Re: Bad video output on RiscPC

On Sat, 28 Oct 2006, Mike Pumford wrote:

> 60Hz is well within both the VRAM capabilities, assuming we are really
> operating at 8bpp, and the capabilities of my monitor. Everything flashing
> about unhappily is a very good description of the problem at 1024x768 although
> I don't get stretched characters.

Having lent the LCD monitor from my NC to my Risc PC, I managed to 
reproduce your problem, and then solve both it and the problem I was 
having with 800x600x8bpp.  The problem was that NetBSD was chosing the 
video FIFO preload based on the display width rather than on the video 
bandwidth, so the FIFO overflowed in wide, low-bandwidth modes.  This 
problem actually existed before my changes, but the mode-selection 
algorithm was different then, and would chose 1024x768x70 (which didn't 
show the problem) in preference to 1024x768x60 (which did).

I've fixed the problem in revision 1.30 of vidc20config.c by not trying to 
pick the best FIFO preload and just picking a safe value.  This might 
cause problems if you use a very high-bandwidth mode on a machine with 2MB 
VRAM.

There's still a problem with 32bpp modes, but I don't think it's a new 
one.

-- 
Ben Harris                                                   <[email protected]>
Portmaster, NetBSD/acorn26               <http://www.NetBSD.org/Ports/acorn26/>