Document the difference between "DFFRAM Compiler" and "DFFRAM/OpenLane"

[xobs]

The README lists DFFRAM densities for both "DFFRAM Compiler" and "DFFRAM/OpenLane". Please elaborate on what this means, since "DFFRAM Compiler" appears to be 2-3x better than "DFFRAM/OpenLane".

My reading is that if you use the output from DFFRAM in a commercial compiler tool, you can improve it by 3x versus using OpenLane, but I'm not sure if that's what it means.

[antonblanchard]

My understanding:

• DFFRAM Compiler uses the entire DFFRAM flow where it places all instances
• DFFRAM/Openlane uses the DFFRAM verilog, but relies on OpenLane (well OpenROAD) to do placement.

It's not a comparison to commercial tools.