[Coco] Update on new Coco 3 game engine

[Richard Goedeken]

Thanks for the input Nick.  It's great to hear of your progress.

Dividing the horizontal clock by 2 is a really good idea.  Making this work on 
all Coco 3s could be tricky, because of the 2 different GIME chips.  Is there 
any easy way to tell them apart?  If not, I guess you have to run a timing 
loop with some heuristic to figure out which one you're on.

Do you know what is the minimum audio frequency which can still give decent 
sound?  I don't think there's any low-pass filter on the Coco audio output, so 
it probably will develop aliasing as the sampling frequency goes down.

I agree it would be great if the Coco had at least some audio or graphics 
hardware support.  The thing about Commodore was that it was really a 
semiconductor company, and they sold computers to drive the chip sales.  They 
had some brilliant chip designers; the guy who designed the 6581 SID went on 
to later found Ensoniq, and that was the best sound chip available for many 
years.  The Amiga had a "co-processor" which could be configured to 
automatically set palette colors or other video things on a horizontal scan 
line trigger.  I would love to have things like that on the coco.  Actually, 
with VHDL and FPGA computers now (I have a Turbo Chameleon 64) it's possible 
for a hobbyist to make such hardware mash-ups.  But I love to work on the real 
machines too.

Richard

On 08/13/2013 12:42 PM, Nick Marentes wrote:
> Congratulations Richard. You've nailed it.
>
> Everything you said is totally correct and your logic and understanding of the
> CoCo's capabilities and limitations is spot on.
>
> I am up to the same exact point with my Popstar Pilot game engine. And you're
> absolutely right about the challenges you clearly outlined.
>
> I will soon be posting a new chapter about this very topic on my blog since I
> too have just created the sound routine which is being triggered off the FIRQ
> with interrupts sourced from the TIMER which is itself derived from the
> 15.734Khz clock and divided by 2 to give a maximum audio fidelity of 7.867Khz.
>
> I now need to run optimizations on my code to make it chew up the least amount
> of cpu cycles while still managing the split screen horizontal scrolling and 2
> channel sound sample playback.
>
> If the CoCo only had a sound chip built in as standard!   :)
>
> I look forward to your upcoming game whatever that may end up being.
>
> Nick Marentes
>
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