set_clock_uncertainty in a design

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raviram80

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Hi All,

After the CTS is done the clock skew is gone out of uncertainty. when we do set_clock_uncertainty in primetime what is left is Jitter number,

Can you tell me what other things besides the Jitter could be contributing to Uncertainty?

I am talking of both uncertainty for hold and setup calculations.

Thanks a lot.
 

Hi, there is always clock skew after CTS.

CTS builds a clock tree that will have (hopefully) minimal skew or uncertainty, hopefully it has skew lower than what you told the synthesis tool, otherwise you will probably get timing violations

When you do STA and set clocks as propagated, the tool figures out all of the different arrival times from the source of the clock to the destination CK flop pins. the tools uses these arrival times to check for setup/hold slacks.
 

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