From: rarachel@prism.poly.edu (Arsen Ray Arachelian)
Date: Thu, 27 Jan 94 12:07:42 PST
To: tcmay@netcom.com (Timothy C. May)
Subject: Re: clipper pin-compatible chip
In-Reply-To: <199401260742.XAA24775@mail.netcom.com>
Message-ID: <9401271953.AA19057@prism.poly.edu>
MIME-Version: 1.0
Content-Type: text


Actually, all you need to know is what pins do what, and what the protocol
of those pins are in terms of their communication with the rest of the
board.

My suggestion was to make a plug in chip that replaced the clipper
chip, however, that chip doesn't need to actually be able to talk to
another clipper chip.  You don't need to disassemble a real clipper
chip to be able to do that.

In order for Uncle Sam to be able to spread the clipper and not
give AT&T any idea about what it actually contains, it has to give
AT&T some interface specs.   It has to provide this information to
any company that intends to use the clipper chip.

Just as you don't need to know the microcode for an Intel 486 to
build a clone, you don't need to know what the guts of the clipper are
to replace it with another chip which doesn't have to be compatible 
with it in terms of communicating with another clipper.  It should
rather only need to communicate with another of its kind be it an
IDEA chip or an RSA chip, etc.

All things considered, a simplified approach at looking at a clipper
would be that of a filter or a pipe.  Data goes in at one end, some
other data goes out the other end.  All you need to do to replace it
with another filter that does a similar (but not identical) job is to
find how the clipper talks to the outside world, which Uncle Sam
has to provide if he wants this chip to take off the ground.  In which
case, once we have specs, we can build an interface to an IDEA chip, etc.
 
Another example: with old old Macintoshes there was a thing called a
"Killy Clip" which looked like a laundry pin that attached over a 68000
CPU and took over its bus to an accelerator card, or some other system
expansion card.  Such things were originally frowned upon by Apple and
mostly Steve Jobs, but they were popular at the time.  They worked.
And they didn't need to take the 68000 apart to the silicon.  Just
attached to its pins and took over from there.

Couldn't the same thing be done with Clipper?
A pin compatible, bus-protocol compatible, but communications
incompatible chip attached to a switch that lets you select between the clipper and the replacement?