From: Thomas,Trevor <trevor.thomas@cdott.com>
  To  : 'ggi-develop@eskimo.com' <ggi-develop@eskimo.com>
  Date: Mon, 17 May 1999 16:19:16 -0400

RE: GGi frame buffer and video memory question

On Friday, May 14, 1999 7:02 PM, Andreas Beck
[SMTP:becka@rz.uni-duesseldorf.de] wrote:
> > hardware: vid card ->Mill II 8 meg (4 visible, 4 upgrade).
> > 		   display ->	20.1 NEC AMLCD
> > images: 1280X1024 8bit
> Hmm - that's very hard. Hmm - AMLCD - does that mean, it's an LCD screen ?

yes..

> > 3. Because the images are not being displayed 100% correct for >3
> > framebuffers does this cause any timing delays?
> 
> No. It's just displayed wrong. The fb driver _thinks_ it has 8M, while 
> it can actually only use 4M. That causes it to allow a 4-frame mode, 
> which actually is more a 3-frame mode with a wraparound after 3.25 
> images.
> 
> What you see when selecting image 4 is its first part (what fits between
> the end of the third image and the 4MB boundary), plus the first
> picture again, when the memory pointer wraps 4MB->0.

hmmm....
that is what I thought I should see however that is not what I am seeing...
it does display all 4 images... like this however... 

				Screen	
----------------------------------------------------------------------------
--------------
|	last 1/4		| Start of image -----------------------> up
to 3/4    |	
|	of image	|
of image     |

hope that bad drawing helps...
	
I thought that it should wrap around after 3.25 images and display a part of
the first image again...
It does however display all 4 images the same as described above..... This
is weird I know because somehow it is accessing the nonvisable memory and
displaying from it...just not correctly... any ideas?? 

Thanks

Trevor


Trevor Thomas
Computing Devices Canada
Advanced Displays Group
Phone: 613-596-7489
email: trevor.thomas@cdott.com