[Coco] [Fwd: Re: CoCo 3 FPGA? (Really long message)]

[Mark McDougall]

> From: Becker, Gary <Gary.Becker at amd.com>

> As I have already mentioned, I have no capabilities to adapt floppy
> drives into the system. 

I'm currently working on a (Commodore 64) 1541 implementation in an FPGA,
that will interface to some sort of external storage media. I have also,
in the past, done a simple WD1793 implementation that interfaces to serial
flash.

My intention is to provide 'sub-cores' if you like of disk controller and
disk media interface IP that can be chopped-and-changed to provide a
variety of options for various 8-bit computers.

Interfacing to a real floppy is also on my list...

> This pulse stream runs fast
> enough where a simple low pass filter should be able to convert it to
> audio. This filter is the additional circuitry needed. I will be
> building prototype circuitry soon for testing.

I've had reasonable success in the past with a Sigma-Delta DAC and
external RC low-pass - not that I've been concerned with high-fidelity
output! ;) May I suggest you package the DAC at the top-level, to expose
the 6-bit digital stream on other platforms such as the DE1/2 and/or
NanoBoard which have on-board audio DACs.

> I am sorry to say, I have no plans to support the standard CoCo
> joysticks. This joystick uses a DAC to sense the position of the
> joystick. As I mentioned in the last paragraph, the response was
> unacceptable in my past tests. 

I'm surprised you didn't get acceptable results - or did you stick with
the resistor-ladder ADC? I would think there's plenty of cheap ADC chips
out there that would be more than adequate for the task?

> The different type of joystick will be software
> compatible with the original joystick, but with only three positions
> vertical, up, middle, and down, and three positions horizontal, right,
> middle, and left. 

That's OK for games that are, in effect, using the joystick as a digital
joystick, but I suspect not suitable for all games?!?

> What I would prefer
> not to happen is someone package this system up for mass market
> consumption similar to the $25 arcade games based on the Commodore 64
> platform that you see at Wal-Mart.

With all due respect, I think the C64-on-a-joystick market is _way_ larger
than a Coco-on-a-joystick market. In any case, an FPGA-based design is
simply not economical - it would have to be an ASIC design and you're
talking _big_ bucks there.

IMHO you should be more concerned that someone will package a 'games
development system' or similar like the XGameStation, and bundle your Coco
design with it.

Regards,

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