( ESNUG 387 Item 3 ) --------------------------------------------- [01/23/02]
Subject: ( ESNUG 386 #1 ) This PhysOpt Bug Only Involves Buffers/Inverters
> One of the ACs in San Diego told me about a situation where PhysOpt can
> put "extra inversions" in your netlist and create bad logic. This
> problem can occur if your library has certain cell that can act as *both*
> a buffer and an inverter.
>
> - Mike Montana
> Synopsys, Inc. Dallas, TX
From: "Chris Kiegle" <ckiegle@us.ibm.com>
To: "Mike Montana" <montana@synopsys.com>
Hi Mike,
I saw your ESNUG 386 #1 post and I wanted to check on something....
You said it is only a problem if the pins are in a different order. All
libraries have to have an inverter. If they also have a buffer cell, there
is always going to be mismatch on order between the multi-output cell and
one of the two (inverter or buffer), right? Does this problem also impact
sequential elements?? In other words, if I have 3 D flip flop cells, one
that has D output, one that is an ~D output, and one that has both outputs,
will it also hit this problem??
I'm just wondering if there is any relation to the library functional
descriptions.
- Chris Kiegle
IBM Microelectronics Burlington, VT
---- ---- ---- ---- ---- ---- ----
From: "Mike Montana" <montana@synopsys.com>
To: "Chris Kiegle" <ckiegle@us.ibm.com>
Hello Chris,
Here are some more details regarding the bug documented in ESNUG 386 #1.
First of all, let me assure you that the bug does NOT impact optimization
of sequential cells or combinational cells. The problem is strictly
limited to optimization of buffers/inverters.
I've spoken with the product team to get more specifics of when this
problem occurs. The problem ONLY occurs when the PhysOpt optimization
engine tries to replace a simple buffer (one input and one non-inverted
output) or simple inverter (one input and one inverted output) with a
complex buffer (one input with a non-inverted and inverted output). All
other types of optimizations with these cells work fine.
Keep in mind that this bug will be fixed in a PhysOpt patch release
scheduled for EST availability the first part of February 2002.
- Mike Montana
Synopsys, Inc. Dallas, TX
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