[Coco] CoCo3FPGA, FPGA Development, and GIME replacement

[Mark McDougall]

On 6/07/2011 9:13 AM, Nick Marentes wrote:

> I would have thought with the advancements in FPGA's nowadays, simulating
> the operations of a 25 year old custom chip should be possible.

In theory Gary's Coco3FPGA does simulate the GIME.

Logic to do graphics, short of 3D processing, is actually relatively 
trivial. It's little more than a bunch of counters, with the right logic to 
get reset at the right time, and fetch the right memory address at the right 
time. Trivial, but fiddly to get right. The GIME would not be difficult.

Consider that we already have the Amiga 500, MSX, Sega Genesis/Megadrive, 
and PC VGA implementations in FPGAs; the GIME is less complex than all of those.

Having said that, it's also one thing to simulate the GIME within the 
context of a custom Coco implementation, and another to design a drop-in 
replacement that interfaces to an external bus and legacy hardware. And not 
very cost effective in an FPGA, that's for sure. A CPLD would be more suitable.

Regards,

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