TTL computing

From: Richard Erlacher <edick_at_idcomm.com>
Date: Wed Apr 10 18:26:49 2002

Well, my recollection may be different from that of others simply because of
when it was formed, but back in the '70's, when bit-slice was becoming quite
popular as a means for creating a computer from hardware of various sorts, the
notion of microcode was used to describe the code for the particular bit-slice
family, often the AMD 2900 series, that was used to create a specific design.
Each instruction in the set attributed to the final target system was
implemented in some number of more simple instructions for the bit-slice
engine.



----- Original Message -----
From: "Thilo Schmidt" <thilo.schmidt_at_unix-ag.uni-siegen.de>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, April 10, 2002 1:02 PM
Subject: Re: TTL computing


> On 10-Apr-2002 Richard Erlacher wrote:
> > Actually, it's all done with software. You simply specify what you want
and
> > tell the software tools to generate it. Part will be implemented in
> I know, but that wasn't point. I tried to explain the difference between
> a "microcoded Design" and a "state machine".
> Or at least what I think it is... ;-)
>
> [...]
> >> On a high level design view it's called state-machine if you draw a graph
> >> and "microcoded" if you write a program.
> >>
> > Today's tools require that you write a program. Whether you do it in C++
or
> > VHDL is up to you, but it's a program either way.

> I think here lies the source of our misunderstanding: I didn't mean a
> program as in C or even VHDL. I didn't even think of any "design tool".
> What I meant (and wrote) was "design view". But I must admit that the word
> "program" wasn't the right choice either... ;-)
>
Well, that's how it's being envisioned for the next generation of development
software, preliminary bits and pieces of which are being tried out on the EDA
community. You write a program/description for a task, and the software
generates the program for the combination of programmable logic and software
that accomplishes the task. It's not defined in advance which functions will
be implemented in hardware/firmware and which will be accomplished strictly in
software, and, in fact, the hardware configuration may change on the fly in
order to facilitate the task. You're right, of course, in that it will take a
while. I remember when the first efforts on VHDL were being touted in the US
defense industry. It took a decade before a useable for m of VHDL was
available and even the versions available today have many quirks not forseen
in the early phases of its development. Of course the FPGA vendors didn't
have their fingers in the pie back then.
>
> A "microcode-program" (in my understanding)can be thought of as a very
> primitive kind of Assembler where you don't have anything but the
> current-state and the inputs.
>
A quick look at the details associated with the AMD2900 series will clear up
whatever gaps there are in your understanding. The tools were not that
primitive, and the instructions, though simple and quick when compared with
single-chip CPU's of the time, were quite effective. The 2900 series was far
and away the most widely used microcoded component series, IIRC.
>
<snip>
>
> While I agree that today no one does such a design by foot but the principle
> is still the same. Even in modern^H^H^H^H^H^H currently marketed CPUs
> like the Pentium4 there are microcoded Areas where you can load updates
> to correct bugs. Intel has learned it's Pentium-Bug-Lesson.
>
> > The "next-generation" tools will take a program in a high-level language
and
> > specify both the hardware and the software from a single source file,
> > including the architecture and instruction set of the CPU if there is one.
> > The software tools will determine which part goes in the FPGA and which
goes
> > on the hard disk.
>
> Hardware-Software-Co-Design is a very interesting research area but
> IMHO it will still take a while till the results hit the market.
>
> bye
>
> Thilo
> --
> The most exciting phrase to hear in science, the one that heralds new
> discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
> -- Isaac Asimov
>
>
Received on Wed Apr 10 2002 - 18:26:49 BST