[gPXE] int 10h problem

[Gene Cumm]

2011/4/1 何闯 <justhechuang at 163.com>:
> Deal all,
> I just tested int 0x10 BIOS interrupt to draw some pictures.
> However, when I coded the follow to enter 640X480 video mode, it seems that
> the actual video mode is 640X100,
> I draw a rectangle with range(0,0, 640, 480) to verify, and it resulted in
> range(0,0, 640,100), about a quarter square of a rectangle.
> And I noticed that 320X200 video mode is OK, and 320X200 == 640X100, is that
> mean my machine can hand only 64000 pixels?
> Can anyone tell me why?
> ///////////////////////////////////////////////////////////////////////////////////////////////////////
> void setvga()
> {
> __asm__ __volatile__ ( REAL_CODE ( "movw $0x4f02, %%ax\n\t"  //ax=0x0012
> here seem stay in the text mode
> "movw $0x0101, %%bx\n\t"
> "int $0x10\n\t" )::);
> }
> void putpixel(int x,int y,int c)
> {
>     if(vediobuf == NULL)
> {
>    vediobuf = (unsigned char*)phys_to_user(0xa0000);  //physic address of
> graphic mode
> }
>     *(vediobuf+x+640*y)=c;
> }
> /////////////////////////////////////////////////////////////////////////////////////////////////////
>
>
> yours,
> soforth

I'd suggest looking at other boot loaders and how they write to the
screen (including Syslinux's vesamenu.c32 and gfxboot.c32).  64,000
sounds like the 16-bit limit of 65,536 per segment.

-- 
-Gene