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Cannot find a legal location....

trigger

 Hi there, 

 during floorplan using FE I get the following warning message :

**WARN: (SOCSP-270):    Cannot find a legal location for MASTER CELL BUX20. Check the library cell definition and floorplan.

Actually  I got plenty of these messages for a different cells...Could You point me to a document or guide where I'll be able to read more about this warning...or give some explanation about it?

I'm confused cause  when I'm running the script (I'm using scripts for every step for the digital flow - synthesis, floorplan, placement, etc...) on another machine which actually uses a little older version of the FE I do not get this message...so I do not know which one is correct and what causes the warning message...I'll be glad on any help...

Thanks for Your time,

Regards... 

 

 

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  • TomBelpasso

    Strictly speaking, the SITE definintions do not have to be in the technology LEF, the first LEF file in the list of lefFiles.  But they must be defined before being used in any of the LEF files.  The site definition (from memory) would look like:

    SITE core

    CLASS CORE ;  # can be also be PAD or COVER, blocks nolonger need sites

    SIZE <x> <y> ;  # placer expects that x dimension will be smaller then y for horizonal row sites

    SYMMETRY Y ;   # legal values are X Y and R90, but only use Y for horizontal row libraries

    END core

     

    Note the SYMMETRY for sites has a different meaning then it has for cells.  Normally only use SYMMETRY Y, which would allow flipping (mirroring) in the Y dimension in rows.  If you specify X it would allow the cell to flip upside down in a North or R0 row , which can cause power shorts. 

    For cells it is a list of allowed orientations, so if you want cells to be placed in upside down rows, be sure to allow X  for cells.  If you want to allow mirroring of cells, then allow Y for cell symmetry.

    I know this is confusing, the developer of LEF want to save a token, so reused the SYMMETRY statement.  Not the best decision when viewed as a user.

    Regards,

    - Tom Belpasso

    Integrated-Vision.com

Reply
  • TomBelpasso

    Strictly speaking, the SITE definintions do not have to be in the technology LEF, the first LEF file in the list of lefFiles.  But they must be defined before being used in any of the LEF files.  The site definition (from memory) would look like:

    SITE core

    CLASS CORE ;  # can be also be PAD or COVER, blocks nolonger need sites

    SIZE <x> <y> ;  # placer expects that x dimension will be smaller then y for horizonal row sites

    SYMMETRY Y ;   # legal values are X Y and R90, but only use Y for horizontal row libraries

    END core

     

    Note the SYMMETRY for sites has a different meaning then it has for cells.  Normally only use SYMMETRY Y, which would allow flipping (mirroring) in the Y dimension in rows.  If you specify X it would allow the cell to flip upside down in a North or R0 row , which can cause power shorts. 

    For cells it is a list of allowed orientations, so if you want cells to be placed in upside down rows, be sure to allow X  for cells.  If you want to allow mirroring of cells, then allow Y for cell symmetry.

    I know this is confusing, the developer of LEF want to save a token, so reused the SYMMETRY statement.  Not the best decision when viewed as a user.

    Regards,

    - Tom Belpasso

    Integrated-Vision.com

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