[Fpga-synth] Using Actel Fusion FPGA's to emulate Curtis chips?

[Joe Rounceville]

Hello everyone,

I'm new to this list, and a complete newbie to FPGAs, so I'm guessing what I'm about to ask is so complicated maybe nobody will even venture a thought, but I figure I might as well ask.  I've observed that there are some really sharp folks on this list.

As you probably know, the Curtis CEM chip series has become increasingly NLA, with little caches of NOS appearing from time to time, but no long term solution exists.  People are resorting to cannibalizing otherwise working (or nearly working) synths in order to make money off the CEM chips.  (http://cgi.ebay.com/OBERHEIM-OB8-Spares-Parts_W0QQitemZ170290424178QQcmdZViewItemQQptZKeyboards_MIDI?hash=item170290424178&_trksid=p3286.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50)
These chips are selling for nearly $50- $100 each in some cases (An Oberheim OB8 has 44 such chips, so you can see why people are cannibalizing).  With Curtis out of business, the prospects of ever getting OEM replacements is gone, many of the synths that represent the early days of polyphony and the golden age of the monophonics are built around these chips, and it's a shame to see them getting stripped to support an ever declining set of working synths.

So, here's the million dollar question.  First, would it be possible to reverse engineer these:  

http://www.synthtech.com/cem/cemdata.html

using the Actel Fusion hybrid digital/analog FPGAs, and end up with something that was plug compatible with say the CEM3310, CEM3340, CEM3391, etc. chips?  I'm guessing the answer is a tentative "maybe...but", so the corollary question is:  "What is the relative difficulty of doing something like that?"  In other words, say you're somebody like me with a strong software engineering background (including C and assembler on various platforms), a little embedded system development experience (Nintendo DS game dev, old 8-bit 6502 stuff, etc.), and you've built a few DIY synth projects (PAIA Fatman, Midibox, etc.)... is it even conceivable for someone like me to be able to take on a project like that?  Clearly my strong suit is software and digital, and I'm wondering if the analog + hardware gap is too big to bridge... Let's say I wanted to start with the CEM3340 (VCO)... where would I start?

As I say, I'm a complete and utter newbie at FPGAs... I know enough to know that there are 3 or 4 kinds of FPGAs, with the SRAM kind being most common... I know that these hybrid analog/digital FPGAs like the Actel Fusion are relatively new, and prior to these you'd probably use some kind of attached ADC/DAC to achieve what I'm talking about.  I know that you can build FPGA solutions with soft cores of various preconfigured "chips" like microprocessors... I know that you use Verilog or VHDL to configure the FPGA, and there are tools that make that easier... and beyond that I'm a newbie.  Anybody interested in helping me get acclimated?  Maybe point me to a crash course, or walk me through your own path?  And of course, I'd love everyone's thoughts on the viability of the project idea.

Thanks,

Joe Rounceville
Pleasant Hill, Iowa, USA

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