From: Eric Jacobs <no AT no DOT no>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: [Q] Inline Assembly
Date: Mon, 30 Jun 1997 12:40:40 +0000
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John Eccleston wrote:
> 
> Hi All,
> 
> I am having little difficulty trying to copy my double buffer to
> video memory and I was just wondering if anyone could put me out of my
> misery and tell me why the following code gives me a striping effect on
> the screen.
> 
> -----> Cut here <-----
> void vgaBlitBuffer(BYTE *buffer)
> {
>    int
>       selector = _dos_ds;
> 
>    /* Synchronise with vertical retrace to avoid flicker */
>    while ((inportb(IST1_ADDR) & 0x08) == 0); /* Wait for vertical retrace */
>    while ((inportb(IST1_ADDR) & 0x08) == 8); /* Wait for end of retrace */
> 
> #if 0
>    /* Blit the double buffer */
>    movedata(_my_ds(), (int) buffer, _dos_ds, 0xA0000, 320 * 200);
> #else
>    asm("movw %%ax, %%es\n\t"
>        "movl $0xA0000, %%edi\n\t"
>        "movl $16000, %%ecx\n\t"
>        "cld\n\t"
>        "rep\n\t"
>        "movsl\n\t"
>        : /* no output registers */
>        : "a" (selector), "S" (buffer)
>        : "%eax", "%esi", "%edi", "%ecx");
> #endif
> }

Your mov's are backwards! It's   mov dest,src

Also, I believe there is an inline function in movedata.h called _movedatal
that is exactly what you want here. You call it the same way as movedata
except you specify 16000 (longs) as the count instead of 64000 (bytes).

-ej