I'm having trouble with drawing squares on the x86 assembler using the XGA 8-bit linear frame buffer. I'm suppose to draw a large square containing a grid of smaller 12x12 squares using my own functions and this is what I have so far:
[SECTION .text]
;----------------------------------------------------------------------------
; code belongs in this section starting here
mystart:
mov ah, 0fh ; BIOS function - get current video mode
int 10h ; call BIOS video interrupt
mov [vidmode], al ; save the current video mode
mov eax, 4f02h ; SVGA function - set SVGA video mode
mov ebx, XGAMODE ; select XGA video mode
int 10h ; call BIOS video interrupt
mov ecx, 12
mov eax, xPos
sqrver:
push ecx
mov ebx, yPos
mov ecx, width
mov edx, eax
push eax
mov eax, ebx
mov ebx, XGAXRES
mul ebx
pop ebx
add eax, ebx
vloop:
mov byte [fs:eax], 15
add dword eax, 800
dec ecx
jnz vloop
add dword eax, 5
pop ecx
loop sqrver
mov ecx, 12
mov ebx, yPos
sqrhori:
push ecx
mov eax, xPos
mov ecx, width
mov edx, ebx
push eax
mov eax, ebx
mov ebx, XGAXRES
mul ebx
pop ebx
add eax, ebx
hloop:
mov byte [fs:eax], 15
inc eax
dec ecx
jnz hloop
add dword ebx, 5
pop ecx
loop sqrver
mov ah, 1 ; select DOS function - input character
int 0f1h ; call OS function to wait for key press
mov ah, 00h ; BIOS function - set video mode
mov al, [vidmode] ; restore the old video mode
int 10h ; call BIOS video interrupt
ret
;----------------------------------------------------------------------------
[SECTION .data]
;----------------------------------------------------------------------------
; all initialized data variables and constant definitions go here
XGAMODE equ 4103h ; XGA video mode code (w/ linear addr bit)
XGAXRES equ 800 ; horizontal resolution of XGA screen
XGAYRES equ 600 ; vertical resolution of XGA screen
xPos db 300
yPos db 50
width equ 400
;----------------------------------------------------------------------------
[SECTION .bss]
;----------------------------------------------------------------------------
; all uninitialized data elements go here
vidmode resb 1 ; the old video mode
When I try to run it, only a few lines appear on the screen and the program lags for a bit before exiting...
Any help would be appreciated.
Unsolved 
