[Coco] What would a CoCo successor have to have as a minimum?

Mark McDougall msmcdoug at iinet.net.au
Sat Nov 20 08:48:50 EST 2010

On 21/11/2010 12:16 AM, Frank Swygert wrote:

> The main issue is ROM and FPGA space. The CC3 can only access so much ROM,
> and to make it compatible you have to have some of the old ROM code.

Gary Becker's Coco3FPGA can only access so much ROM.

An FPGA can access an arbitrarily large ROM/RAM.

> On the emulation side it's not as big an issue, but on the FPGA side the
> bigger the FPGA has to be (and higher cost) to have all the extras in it.
> This is something the two systems could diverge in though -- CoCo 1/2
> compatibility in emulation, not in FPGA.

I think people are overestimating the resource requirements of the FPGA. 
Things don't necessarily scale like some people imagine. It's generally 
more-so the resources off-chip that are going to be more expensive.

> The emulation method could just have a menu option to
> switch to CC1/2 mode, but that might require a re-boot.

Yup, that is probably most likely.

> If it were USB, it would have to have a nice abstraction layer, as USB
> is a right pain to program for, if memory serves...

Depends if you're the host or the device, and which device you choose.

> Exactly!! There has to be some kind of floppy emulation if not a physical
> drive. This could be a problem with FPGA real estate, and may be another
> diverging point -- FPGA with real floppy, emulation with an emulated floppy.

Floppy emulation does not require a lot of resources. Look at Minimig, which 
runs on the DE1. It does twice what Coco3FPGA does. It has twice as many 
processors, much better graphics, floppy emulation, etc.

And the DE1 has quite a small FPGA for modern day standards.

> The main issue is that we really do need the two systems to be compatible,
> 100% if possible. So what limits the FPGA version will also limit the
> software version and vice-versa. That's the only way to ensure they are
> compatible with each other.

Or we specify "must have" and "would be nice to have" requirements that 
provide a lowest common denominator for cross-compatibility.


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

More information about the Coco mailing list