why we do hold analysis after cts?

[jitendravlsi]

hold check after cts

hi ALL,

Plz tell me

why we do hold analysis after cts?
why we cant do before cts?

 

[koggestone]

Re: hold check after cts

Hold time problems are easier to solve compared to Setup time problems.

Hence Goal is to solve setup time problems first during synthesis.
and worry about hold time problems later (after CTS).

 

[jitendravlsi]

Re: hold check after cts

dear,

if this is the case then we could do first setup analysis and then hold analysis before cts itself, but this is not possible to do both before cts.

urs may be one of the reason,

but there would be some more specific reason behind this logic..

any body else?

by the way thanks for quick reply..

 

[flyinmeteor]

you want to get an accurate timing before you start hold analysis...
for my experience we usually wait until we have fixed all setup problem...

 

[ljxpjpjljx]

because after you do cts you will have some hold time issue!

 

[jitendravlsi]

hi dear

thanks for reply.

but still i am not satisfied with answers..

 

[dcreddy1980]

one of the reason is due to clock tree and clock skew which play crucial factor for hold timing analysis. You can have real clock tree and clock skew only after place and route. I hope you understood what i am trying to say. If not let me know, we can discuss further

Regards,
dcreddy

 

[jitendravlsi]

Dear Reddy,

Thanks for reply...

though you tried to give some proper reason, but still I am not fully satisfied with the answer.

please explain in more detail...

1) what will happen if we do hold analysis before cts?
2) how the hold analysis will be different before and after cts?

please help me to understand this concept.

thanks
Jitendra

 

[arjun1110]

Hi Jitendra,

Clock will be propagated only after CTS, till then it will be in Ideal mode i.e delay in the clock path will not be calculated which is optimistic for hold analysis. That is why hold violations will be checked after CTS.

Hope I answer your doubt.

Regards.