3 Replies Latest reply on May 30, 2008 10:19 AM by guan

    How do you merge your P&R design and GDS IP cells together



      When designing in P&R environments, standard cells and IP blocks are represented as LEF cells with abstract data in them. To run Calibre DRC or LVS on a GDS file, the DEF design must be translated to GDS and all of the LEF cells must be replaced with their GDS equivalent that contains the mask level data to be verified. I can think of a few ways to do this.





      1. Specify multiple files in the LAYOUT PATH statement of the SVRF rules file

      2. Use Calibre DESIGNrev *layout merge *API command

      3. Use the new Calibre DESIGNrev layout filemerge disk-based merge

      4. Merge within the P&R tool or *other *method.


      I think each of these may have some advantages and disadvantages. How do you do this and why?





        • 1. Re: How do you merge your P&R design and GDS IP cells together

          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:-


          HCELL file:


          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.

          • 2. Re: How do you merge your P&R design and GDS IP cells together


            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. 



            • 3. Re: How do you merge your P&R design and GDS IP cells together


              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.



              Our approach:



              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.