Re: While doing Synthesis who gives us the constraints to se
For module/block,constraints comes from the top-level requirments.
For top-level it self, constraints comes from the spec or from the customer requirements.
If your top-level design is hierarchy(i.e design having more than one block) and you have only top-level constraints, there are tools like synopsys dc_shell which will derive constrains for individual modules/blocks.
I have attached synopsys document on design budgetting. Hope it will helps.
Regards,