( ESNUG 256 Item 5 ) -------------------------------------------- [11/22/96]
From: ajayn@sol-tx.sps.mot.com (Ajay Nath)
Subject: How Do I Constrain My Funky "Ordered-Input" Combinational Cell?
Hi John,
Here is a query for the Synopsys gurus out there.
I have a *combinational* library cell with multiple inputs is designed in
such a way that it is critical for the inputs to maintain an ordered
relationship with one another. Is it possible to model such a constraint
into the library cell, such that Synopsys will enforce this order?
Consider a cell with function f(a,b,c). Due to circuit design issues,
the function requires that input "a" be set up prior to input "b." In
other words, input a has a setup requirement with respect to input "b"
for the function to be correct.
The library attribute "timing_type" does not have any setup/hold values
for *combinational* circuits. Does anyone have any ideas on how to force
synthesis to design in this relationship? If this cannot added to the
library cell description, is there a generic approach to solving this
problem using DC commands?
- Ajay Nath
Motorola
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