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LEF in synthesis flow

diablo

Hi,

In RTL compiler synthesis flow, i have

set_attribute interconnect_mode ple /

And, i have inlcuded the cap table as well

set_attribute cap_table_file {$CAP_TABLE/bst.cap } 

Do i need to include the LEF library for std cells and io cells as well for correct interconnect delay estimation even after including cap table?

It seems including LEF file gives significant difference in total number of cells and area after synthesis as reported from RTL compiler. Below is the snippet of area report for two flow, 

one excluding LEF

 Cells       Cell Area       Net Area

 23283       715947       391632

and the other including LEF file 

Cells       Cell Area       Net Area

 22664       967042       246572

 Which one is correct flow? Or, which one is the better flow?

Thanks for your suggestions and your time.

Regards. 

Parents

  •  Hi diablo,

     likely case is you are missing some LEF models for your memories. By default RC will zero macros that do not have corresponding LEF info. Indeed you always need your LEF models for cells, process, etc. The reason is the capTbl does not include any of that information. capTbl strictly has process information so it is more detailed in that respect but still missing plenty of information. As per recommended flow, you should certainly read in all LEFs as well as the capTbl. Setting the mode to PLE is not required since reading any LEF or capTbl will make RC default to PLE which is indeed the recommended mode. Here are some articles from http://support.cadence.com that may be of interest to you

     

    87%
    How is cell area picked in RC-PLE flow?

     

    During optimization with PLE mode does RC use the lib area or lef area? Also is there a way to force RC to use the LEF area? Using the LEF area is supported in 7.1 and is default in this version.
    Show Attributes

    10-27-2009
    84%
    RC PLE: Cell area for macros is shown as zero. Why?

     

    Shouldn't the area be taken from .lib in absence of LEF information? As per the current behavior, if physical information or LEF for some macros are missing then their area will be shown as 0. The area of 0 is expected when LEF for the corresponding macros have not been read in.
    Show Attributes

    10-01-2008
    73%
    What can go wrong if the cell areas in Liberty library are different from LEF?

     

    Problem: What can go wrong if the cell areas in Liberty library are different from LEF? Solution: RC uses the area numbers from the LEF files when the LEF files have been read in.
    Show Attributes

    07-07-2010
    70%
    Does RC use cell areas from LEF or from Liberty in PLE mode?

     

    Problem: Does RC use cell areas from LEF or from Liberty in PLE mode? Solution: The cell dimensions defined in the LEF will be used if the LEFs have been imported and the tool is in PLE mode.
    Show Attributes

    02-02-2009

     

    regards,

    gh-

Reply

  •  Hi diablo,

     likely case is you are missing some LEF models for your memories. By default RC will zero macros that do not have corresponding LEF info. Indeed you always need your LEF models for cells, process, etc. The reason is the capTbl does not include any of that information. capTbl strictly has process information so it is more detailed in that respect but still missing plenty of information. As per recommended flow, you should certainly read in all LEFs as well as the capTbl. Setting the mode to PLE is not required since reading any LEF or capTbl will make RC default to PLE which is indeed the recommended mode. Here are some articles from http://support.cadence.com that may be of interest to you

     

    87%
    How is cell area picked in RC-PLE flow?

     

    During optimization with PLE mode does RC use the lib area or lef area? Also is there a way to force RC to use the LEF area? Using the LEF area is supported in 7.1 and is default in this version.
    Show Attributes

    10-27-2009
    84%
    RC PLE: Cell area for macros is shown as zero. Why?

     

    Shouldn't the area be taken from .lib in absence of LEF information? As per the current behavior, if physical information or LEF for some macros are missing then their area will be shown as 0. The area of 0 is expected when LEF for the corresponding macros have not been read in.
    Show Attributes

    10-01-2008
    73%
    What can go wrong if the cell areas in Liberty library are different from LEF?

     

    Problem: What can go wrong if the cell areas in Liberty library are different from LEF? Solution: RC uses the area numbers from the LEF files when the LEF files have been read in.
    Show Attributes

    07-07-2010
    70%
    Does RC use cell areas from LEF or from Liberty in PLE mode?

     

    Problem: Does RC use cell areas from LEF or from Liberty in PLE mode? Solution: The cell dimensions defined in the LEF will be used if the LEFs have been imported and the tool is in PLE mode.
    Show Attributes

    02-02-2009

     

    regards,

    gh-

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