the difference between ungroup and set_flatten commands

[owen_li]

set_flatten

What is the difference between ungroup and set_flatten commands in Design Compiler? It seems that they are both used to flat the design. Help me!

 

[usaid]

design compiler ungroup

the ungroup command removes the hierarchy in the design (netlist) and make it flat..
you can use set_flatten command (options are true and false) to enable and disable this behavior during logic optimization (during compile)...
By default it is set to be false...

 

[sam536]

ungrouping a module design compiler

Ungrouping will remove the levels of hierarchy in a design , where as flatening (Set flatten) is optimization technique for reducing the logic levels and improving the speed of the design.

Flatening works by converting the combo logic into two level SOP(sum-of-product) form and removing intermediate terms. where as by ungrouping the design , by which removing the hierarchy and combining two logic blocks,It will produce more optimization solution.

Flatening is controlled by User. Default its off. Depends on the arithemetic logic used in your design, you can enable set flatten command. Flatening is expensive solution.

How set_flatten Worsk in DC :
Product = X * W;
X = Y+Z;
when you set , set_flatten true in DC , the optimization will be ,
product = (Y+Z) * W => Y*W + Z * W;




Flattening optimization technique used only in the regular compile , not in the incremental compile.

 

[shiv_emf]

difference between ungroup and flatten in dc

set_flatten ---> u shud be knwing compilation process....
in logic optimization... there r two types of optimization
1) structural(default)
2) flattening

by default, structural optimization takes place..... to enable flattening ---(plz note tht.. flattening doesnt mean removing hierarchy... in some circumstance v mean tht..)

ungroup is to remove hierarchy !!
regards
Shiv