[Coco] Multi-Processor 6809 Computer System

[Mark McDougall]

On 1/05/2013 6:51 AM, Bill Gunshannon wrote:

>> Better graphics with more color and resolution means more memory required.
> In the graphics cartridge.  Dedicated to the graphics.  Doesn't take
> away from the memory availabel to the processor.

If you don't want to increase the graphics memory footprint in the CPU 
memory space, then you need some sort of scheme for transferring graphics 
data to/from the memory on the cartridge. This means that a lot of graphics 
operations will actually be _slower_; even more-so with increased resolution 
and colour depth.

>> And this to still be pushed by the same 1.78Mhz CPU?
> No, actually the COCO CPU does less as it doesn't have to compute
> things like graphics vectors.  Graphics processor in the cartridges
> does that freeing up the COOC CPU to do more of the things it does
> best.

You can throw around the concept of 'graphics co-processor' but I'm finding 
it difficult to imagine exactly what sort of co-pro is going to help the 
Coco. Firstly, it doesn't alleviate the problem of getting data into the 
graphics memory which, as I mentioned above, is going to be slow. Secondly, 
we're talking 2D graphics here (unless you're *really* ambitious, and I 
think that's unrealistic), and there's not much 'co-processing' that can be 
done aside from a blit engine (which still requires direction from the CPU). 
Otherwise you can implement tiles and sprites, which actually require less 
CPU power and memory and could be controlled directly from the 6809 IMHO.

Then with a graphics co-pro of course there's a radical departure in the way 
the Coco graphics are handled, which means radically new software for even 
the most basic tasks.

Don't get me wrong, I think the idea of a graphics cartridge is actually 
pretty good - enhanced graphics and VGA output on an unmodified Coco 1/2/3 
is pretty neat! I just don't think it's the answer to the problems that 
you're making it out to be.

Regards,

-- 
|              Mark McDougall                | "Electrical Engineers do it
|  <http://members.iinet.net.au/~msmcdoug>   |   with less resistance!"