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When I use LibreLane to generate a small digital module, everything looks normal but there is no metal fill, whereas I noticed that the top design in the template does have metal fill. What is causing this difference?

First thought would be different hardening strategies in the config.json, but could be wrong (https://librelane.readthedocs.io/en/latest/usage/caravel/index.html)

I don't know, I don't see any configuration related to metal fill in template's config.yaml. And the fillers are successfully inserted, but no metal fill.

I see, the template uses the chip flow, which calls some KLayout scripts to insert metal fill. In my case, I didn’t explicitly set any flow, so I assume it’s using the default classic flow, which doesn’t seem to run the KLayout density/metal-fill steps. If I want to add metal fill for a small standalone digital block, what is the recommended approach?

Normally, you wouldn't run metal fill for a standalone block. One way to do that, however, is to add the KLayout.Filler step after one the StreamOut steps in the Classic flow. You can do this directly in the config.

Thanks! May I ask how to do that directly in the config?

You can find the relevant docs here: https://librelane.readthedocs.io/en/latest/usage/writing_custom_flows.html By using substituting_steps and placing a "+" before the step ID. You're welcome!

Thank you!