( ESNUG 276 Item 4 ) ----------------------------------------------- [1/7/97]
Subject: (ESNUG 274 #8) What's Better? "Rich" Or "Sparce" Synopsys Libs?
> I have been involved in an effort of generating Synopsys libraries.
>
> The target is to be able to compile a design to the fastest speed. One of
> the questions that arises is how "rich" the library should be? Some
> libraries out there have over 1000 cells, but, on the other hand, some have
> much fewer cell selection (~300). I know, theoretically, more is better,
> but I have seen cases where it does not apply. For example, we had a
> complex gate that had (by mistake) only one size. Removing the cell made
> the design synthesize to a faster speed. It seems like Design Compiler
> picked up this cell, assuming it could bump up the size, but then when it
> found out it cannot do that, it could not recover.
>
> Does any one has any experiece with this? Is there a DC runtime penalty
> for using the rich libraries vs sparce libraries?
>
> - Erez Naory
> National Semiconductor Hertzlia, Israel
From: abair@parsons.sps.mot.com (Alan Bair)
Hi John,
From what I have read and heard in talking to other users within Motorola
and Synopsys support, there are a couple issues.
* For each function in the library, there should be 4-5 sizes to
provide for adequate choice in sizing.
* Performance is not hurt until the library has several thousand cells.
* Once all the basic functions are handled the best way to improve a
library seems to be to look for common pairings Synopsys is making
and turn those into extra cells.
Hope this helps.
- Alan Bair
Motorola
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