Replacing Cells with Black Boxes

The Analyzer provides the ability to replace specified cells with black boxes effectively removing them from the netlist. Cells replaced by a black box are not loaded by the Analyzer, though you can specify port characteristics allowing the Analyzer to validate the cell's interface to other circuitry.

When to use Black Boxes

Specifying black boxes may be appropriate for cases when a netlist contains complex cells that do not require validation in order to optimize processor and memory usage and improve runtimes. Examples might be a netlist containing a synthesized RTL block generated in an all-digital design flow or a large pre-compiled memory containing billions of transistors.

How to Specify Black Boxes

Black boxes are specified as part of netlist load process by selecting the "Pause for cell review" option in the GUI or by using the -blackBoxing option of the csrc load API command.

  • When invoked through the GUI, the Analyzer will stop after a short pre-scan and present a dialog where cells can be marked for replacement and their port characterisitcs specified. You can find details on using Cell Review in the Loading a Netlist chapter of the User's Manual.

  • When using the API, the -blackBoxing option is used to specify a Tcl proc that defines black boxes using csrc modify commands. The proc will be executed during netlist load to make the specified changes. You can find details on using the -blackBoxing option of the csrc load command in the API Reference.