmp dh, MAX_ROW           ; Test for bottom edge

      jl down_bound_ok

      mov dh, MAX_ROW-1

    down_bound_ok:

      call SetCursor

      jmp mouse



    SetCursor:

      mov ah, 02h

      mov bh, 00

      int 10h

      ret