( ESNUG 242 Item 5 ) ---------------------------------------------- [7/11/96]
Subject: ( ESNUG 240 #4 ) Backannotation, Visibility, & 'Characterize'
From: rray@msai.mea.com (Russell Ray)
> I'm not an expert on what is really happening but I ran into this same
> problem with only using set_load and set_resistance commands. It appears
> that the loads are only visible if the current design is set to the same
> design as whey you performed the set_load commands. When the current
> design is anything else, they are not taken into account.
From: rnair@BayNetworks.COM (Rajesh Nair)
> Design Constraints, Timing constraints and any Backannotated parameters will
> only apply in the context of the design to which it was applied. (Because
> one could potentially be using the same subdesign in other designs or in
> another context in the same design. In this case, you would not want the
> backannotated value from the previous design to be present any more.)
From: greg@cqt.com (Greg Bell)
John,
I don't think this is true... there's another case. What they're talking
about is executing the set_load commands from the top level, and their effect
not being visible when you make the current_design a lower level (moving
DOWN the hierarchy).
But we're backannotating lower blocks, then moving UP the hierarchy. Just
now I ran a test, doing a "diff" of two "report_constraints -all_violators".
One report was generated after backannotating my way, and the other by
backannotating from the top level (after editing the backannotation files to
have the correct hierarchy information). The reports were the same.
So the generalization that the set_load commands are only visible from the
design where they were run seems incorrect. Rather, the tool will propagate
their effects up the hierarchy, but not down it (use characterize for that).
- Greg Bell
CommQuest Technologies
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