PDP era and a question

From: Cassic Comp Reader <class_at_fliptronics.com>
Date: Sat Aug 28 21:08:44 1999

While the thread has wandered far from the subject line, I am compelled
to respond to some of this.

Please Tony, this is not an attack on you. There is a lot of
about FPGAs IP, software, and architecture. This thread has just
my "sit back and read" threshold.

Tony Duell wrote:
> Anyway, the real point is that certainly for Xilinx FPGAs, if you buy the
> official tools you get a program to 'reverse engineer' a bitstream back
> to the CLB map. Converting that to a schematic is still a non-trivial task...

This is ABSOLUTELY NOT TRUE. There is NO tool that can reverse engineer
the bitstream to anything. Neither internal to Xilinx or external (and
announced). There is ONE instance where the bitstream was "forward"
engineered to find the mapping between design primitives and the
bitstream, and this was done by a company called Neocad, and they were
acquired by Xilinx. The process they used did not have the capability of
taking an existing design bitstream, and decoding this into any type of
design database. The final translation from design database (NCD in
tools, LCA in prior generation) to bitstream is unidirectional. If you
to make changes to your design, you make them to the design database. If
you desperately want to make design changes to the bitstream, Xilinx
provides as part of the standard tool chain, LL files that point you to
but not all bits in the bitstream (LUT bits, and some FF bits. NO
bits). Xilinx also provides a tool called JBITS, which can also modify
the bitstream, and might be used to create a reverse engineering tool,
this has not been done to my knowledge. With regard to the "and
above, it is possible that an organization like the NSA may have done
something like this, but they haven't told me about it.

Even if such reverse engineering tool existed, you would end up with a
CLB map, which I agree would be non-trivial to get into a useful

> Not just me, I know of research groups who are having problems with this
> due to the loss of the XC6200s...

While the research groups that weren't distracted by XC6200, and
with the XC4000 and its descendants, have not wasted time screwing
with tools, and have gone on to do some real useful stuff. See the
proceedings of the annual IEEE FCCM conferences.

> And yes, I've tried. The policy is that this information will not be
> available, except possibly under an NDA (which would have been no use to
> me).

Flip-flop and LUT position in bitstream for an existing design:
                        Directly avail in LL file.

FF and LUT position for all bitstreams (alg for calculating it you self)
                        Avail under NDA.

Mode control, some more I/O info, but not routing info:
                        Avail under a tougher NDA.

The whole lot:
                        Avail under a very tough NDA.

> > > Most (all?) of the existing work on such systems was done using the
> > > now-discontinued Xilinx XC6200 series. Those were fully documented (I
> > > have the data sheets).

This product has not been discontinued. At last report, Xilinx said that
parts would continue to be available to anyone that wanted to buy them.
Further development of the family has stopped. Further development of
support software has stopped, but that is not an issue, because you plan
write your own.

see: http://www.vcc.com/RPU.html#anchor581456 status
        http://www.vcc.com/Papers/6200.pdf data sheet

> > This implies there wasn't a good reason to continue supplying the
> > documentation to the public. Too many idiots trying to write their
> > own tools and calling tech support hourly when it didn't work?

Unknown. Data sheet is still available from


and from Xilinx by request.

> The official reason why the XC6200 was dropped was because they didn't
> sell enough of them. This could have been due to the fact that no
> distributor that I 'phoned had ever heard of them. It could have been due
> to the fact that they were so differnt from other Xilinx parts that they
> didn't really do the same job, and people didn't realise what they'd be
> useful for. Or maybe the real reason for dropping them is totally
> different anyway.
> -tony

Or maybe, they didn't sell enough. If the only people buying a chip is
university researchers, in 1-10 piece quantities, it is not a viable
Received on Sat Aug 28 1999 - 21:08:44 BST

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