Subject: Re: Minimal CP-M SBC design
From: "Chuck Guzis" <cclist at sydex.com>
Date: Sun, 18 May 2008 10:31:45 -0700
To: cctalk at
classiccmp.org
Date: Sun, 18 May 2008 10:09:45 +0100
From: Gordon JC Pearce
Aha, I disagree. You can't get at the
innards of the 6120 at all,
because it's a chip. If you want to get at the innards of an emulator
then you can, although how accurately the emulator models the logic of
the -8 might be an issue (my emulator doesn't model it at all, but
largely does its own thing).
I was going to reply along the same lines, but I felt it might not
have convinced my audience. Back in the old days of 22Nice, we added
an emulator feature that allowed a user to write his own port-mapping
code and include it with each program, allowing each individual
program to have its own simulated peripherals, if desired.
This was no accident or a "feature for feature's sake". A customer
was replacing a controller on a large piece of CNC machine tooling
(they made trailers for large trucks). Communication with the
machine was largely RS-232, so that was no problem with the PC, but
the controller application directly manipulated a UARTs registers.
We rolled an emulator overlay for the UART that functionally mapped
the program's accesses to the PC's 8250-type UART. It worked right
on the first try and the customer was happy for many years--and we
changed not a byte of code in the original program, nor our basic
product.
That's the beauty of emulation--if the original box uses a bizarre
interface or unobtainium chip, you can emulate it. MUCH easier than
trying to do the same in hardware. Modern PCs tend to have
sufficient excess horsepower that you can emulate just about any 80's
era device without impacting performance.
That is the exact reverse case I was refering to. For that case and many
others like it I agree heartily. One of the "sims" I use is VMware under
Linux So I can run them crufy MS OSs without havignto invest hardware
on a daily basis. Doesn't hurt that I can also use it run a sim in
a sim like MyZ80 inside W98se on the fast Linux machine.
But, as I've said, I felt that I wasn't going
to sway the hard-bitten
hardware folks. As you pointed out, the line between hardware and
software is getting very blurry indeed. Cheap, fast,
microcontrollers now give a new spin to tasks that would have
normally been accomplished with a pile of discrete logic and can now
be done with little more than software.
It works for me where it fits. If I want Z80 hardware no amount fo sim
will make me happy but at the same time I may use a sim to build code
for that Z80. As I've done it that way and in reverse and also to solve
the problem of hardware that is unobtaimium.
Where it works, I want to emulate a PDP1, or replace a PDP-11. Where
it doesn't work so well is when I want to run VMS on a MicroVAX with
performance in the NVAX realm.
Maybe time to chance the topic??? This is clearly outside the discussion
of how to make a minimalist CP/M system ( maybe even SBC).
Allison