Message-ID:	<33BD8775.5B02@algonet.se>
Date:	Fri, 04 Jul 1997 16:29:57 -0700
From:	"Adam Skoglund, aka gulgi" <adamskog AT algonet DOT se>
MIME-Version:	1.0
To:	djgpp AT delorie DOT com
Subject:	Re: [Q] Inline Assembly

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
> }
Hello..
The answer is.. movsl movs from ds:esi to es:edi.. not to edi:es..
like this:
  asm("movw %%ax, %%edi\n\t"
      "movl $0xA0000, %%es\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");
I hope it helps..
-- 
/*  -gulgi  adamskog AT algonet DOT se  www.algonet.se/~adamskog    *
 * There's something in the air, makes me go insane          *
 * brings it back to me.                                     * 
 * It's been so long, and alls I have to do, is live along   *
 * Coming coming down, over me				     *
 * Do you want to see, the explosions in my eye 	     *	
 * Do you want to see, the reflection of, how it used to be  * 
 * Beauty lies in the eyes of anothers dreams 	             *
 * Beauty lies in the eyes of anothers dreams \\ Sonic Youth */

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