Why is SDC required for PTPX?

[ishbis]

Hi
I am running PTPX for time based power estimation using VCD for switching information.
I wanted to know that since all the switching information for nets/clock etc are present in the VCD why do we require the SDC for VCD based PTPX flow?

Kindly answer this query

Thanks

 

[rca]

SDC provides the clock definition, then you do not need to define the clock starting point(s) in the primetime px.

 

[ishbis]

Hi
Thanks for your reply.
As per my understanding the clock definition would be there in the VCD as well (along with the switching info for the clock).
So any information provided by the SDC would get overwritten with the info in VCD.
So why would we require the SDC?
Could you kindly ponder on these lines and repond?

Thanks

 

[rca]

the VCD contains only toggling net informations, that include the clock nets, but the SDC will indicate the clock source, and the tool could trace the clock nets, and find the activities of this net in the VCD file, and then estimate the power consumption only for the clock tree, for example.
is it more clear?

 

[ishbis]

Hey
If my understanding is correct, the toggling for the propagated clock nets would be there in the VCD as well right? So irrespective of the source the toggling info. for every clock net would be available for power estimation
Kindly clarify this

 

[rca]

yes the VCD contains the toggle for the clock nets, but PrimeTimePX does not know this nets is associated to the clock, and does not the source and where you cut the clock tree.

 

[dftrtl]

You need SDC only if you want PT-PX to report clock network power separate other wise there is no difference in total power and you do not need SDC