( ESNUG 364 Item 2 ) --------------------------------------------- [02/01/01]
Subject: ( ESNUG 363 #2 ) Watch Out! Presto Tied Gate Outputs To Ground!
> Presto makes me nervous. Changing the way MUXes and arrays are translated
> to gtech sounds like two different circuits to me. Infer enumerated types
> should be defaulted to off to be compatible with earlier releases.
>
> - Dennis Milton
> Stratus Computer Marlboro, MA
From: Scott Evans <scott@sonicsinc.com>
Hi, John,
I had tried using the Presto option with the 2000.05 release and ran into at
least one bug was reported as a timing loop. This resulted in STAR 113486.
These loops did not exist when Presto was not used. At that point, I dumped
out a netlist to see what DC was talking about.
GTECH_OR2 C1723 ( .A(N2188), .B(N2189), .Z(1'b0) );
GTECH_AND2 C1724 ( .A(1'b0), .B(N2187), .Z(N2188) );
When I looked at the gates I noticed that it assigned the output of an OR
gate tied to 1'b0 !!! (I'm sure the physical layout software would love to
route ground to the output of a gate.) Furthermore, DC seemed to be
treating this constant as a real signal so when the constant was used
as an input to the gate which originally generated the 1'b0, DC thought
this was a loop. So, I would suggest that you carefully examine the
error/warning/informational messages you get in DC if you try Presto
in 2000.05.
- Scott Evans
Sonics, Inc. Mountain View, CA
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