[Coco] General question for the fpga guru's out there

[Mark McDougall]

On 2/01/2013 5:15 AM, T. Franklin wrote:

> The FPGA boardsused for CoCo emulation are simply ?evaluation?boards that
> MFG?s sell for Engineers and Schools to use as a teaching tool.

The eval boards have a range of connectivity options and unfortunately they 
tend to all lack in at least one area; if it's not colour resolution, or RAM 
type, it's SD card etc.

> Hemost common FPGA used to emulate the CoCo isthe Altera DE-1 board.

The Minimig (Amiga), OCM (MSX) & Zet (8086 PC) (as well as a few 
lesser-known) projects all target the DE1 board, so it's going to remain 
popular for a while yet. The DE1 has been superceded by boards with larger 
devices; it's a pity because it was unique in that it had 24-bit VGA, Flash, 
SRAM, SDRAM and SD slot. It also had two 40-pin IDE expansion connectors 
which, whilst not strictly 5V tolerant - could be used to interface to 
custom peripherals.

> The companies thatmake these boards are in the business
> of making and selling FPGA?s.

Agreed, they're simply not that interested in moving eval boards. The 
revenue would even register as a blip on the radar - they may even be making 
a slight loss.

The problem I see with the MCC-216 is two-fold; firstly, it is a hobbyist 
build made to be as cheap to produce as possible, which means little or no 
expansion I/O. So it'd very difficult and/or impossible to add legacy 
peripherals. Secondly, there's always a possibility that they'll disappear 
overnight.

One issue I see with the MCC-216 regarding Coco3FPGA is that it doesn't have 
SRAM, which Gary uses for main memory. So he'll need to add SDRAM support - 
with the inherent latency issues - to his design, and the Coco becomes even 
less 'cycle accurate' (not that the 6809 core is atm anyway).

IMHO the DE1 is still your best bet. I'm not sure about the later TerASIC 
boards, but the DE2 at least is somewhat backwards-compatible, so any design 
for the DE1 is trivial to port to the DE2. I suspect that's true for the 
DE2-70 and the DE2-115 - they at least look very similar.

I've mentioned this before; my colleague & I were working on a Coco 
motherboard replacement project before rather sad circumstances drew that to 
a close. However, if I ever found myself with enough spare time, I'd 
certainly like to resurrect it. The emphasis would be on providing an 
enhanced Coco experience with full legacy peripheral connectivity, and a 
drop-in replacement for a Coco motherboard. It wouldn't be cheap, but it'd 
be cool! Of course, I make no promises and it could well be 5 years away - 
if ever.

Regards,

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