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Do we need to read the sdf to do STA after P&R ?

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xworld2008

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spef rc corner sta

Afer P&R , we can get a netlist and sdf file. We should redo sta analyse, Do we need read the sdf to do the STA?
 

primetime read_sdf pdf

Of course. SDF from backend tools include accurate timing delay information.
 

simulation backannote

Hi xworld2008,

Post P&R STA is to check that the layout implementation meet the timing requirement. The interconnect RC after P&R is different from the estimate before layout.

For sign-off, typically you have to use "sign-off quality" tool. The engines (timer, rc-extraction, noise etc) in a P&R tool is typically not good enough for sign-off. So use tool like star-rc or XRC to extract the RC of interconnect to a spef format. Read the spef into STA tool (e.g. PrimeTime). The STA tool can do the delay calculation and perform STA. At the same time, the STA tool can write out a SDF file for post-layout logic simulation.


Regards,
Eng Han
 

Re: STA after p&R,

Yes you must use SDF + SPEF to backannotate the layout+routed timings. Once you have these values the WLM is now based not on estimation but more on both physical placement and the actual RC + lumped capacitance values.

Now with new values you can run STA again to verify the timings are met.

Otherwise backannotation has no meaning.
 

STA after p&R,

i use Astro to P&R。Can the sdf extracted from Astro be directly annnotated to the simulation tool for post-layout logic simulation?
 

Re: STA after p&R,

YES,

But it is strongly not recommanded.

Please use STA instead of simulation. And also extract parasitic paraters by exporting RSPF, DSPF or SPEF file from Astro and do a post-layout STA.
 

Re: STA after p&R,

eda_ak said:
Yes you must use SDF + SPEF to backannotate the layout+routed timings. Once you have these values the WLM is now based not on estimation but more on both physical placement and the actual RC + lumped capacitance values.

Now with new values you can run STA again to verify the timings are met.

Otherwise backannotation has no meaning.


is it right if I used only SDF to backannote the post_layout netlist in STA?

why need SPEF?

whether those files such as spef are must?
 

Re: STA after p&R,

To perform STA after P&R with SDF file, do we need to specify the type of SDF we are going to use in the primetime...There will lot of corner cases like Temparature of 110C and voltage of 1.15 volts. consider that i am not going to perform cross talk analysis for my design.

Ex : read_sdf ./test.sdf
 

Re: STA after p&R,

Why read spef?

Here is the answer:
For timing critical nets (such as clocks and others in your design) .spf is most accurate. For others you can survive with pdf. But DC doesn't understand .spf!!! So normally you need .spef after Detailed routing not after Global routing.

So here is what you do:
First get only sdf + net_capacitance (set_load format).

After almost all timings are fixed then get spef into PT.

...still learning
 

Re: STA after p&R,

Could somebody upload/or specify a good book which describes STA in detail.
Thanks,
Ajith.
 

STA after p&R,

Hi ajitr99,

You can find the e-book named <Advance ASIC Chip Synthesis> in this forum.
 

Re: STA after p&R,

read sdf file, then
analyze setup time in slow corner.
analyze hold time in slow and fast corner.
analyze noise impact.
clean setup and hold time.
 

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