( ESNUG 250 Item 6 ) -------------------------------------------- [9/6/96]
From: Ross Swanson <swanson@est07.bwi.wec.com>
Subject: I *Always* Want "Selecting Critical Implementations"
John,
If I synthesize a 20 bit adder I get around 30ns performance, but if I
use set_max_delay and compile, the timing is reduced to just over 7ns.
This option enabled 'Beginning Resource Allocation' to use 'Selecting
critical implementations', and so a Carry-Look-Ahead adder was picked
from DW01, instead of a ripple adder.
Why didn't I get the fastest adder from DW01 without set_max_delay?
And what if the adder is buried around other logic, how do I use
set_max_delay so that I don't get a ripple adder but Carry-Look_ahead?
Or is there some secret Synopsys switch known only to the High Priests
of Synopsys that will always enable 'Selecting critical implementation'?
- Ross Swanson
NorthropGrumman
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