Netclass Constrain Maker Plugin

This KiCad plugin analyzes netclasses in your PCB and generates custom DRC rules based on each netclass's maximum trace length. It also provides an interface that lets you filter and view detailed information about your netclasses and their associated nets.

Special thanks

This approach to manually modify (key 7, tune length of single track) the length of a track and thus be able to define the same distance for all tracks of the same netclass, comes from the solution proposed by JamesJ in the Kicad forum discussion

Features

1. Netclass Listing: Displays each netclass and the nets that belong to it.
2. Net Length Calculation: Computes the total length (in mm) of each net.
3. Filtering: Allows you to display only those netclasses specified by the user.
4. DRC Rule Generation: Creates (rule ...) blocks for KiCad, setting the detected maximum length as a constraint.
5. "ALL" Button: Shows all netclasses without filtering.

Installation Instructions

Copy NetclassInfoPlugin.py to the scripting/plugins path, in my case it would be in this path

C:\Users\Jairo\Documents\KiCad\8.0\scripting\plugins.

Plugin Usage

1. Open your project in KiCad and go to the PCB Editor.
2. Navigate to Tools > external plugins, or to the plugins section (depending on your KiCad version).
3. Select "Netclass Information" from the list of available plugins (or from the contextual menu, if configured).
4. A window will appear containing:
   • A text field to enter Netclass Names (comma-separated).
   • A main text area showing the information.
   • Buttons: Filter, ALL, Show DRC Rules, and Close.

Interface Details

• Enter Netclass Names (comma-separated)
  Use this field to type the netclass names you want to filter, separated by commas. Example: PWM, USBC, Vin

• Filter Button
  Displays information only for the netclasses you entered.

  • You will see the list of nets associated with each netclass and their lengths.
  • You will also see the maximum length detected for each netclass.

• ALL Button
  Displays information for all netclasses detected in the PCB, without filtering.

• Show DRC Rules Button
  Generates (rule ...) blocks with the maximum length for each netclass currently shown in the window.

  • If you previously clicked Filter, only those filtered netclasses are included.
  • If you clicked ALL, rules are generated for every netclass.

• Close Button
  Closes the plugin window.

Example of Generated Rules

When you click Show DRC Rules, you get something like:

(version 1)

(rule PWM_LENGTH (condition "A.NetClass=='PWM'") (constraint length (opt 18.673mm)) )

(rule DATA_LENGTH (condition "A.NetClass=='DATA'") (constraint length (opt 25.500mm)) )

; -- End of generated DRC rules --

You can copy and paste this block into your KiCad DRC configuration file or integrate it however you prefer.

Final Notes

• You can modify the source code to change the (constraint length (opt ...)) to (max ...) or other KiCad options.
• The plugin does not automatically overwrite or modify your .kicad_drc file; it only shows the text for you to use manually.
• The length accuracy depends on how KiCad sums track segments and their bending radii (if applicable).

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Enjoy this plugin! Any feedback or improvements are welcome as issues or pull requests!