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Restructure

Restructure is an interface to ABC for local resynthesis. The package allows logic restructuring that targets area or timing. It extracts a cloud of logic using the OpenSTA timing engine, and passes it to ABC through blif interface. Multiple recipes for area or timing are run to obtain multiple structures from ABC; the most desirable among these is used to improve the netlist. The ABC output is read back by a blif reader which is integrated to OpenDB. blif writer and reader also support constants from and to OpenDB. Reading back of constants requires insertion of tie cells which should be provided by the user as per the interface described below.

Commands

Restructuring can be done in two modes: area or delay.

Area Mode

restructure -liberty_file <liberty_file>
            -target "area"
            -tielo_pin  <tielo_pin_name>
            -tiehi_pin  <tiehi_pin_name>

Timing Mode

restructure -liberty_file <liberty_file>
            -target "delay"
            -slack_threshold <slack_val>
            -depth_threshold <depth_threshold>
            -tielo_pin  <tielo_pin_name>
            -tiehi_pin  <tiehi_pin_name>

Argument Description:

  • liberty_file Liberty file with description of cells used in design. This is passed to ABC.
  • target could be area or delay. In area mode, the focus is area reduction and timing may degrade. In delay mode, delay is likely reduced but area may increase.
  • -slack_threshold specifies a (setup) timing slack value below which timing paths need to be analyzed for restructuring.
  • -depth_threshold specifies the path depth above which a timing path would be considered for restructuring.
  • tielo_pin specifies the tie cell pin which can drive constant zero. Format is lib/cell/pin
  • tiehi_pin specifies the tie cell pin which can drive constant one. Format is lib/cell/pin

Example scripts

Regression tests

Limitations

FAQs

Check out GitHub discussion about this tool.

Authors

  • Sanjiv Mathur
  • Ahmad El Rouby

License

BSD 3-Clause License. See LICENSE file.