Reproducing old machines with newer technology (Re: PDP-12 at the RICM)

[Paul Koning]

> On Jul 13, 2015, at 8:35 AM, Jay Jaeger <cube1 at charter.net> wrote:
> 
> Another alternative would be to build a machine up from a Field
> Programmable Gate Array (e.g., the Digilent Nexys2 FPGA development
> board).  I recently completed an effort doing that for a 12 bit machine
> we designed and built in a logic/computer design class from racks of
> logic interconnected using IBM unit record plug boards in 1972.
> 
> I am going to attempt to do the same for IBM's 1410 computer - a really
> big effort.

That’s been done for all sorts of machines, of course; the PDP-11 comes to mind.

One question would be what design approach you’re using.  A behavioral model is one option; that’s roughly SIMH in an FPGA.  And just like SIMH, the model is only as accurate as your knowledge of the obscure details of the original design.  Depending on the quality of available manuals, this accuracy may be rather low.  (For example, building a PDP-11 model if all you have is a Processor Handbook may not be accurate enough.)

A different approach is to reproduce the actual logic design.  FPGAs can be fed gate level models, though that’s not the most common practice as I understand it.  But if you have access to that level of original design data, the result can be quite accurate.

I’ve done a partial gate level model of the CDC 6600, working from the wiring lists and module schematics.  It accurately reproduces (and explains) quite obscure properties of the peripheral processors, things that aren’t documented anywhere I know of other than in programmer lore.  It also yields a large model that simulates very slowly...

	paul