From: Alexander Larsson <alla@lysator.liu.se>
  To  : ggi-develop@eskimo.com
  Date: Sun, 05 Jul 1998 19:58:35 +0200

Re: kgicon difficulties |-< (and new tarballs |->)

> Jon writes:
> 
> >  	Today did NOT go as smoothly as yesterday did.  I am having
> >  problems getting 4bpp modes to work right.  The 4bpp routines in fbcon
> >  have some major problems, it seems.  The foreground color is hardwired to
> >  15, which I found and patched after much head-scratching, but there is
> >  still a very strange problem with garbled fonts which I cannot for the
> >  life of me track down.  
> 
> AFAIK (and that aint far), fbcon-cfb4.c is for "4 bit packed pixels"
> which is like the code in lib/libggi/default/linear-4/*, whereas VGA 4
> bit mode is a weird thing called "ModeX" and needs code like the stuff
> in kgi/lib/libggi/IBM/*.
 
 VGA 4-bit mode is not Mode-X. Mode X is a mix of MCGA 256 color mode and the 
standard 4-bit vga mode with latches to access the 4 bitplanes.
> 
> Also, is the 640x400x4bit mode banked ?  It must take up at least 128K,
> but the window at A0000 is usually only 64K (again AFAIK, which aint
> much).
 No, 600x400x4 is not banked. At least not in the normal sense. All 4 
bitplanes are mapped to the same place in memory and a mask that you can set 
decides which bitplane is written to. Soo, it is not 4bit packed but 
essentially a 4 bitplane model where the 4 bitplanes are reached in a bit of a 
strange way.

/ Alex