frontbuffer equ 0A000h
backbuffer equ 09000h
macro exitDos {
        setmode 0003h
        mov ax,4C00h
        int 21h
}
macro setmode n {
        push ax
        mov ax,n
        int 10h
        pop ax
}
macro clrscr color {
        mov al,color
        call clearscreen
        call swapBuffers
}
macro checkKey { 
        mov ah,11h
        int 16h
}

use16
org 100h

setmode 0013h

mov bl,0
start:
clrscr bl
inc bl
checkKey
jz start

exitDos

swapBuffers:
        mov cx,16000 ; fixed
        mov di,backbuffer
        mov si,frontbuffer
        mov ds,di ; push/pop better?
        mov es,si
        xor di,di
        xor si,si
        vBlankBegin:    ; wait for vertical retrace
                mov dx,03DAh
                v1:
                in al,dx
                and al,08h      ; 00001000b
                jnz v1                  ; bit8 == 1,still in vertical blank 
                v2:
                in al,dx
                and al,08h
                jz v2                   ; bit8 == 0,out of vertical blank,wait for this to finish
        vBlankEnd:              ; entered v.blank again,start to copy
        rep movsd               ; ds:si -> es:di, find a faster way(unroll loop,fpu?)
        ret
clearscreen:
        mov di,backbuffer
        mov es,di
        xor di,di
        mov cx,64000
        rep stosb ; al -> es:di , es=backbuffer
        ret

;backbuffer dw 09000h
;frontbuffer dw 0A000h
    

to implement double buffering example

backbuffer equ 09000h
    

swapBuffers:
    

        mov cx,64000
        rep movsd               ; ds:si -> es:di, find a faster way(unroll loop,fpu?)
    

        mov cx,64000
        rep stosb ; al -> es:di , es=backbuffer
    

if i'm not wrong, a com file is limited to use 64k,so there's no way i can allocate enough memory.

in one of the posts,i saw a nice program that utilizes 09000h,i thought it's ok to use it as a base for backbuffer

*method to return clock rate
*use the timer and clock rate,figure out how many cycles it takes for a vblank
*loop for that many cycles
    

; assuming esi, edi hold the buffer's and ecx has been set move one paragraph at a time.

; if you use a far call to blt the cache lines will be cleared.

    align 16                ; ensure that the whole routine read into cache
blt:
    mov eax, [ds:esi + 00]  ; - v pipe
    mov ebx, [ds:esi + 04]  ; - u pipe
    mov ecx, [ds:esi + 08]  ; - v pipe
    mov edx, [ds:esi + 12]  ; - u pipe
    mov [ds:edi + 00], eax
    mov [ds:edi + 04], ebx
    mov [ds:edi + 08], ecx
    mov [ds:edi + 12], edx
    add esi, 16
    add edi, 16
    nop                     ; not to sure how much padding needed here
    loop blt                 ; loop should be at the end of a 16 byte boundry
    ret                     ; 4 or 8 would do ok though
; if you use the MMX registers you could move 4 paragraphs at a time.    

I think its safe to assume

BLA.EXE crashed at sdjhsjfhsd:sdjhdjf with illegal instruction 
eax=dskfjdlf 84843 34587894 00000 bla bla bla bla ...
    

that most CPU's have MMX theese days

suffisticated graphics lib would time the WaitRetrace period for a few seconds useing a high resolution timer to measure

good article on programming the system timers

What about porting it to MMX. I think its safe to assume that most CPU's have MMX theese days. Even a P-166.

but DOS code should work down to 8086 or 80386 at least.

Should'nt I expect more from it ?

I would expect silent playing ... rather than "No SoundBlaster"