multicyle path across clock domain

[harpv]

I understand that a set_multicycle_path can be specified between two different clock domains.

If the source and destination clocks are synchronous I believe there isn't much confusion.

But if the clock domains are asynchronous, how does the STA tool handle it? I haven't seen this getting used in my experience yet, just curious about it. :?:

Assuming no asynchronous clock group or false path setting.

 

[hoanglongroyal]

why do you care about asynchronous paths?
in STA, you have to specify asynchronous domains as they're (set_clock_group async), and the tool will consider them as false paths together. if you do not specify, then STA tool consider them like sync domains and check timing between them by searching common edge timing.
just need make sure you implement synchronizers between domains.

 

[sharath666]

Hi harpv. From where did you get the info that this command can be used between 2 different clock domains? I just checked DC documentation. I got no indication that this is true..

 

[harpv]

sharath666,

I believe its not explicitly stated. But my understanding is you can specify -from and -to endpoints which belong to different clock domains. One case I can think of is when the destination is a divided clock of the source clock.

So the command in itself doesn't place any restriction. Only that it doesn't make sense to put async clocks as from and to.

 

[sharath666]

Yes..It doesn't make sense. You might as well declare them as false paths..