> I remember a few years ago we would have to run ISE PAR several times
> in order to meet timing. One we had a decent layout, we would lock
it
> down because of the chance of never being able to reproduce it.
Howdy Tom,
> Does ISE still suffer nondeterministic placement?
I wouldn't call it nondeterministic. To me, non-deterministic means
that if you give a single version the EXACT same input two times in a
row, you might get a different output. I don't believe that has been
the case for a while now.
What DOES happen is that if you change even the slightest thing, the
synthesis tools (and therefore MAP and PAR) can take a VERY different
"path" to implementing, mapping, and placing the design. Each is
dependant on the previous step - so I think of it like the butterfly
effect - a small (almost insignificant) change at the input can make
huge changes at the output.
That behavior most definitely does still exist - but the only suffering
going on is on the part of you and I :-)
> Also, how much has ISE PAR improved since 5.1/6.1?
I'll take a stab since noone else has. The last huge improvement that
I noticed was the -timing option for MAP, which I thought was
introduced (or at least revamped) in 6.x.
Other than that, I'm sure their algorithms have improved in general,
but I've heard WAY too many cases, both on c.a.f and outside, of people
re-running with newer versions tools and getting considerably different
results (either it not fitting, or timing being off by a mile, or new
errors, or in our case, the default I/O bank type changed). Even on
dot releases, like between 6.1 and 6.3.
Lastly, higher speed and/or density designs in the older families
(Virtex, Virtex-E, Spartan-II and Spartan-IIE), 6.3 is probably what
you want:
http://www.xilinx.com/xlnx/xil_ans_display.jsp?getPagePath=21382
Marc
Reply by Tom●May 23, 20052005-05-23
I remember a few years ago we would have to run ISE PAR several times
in order to meet timing. One we had a decent layout, we would lock it
down because of the chance of never being able to reproduce it.
Does ISE still suffer nondeterministic placement?
Also, how much has ISE PAR improved since 5.1/6.1?
-Tom