[Coco] CoCo3FPGA, FPGA Development, and GIME replacement

[John Kent]

On 6/07/2011 9:40 AM, Mark McDougall wrote:
>
> 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,
>

A Bressenham line drawing routine is not hard to do. Area fill is 
probably not that hard either. To do it in the CoCo3 memory would need 
something similar to DMA to access the shared memory and would have to 
be designed for the different graphics modes.

John.

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