[oc] Top-Down Vs Bottom-Up

["R. Ramakrishna" <rayaprolu_rk@yahoo.com>]

Hi All,

 

My question may seem very trivial, but it is pretty tricky in my opinion.  I request to be corrected where ever I go wrong.

 

Question is:  In Basic Digital design, how do we distinguish Top-Down approach and bottom-up approach?  Will there be any difference in the RTL source files I obtain following these apporaches?  If no, then how do we define them, apart from the text-book definition, which says, "In Top-down approach, the algorithmic level of the problem is first stated, then the problem is modularized, so as to use a divide-and-design approach till a possible lowest level is obtained." and "In Bottom-up approach, the existing lowest level module is used in building a superior task and that is further used in building a more superior task and so on". 

I could define the two terms at the synthesis level (using DC terminology, of-course) as follows: 

Top-Down compile would mean I would read-in the whole of my design to the memory, apply my optimization constraints at the top-level only and then compile.  In case of a re-compilation, I would still have the top-module as my reference and apply attributes and constraints to my sub-designs using hierarchical definitions.

Bottom-Up compile would mean I would read-in one sub-module at a time, with my sub-design-specific constraint files, compile each of them independantly, finally read-in my top-module, then link and compile with top-level constraints. 

Thanks and Regards,

R. Ramakrishna

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