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

Sean Caron scaron at
Tue Jul 14 12:49:29 CDT 2015

That's an interesting argument against using FPGAs in this sort of
application; definitely food for thought. That said, from my (admittedly
limited hobbyist and academic exposure) to FPGAs, I would expect the bulk
of of whatever's being implemented would be fairly device-agnostic ...
certainly you might have to go and recreate your "project" in the newer
version of whatever toolchain you're using for design, and you might have
to go and remap all your pads for pins in and out of the device but I'd
expect you could just take the bulk of the VHDL or Verilog implementing the
CPU and any emulated peripherals on-FPGA and basically copy and paste that
right in, no? I could see some minor tweaks being required, but certainly
nothing on the order of doing the original design.



On Tue, Jul 14, 2015 at 1:17 PM, Chuck Guzis <cclist at> wrote:

> I'm missing something in this discussion, I think.
> HDL's (take your pick) are just programming languages like FORTRAN or C
> with different constraints.  What's the point of going to all the trouble
> of doing an FPGA implementation of a slow old architecture, when pretty
> much the same result could be obtained by running a software emulator?
> Neither accurately reflects the details of the real thing--and there will
> always be the aspect of missing peripherals.
> Perhaps the worst aspect of using FPGA is that this is a rapidly moving
> field, so that the part you used to do your implementation 10 years ago
> will no longer be available.    I've done a few designs using 5V CPLDs
> (XC95xx series) not *that* long ago.  Now they themselves are quaint
> examples of obsolete hardware.  You can't win.
> You can move software-only simulators quite easily, but I'm not as
> sanguine about FPGA designs.
> And you still don't have the peripherals.  I suppose one could emulate a
> Univac Solid State machine in FPGA, but what would one do about the
> all-important drum coupled to the card reader and printer.  Has anyone
> rolled out a design for a DIY 1403 printer?
> I've run the Cyber emulator as well as various SIMH emulators from time to
> time, but it's just not the same as the real thing--it's not even remotely
> the same.
> --Chuck

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