On Wed, 25 Oct 2006, Mike Pumford wrote:

> Maybe a red herring. All the VESA specs I can find suggest that 0 borders(VESA
> calls them margins as you guessed) are okay as well. Based on the fact that
> the monitor is locking on to the mode and reporting the horizontal and
> vertical refresh rates I would expect for the mode I think these vidc
> registers correct. It looks more like the transfer between VRAM and VIDC is
> not being synced properly.

The VIDC20 data sheet does indeed allow zero border widths, and the Risc 
PC TRM doesn't suggest that the IOMD uses the border for anything.

I've been experimenting to try to work out what doesn't work at the 
moment.  I'm a little limited by the fact that  my Risc PC only has an 
AKF50 attached to it, so 1024x768 is out of reach.  At lower resolutions, 
it looks to me like a current GENERIC kernel now behaves the same as a 
netbsd-4 RPC_WSCONS kernel from before I made any serious changes.  What I 
see is:

8bpp 640x480: basically correct

8bpp 800x600: characters seem to have left and right halves swapped.  
Maybe slight fuzziness.

16bpp 640x480 and 800x600: basically correct

32bpp 640x480 and 800x600: disaster.  Left-hand half of screen has a mess 
of stretched , overlapping characters.  Right-hand half is full of 
horizontal stripes.  Everything is flashing unhappily.

One thing I wonder about your configuration: are RISC OS and NetBSD using 
the same refresh rate?  I can imagine NetBSD picking a higher one that 
your VRAM can't keep up with.  Are you using an explicit MONITOR or the 
built-in video-mode database?

-- 
Ben Harris                                                   <bjh21@NetBSD.org>
Portmaster, NetBSD/acorn26               <http://www.NetBSD.org/Ports/acorn26/>