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Subject: custom wireload model from first encounter
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ccl123
Posts: 0
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2/17/2005 10:03 PM  
hi

Does anyone use this wireload model to synthesis in synopsys ?

i have huge interconnect delay after using this cwlm .

Is this normal ?

thanks
crispy_duck
Posts: 0
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2/06/2006 7:14 AM  
Hi,

We don't use custom wireload models. Our synth is run using the smallest "realistic" model in the library (auto selection is disabled), and is purely use to allow us to have some load on nets when running optimisation. Our real aim is to get a netlist into layout as quickly as possible, and utilise post-placement optimisation to achieve better timing results.

The only thing we try to push for in synth is the fastest architecture for things like adders etc. However we do try to ensure that the resultant netlist doesn't utilise many high drive-strength cells (instead reserving them for the layout opt phase).

Whether using custom or library wireloads, you run into issues when timing between blocks or at the toplevel. Yet in placement, the decisions made by the synth tool can be completely wrong.

Of course, someone will now come along and give an alternative view.......

CD
evenditti
Moderator
Posts: 23
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2/06/2006 12:14 PM  
Hi,

I don't usually use custom WLM but if you do you need to make sure that first you have a good parasitic correlation i.e. your cap tables and scaling factors are set so that an encounter extracted spef will match (within a resonable error margin) your signoff extraction tool. If not you will have serious problems.

In general using a small wireload models from your library should be good enough for synthesis assuming that you will provide realistic timign constraints (and use them) to your placement/routing tool.

Hope this help,
Eric.

Eric Venditti
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Forums > Digital IC > Synthesis and test > custom wireload model from first encounter


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