[rescue] Screw (software) emulators!

[Ken Hansen]

James,

Thanks for the answers - I always appreciate your insights...

It would be an interesting toy, if priced in the WTF price range of $100 -
$150, with some reasonable OS...

I noticed the software emulation site I listed before had some form of IBM
1401 emulation - that would be interesting to look at too...

Ken

----- Original Message -----
From: <james at foonly.com>
To: <rescue at sunhelp.org>
Sent: Monday, August 06, 2001 8:20 PM
Subject: Re: [rescue] Screw (software) emulators!


> On Mon, 6 Aug 2001, Ken Hansen wrote:
>
> > I *love* it - I wonder how the speed compares to the original, and I
wonder
> > if it would bepossible for him to market such a "clean room" copy?
>
> It's clocked at 8MHz, so if he kept the cycle times reasonable (haven't
> looked at his VHDL in detail) it should be one of the zippiest -8's.
> Marketing it would almost certainly be possible as it doesn't look like
> anything proprietary was infringed upon.
>
> > Could one fothe more knowledgeable folks out there explain for us
"regular
> > folk" how hard it is to emulate a complete system (CPU, etc) in a FPGA
> > (Field Programmable Gate Array)? It seems very rough, but then again,
> > someone appraching the "problem" of building a PDP-8 with the benefit of
> > modern tools has a distinct advantade over the original designers...
>
> It's easier than designing a new CPU in silicon.  Depending on how low
> level you get, it can be as easy as writing a software emulator.  Banging
> out raw VHDL frequently takes more work but can give you a faster, tighter
> finished product.
>
> He could have combined the CPU, IOU and SRAM into a larger FPGA if he had
> wanted to.  There are plusses and minuses to this, but it would have made
> the board much simpler physically.  2-layer PCB's do not mean that
> through-hole makes more sense.  Surface mount would have worked fine for
> this application and enabled the use of a larger chip.
>
> Since the RAM can be clocked much higher than 8MHz, a shared-memory SMP
> PDP-8 could be built fairly easily by clocking the RAM accesses faster and
> interleaving requests from each CPU.
>
> -James
>
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