When we need a mixture of LEF-DEF data for the design and GDS data for selected standard cells or MACROS, Calibre xRC allows for selected LEF cells to be swapped out in favor of GDS views at extraction time for more accurate extraction of over the cell (OTC) routing.
This flow is designed for situations where large macros, e.g. RAMS or analog blocks have routing above them and the LEF abstract model does not represent the geometries inside the cell as ‘seen' by the routing above the cell. In this case the GDS can be inserted into the design for extraction so the contents of the cell as seen by the OTC routing are more detailed and accurate. This situation can occur if the LEF model for the cell is for example a simple single plate abstract for routing.
The requirement here is that BOTH the LEF and the GDS descriptions for the cell are available and are read in during extraction. The LEF abstract model for such a cell will be in the existing LEF files, The GDS model of the selected cell will be provided via the HCELL file in the form:-
MY_RAM -gds layout/MY_RAM.gds
Here the cell to be swapped is called MY_RAM in both the LEF-DEF and GDS views, the location of the RAM GDS file is layout/MY_RAM.gds. The GDS view must have the same name and number of I/O pins as the LEF model for the RAM, for the views to be synchronized.
That's interesting. I don't think this will apply to DRC or LVS users, but it is of value in the extraction space. I'm really trying to understand how DRC and LVS users merge their data together prior to launching a DRC or LVS job. Calibre can read open industry standard databases like OpenAccess, Milkyway, LEF/DEF, and Oasis but GDS is still the most widely supported format. That being the case, checking the database format that will be shipped for manufacture is a good choice as you near tape-out.
I'd like to know what methods are being used and why.
We use Mentor ICStudio to perform the final chip level assembly and other layout edits, and we use P&R tool from a 3rd-party vendor.
1) Generate a GDS file from the P&R tool;
2) Import the GDS file into ICStudio using iclink. Here we specify what the references libraries are for the Standard cells and IP macros.
3) Then Run DRC, LVS, PEX using our default flow: output GDS from ICStudio, and run Calibre.
My latest pet project has been to use DEF, to replace GDS, as the go-between. It has not been easy though, as vendors seem to understand DEF/LEF differently.