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From: Laurent Claudel <laurent.claudel@massana.com>
Subject: Help! DC's Wrecking My Scan Chains In Incremenatial Compiles!
Hi John,
I have a netlist with a scan chain inserted. Now I want to do an
incremental compile on that netlist without the Test Compiler. I've tried
to put a set_dont_touch on every register and every scan chain net (the one
which are connected to the DB input of my scannable register).
Unfortunately, this doesn't stop Design Compiler from messing around with my
scan chain since the set_dont_touch on a net applies only on combinatorial
cells connected to that net.
What happens basically is that Design Compiler is re-routing my scan chain
thru inverters to try to reduce the fanout on other critical paths. So
instead of going from Q to DB, it goes from QN to DB thru an inverter. Not
really what I want for a scan chain !!!
This scan chain wasn't generated by the Test Compiler at the first place.
If anyone has a suggestion, that would be great.
- Laurent Claudel
Massana Ltd Dublin, Ireland
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