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How to define an internal clock in DC?

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liwei039

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clock mux

I just want to define an internal clock in DC. this clock is come from a mux of two input clock then through a combination logic.

should be use create_generate_clock? how to use it?
 

aravind

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yep use create_generated_clock command
 

hfooo1

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the two clocks work coinstantaneously or not?

in either situation i dont think it's needed to define a clock.
 

dcreddy1980

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As you said, the clock is an output of mux, basically i would use a case analysis on the select signal and select which ever clock u want for the optimization, its a better scenarion in your case.

if you have two clocks lets say clk_a and clk_b as inputs to mux, clk_a is connected to select(0) pin of mux and clk-b is connected to select(1) of mux, if you want to optimize the block with worst scenarion where u feel the block can be made robust, then select a high speed clock.

set_case_analysis 0 [get_ports select]
// assumed mux select to be input or define the hierarichal path and now ith above command, it will select clk_a for the analysis
 

dechen

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sometimes you may want to define a new clock at the mux output, so a new clock tree can start from the new clock. For synthesis it does not a difference, but it maybe useful for clock tree synthesis.
 

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