Re: MISC-d Digest V97 #7

[jfox@xxxxxxxx (Jeff Fox)]

Dear MISC readers:

Sorry I missed one of the questions...

>From: houghtoa@oclc.org (Houghton,Andrew)

>Has Chuck given any thought to providing a RAMBUS interface to memory
>on his chips?

Yes he has considered this and other memory options.  He has been pretty
conservative in his concern about which memories will be avialable and
at what price when the chips he designs will be in production.  He had
some concern about designing for designs that get hype if he is not
convinced that they will actually be available and cheap when a cpu
design is finished.  These things are hard to predict.

He has been preparing about one or two chips for fab each month in
his efforts to get his OKAD environment really in sync with the fab
process so that when his simulator says a chip will work that it
really will.  The problems have tended to get smaller on each design
but there are still some problems.

There will be some of this again as Chuck moves to new processes with
new manufactures but once i21 and F21 a finished he will be able to
experiment with many new design choices and certainly the kind of
memory chips is one of the things he can pretty easily change.

The biggest change will be on chip memory since it gives the biggest
gain in speed, but there are also many ways to improve memory bandwidth.
Remember Chuck's first chip at NOVIX more than ten years ago used three
busses and three memory spaces to do nice stuff.  That one reason it
could do several things in a single clock cycle.  MISC chips could
also have bigger or multiple memory busses.

One consideration so far has been development costs.  P21 needed 8 fab
runs.  Between F21 and i21 there have been lots of fab runs to get
the chips working.  Adding a single pin to one of these designs would
have doubled prototype fab cost and it is not like there has been extra
hundreds of thousands of dollars available for this development.  P21
and F21 development were just paid for out of pocket and iTV has
struggled for financing durring much of its history.  As iTV ramps
up we will be making chips with on chip memory and new memory busses.

    Jeff Fox
    jfox@dnai.com              Ultra Technology Inc.
    jeff@itvcorp.com           the iTV Corporation
    http://www.dnai.com/~jfox/