On Thu, 14 Dec 2000, Josh G wrote:
> I have a question- does plex cache prescanned pages? perhaps cache
> them after converting some things? I mean 90% of all graphics port
> code will be something like:
>
> mov al,3c0h
> out al,ah
would be
mov dx,3c0h
out dx,al
on i386.
Anyway, the problem with planar modes is the memory.
VGA planar memory is quite complicated and you usually need to read from
the address before you want to write to it, in order to load the latches
which can preserve the bits you don't want to change: like this
mov ax,0a000h
mov es,ax
mov cx,640*480/8
xor di,di
mov al,bit pattern
cld
label: mov ah,es:[di] ;load 32-bit latch register which contains all
bytes at the four planes under es:[di].
ah is just dummy.
stosb ;what ends up in memory is a function of al,
the latch and values in I/O registers. I've
optimized this specific function.
loop label
You _have_ to cache this or do cpu-emulation to make this fast, but
_cannot_ execute this natively, because VGA memory is basically one large
piece of MMIO (this comment about MMIO is in the plex86 white paper
somewhere). I'm just not familiar enough (not at all) to know how it works
right now.
Bart
