14 Jul
2015
14 Jul
'15
10:32 a.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Chuck
Guzis
Sent: 14 July 2015 18:17
To: General at classiccmp.org; Discussion at classiccmp.org:On-Topic and Off-
Topic Posts
Subject: Re: Reproducing old machines with newer technology (Re: PDP-12 at
the RICM)
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?
I don't think this is true. Most of the software simulators don't run at anything
like accurate speed ...
Neither
accurately reflects the details of the real thing--and there will always be the
aspect of missing peripherals.
I believe that you can get much closer with an FPGA...
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.
That is very true, but there again the same can happen with Software. The Pegasus
Simulator I use was written in TurboPascal and has kludges to get the speed right that
just don't work on a modern PC
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.
See Above
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?
When I have finished the Calcomp Plotter....
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.
I have used Hercules with a real 3270. Its not bad but Laurence Wilkinson's 360 in
FPGA wih a real Selectric Typewrite is much better:-
http://www.ljw.me.uk/ibm360/Saga.html
--Chuck
Dave