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WireLoad Models At Each Stage in Physical Design Flow

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Jul 25, 2005
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wire load model

During the PD flow(magma), different wire load models are associated at different stages like Constant, Manhattan, Final. Can you let me know which Wire Load Model is associated at each stage.
WireLoadModel Stage


physical design stage

hi hb_cancer,
I never used magma flow, but i am wrking on other tools from quite a long time, wht i don't understand is why we do require wireload models at diff stage,, we generally use in synthesis,, and wont later,, can u more elaborate ur question

timing report wireload model

Hi raju3295,
I had this query because when I look in to the timing reports at different stages of the design like Timing Optimization(FixTime), Cell Placement(FixCell) or routing(FixWire) the "wire load model" in these reports are different, even though we don't explicitly specify which model to choose for the tool. Can you let me know what has to be the appropriate wire load model for different stages of the flow(backend)... Thanks...

extract rc wireload model

Hi Hb_cancer/Raju,

Yes, PD tools uses different wire load models at different stages. Because in the implementation stages as we can not use sign-off tools for extraction because of runtime(Or we may not require that accuracy) and also we will not have complete routing information. So physical design tools uses different wire load models to model parasitics.

Then why is different wireload models at different stages?
As we proceed with flow even we need to have accurate wire model as close as possible to sign-off tool so that we would t not see any surprise results when do STA with sign-off tools(StarRC-xt Industry sign-off parasitics extract tool, PrimeTime/PrimeTimeSI Industry sign-off STA tool).

Then come to hb_cancer question,

WireLoadModel Stage
1. CONSTANT or Zero wire load Model used during fix-time stage
2. Global wire load model used during fix-cell/fix-wire stage (Because first global routing is done at fix-cell stage and again during fix-wire stage)
3. MANHATTAN -During CTS/Partial at Fix-wire stage (I am not sure)
4. FINAL when detail routing is done i.e at the end of Fix-wire Stage.

I hope this helps.


physical design + fixcell

hi hb_cancer/arjun
Generally cdn/snps tools will do rough virual/trial routing for estimating the distance and thus will calculate the RC values and sure this is not a signoff one, but to have some estimation,, these tools will do this rough routing& estimation.
I used to have a strong feeling About wire load models , is they will be used where the design is not placed and from these tables depending upon the size of chip and fanout,, tools will cal RC values.... Correct me if am going wrong some where

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