[Coco] CoCo monstrosity |was: [OT] Atari 8-bit video card

[Mark McDougall]

On 18/06/2013 4:52 AM, Steve wrote:

>> In theory someone could make a bridge between the CoCo and a PCI-E slot
>> and you could command a modern video card with the CoCo driving a modern
>> monitor. It would be an interesting experiment, albeit something that's
>> probably not at all practical. -Mike
>
> It's just not practical, but shouldn't even be talk about since it could
> never be made to work.
>
> I've seen some dream-up "pie in the sky" "theories" on stuff to interface a
> coco to, but this one takes the cake.

While you speak the truth, not everyone on this list has the technical 
background to understand why this is such an impractical idea. So perhaps 
some explanation would be in order, in order that they may learn something, 
rather than outright dismissal.

And it should be mentioned that while grossly impractical, it is entirely 
possible.

However, there are several reasons why this would be so impractical. 
Firstly, PCIe bus rates are so high that it would be akin to filling a 
swimming pool through a straw. Secondly - and the very reason why graphics 
cards use a high bandwidth bus - is that the amounts of memory on the cards 
that require moving data around for a display would take the poor Coco a 
month of Sundays to render a single frame. Sure, you could use simple 
lower-resolution 2D frame buffers for the Coco, but it's infinitely more 
practical to spin your own VGA controller in a CPLD/FPGA (which is what has 
been done with the Atari board), or use a COTS CRTC chip.

This thread has spawned a few ideas, both of which have been mentioned 
before, and both of which are equally valid IMHO.

I've considered a VGA cart in the past; snooping the bus to render a display 
via a VGA connector is definitely an option. There'd be a few nigglies to 
consider I'm sure, but I'd imagine it doable. It has been done on the Apple 
II (Carte Blanche), for example, and I'm sure on others as well.

And it goes without saying that a GIME replacement is a great option too 
(James?).

And I don't see why both of these options couldn't offer enhancements, like 
higher resolution (but let's not get silly), more colours and a 
tilemap/sprite system.

Regards,

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