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Guild: wafer.space Community
Channel: 🏗️ - Designing / project-template / Antenna violations
After: 10/31/2025 23:59
Before: 12/01/2025 00:00
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[11/19/2025 20:47] mithro_



[11/19/2025 20:47] mithro_
I think @Leo Moser (mole99) mentioned we need to look into why antenna violations are appearing.

OpenROAD is suppose to produce DRC clean results and I believe it should be doing so for GF180MCU.


[11/19/2025 21:43] rzioma
I have a similar issue: 11 net and 10 pin violations.

Couldn’t fix them regardless of parameters I have tried so far.


[11/19/2025 21:44] rzioma
AntennaRepair step reports that it fixed all the issues, but antenna check afterwards finds the same issues 🤷‍♂️


[11/19/2025 21:49] rzioma
Also I can’t seem to find a way to enable pass that does INSERT_ECO_DIODES


[11/20/2025 08:19] mole99
Before the second shuttle, I would like to investigate why these antenna violations occur. This can be either a limitation of OpenROAD or a misconfiguration in LibreLane. I will need to compare this with ORFS to see if it produces fewer or no antenna violations when using the open source PDKs.
A small number of low-ratio antenna violations will most likely not cause any problems. Tiny Tapeout has been doing this from the start.

Nevertheless, there are a few things you can do to reduce the antenna violations.

1. You can increase the number of antenna insertion iterations and the margin to overfix them.

These are the default values:

```yaml
GRT_ANTENNA_ITERS: 3
GRT_ANTENNA_MARGIN: 10 # %
```

2. You can manually insert antenna diodes.

```yaml
# https://librelane.readthedocs.io/en/latest/reference/api/steps/index.html#librelane.steps.ECODiode
INSERT_ECO_DIODES:
 - target: "bidir[0].pad/A"
 - target: "bidir[1].pad/A"
```

For this to take effect, you also need to add the `Odb.InsertECODiodes` step to the flow.

```yaml
meta:
  version: 3
  flow: Chip
  substituting_steps:
    ...
    +OpenROAD.GlobalRouting: Odb.InsertECODiodes
    ...
    
    (or after detailed routing)
    
    ...
    +OpenROAD.DetailedRouting: Odb.InsertECODiodes
    ...
```


[11/20/2025 11:32] mithro_
@Leo Moser (mole99) - OpenROAD has a pretty big CI system


[11/20/2025 11:32] mithro_
https://dashboard.precisioninno.com/trends

{Embed}
https://dashboard.precisioninno.com/trends
OpenROAD Dashboard
OpenROAD Dashboard

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[11/20/2025 11:58] rzioma


{Attachments}
2025-11_media/image-9E495.png


[11/20/2025 11:59] rzioma
@Leo Moser (mole99) it looks adding `DRT_ANTENNA_REPAIR_ITERS: 10` did the trick!
Those elusive antennas were result of Detailed Routing. I think that explains why cranking up `GRT_ANTENNA_MARGIN` wouldn't do much for me.

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[11/20/2025 12:01] rzioma
In contrast my awkward attempts at `INSERT_ECO_DIODES` eventually did fix the antennas, but made LVS to fail 😐


[11/20/2025 12:01] rzioma
@Leo Moser (mole99) Thanks for OpenROAD.**Detailed**Routing: Odb.InsertECODiodes tip. Got me thinking! 🙂


[11/20/2025 12:04] rzioma
@LukeW could you try `DRT_ANTENNA_REPAIR_ITERS: 10` and see if it helps you too?


[11/20/2025 12:05] rzioma
Now lets see if DRC is going to pass :awkwardsweat:


[11/20/2025 12:43] _luke_w_
Thanks, my report was with the unmodified template repo, I haven't been running the klayout DRC for development. I can take a look later on tonight.


[11/20/2025 14:29] mole99
@ReJ aka Renaldas Zioma I'm wondering how you found out about `DRT_ANTENNA_REPAIR_ITERS`? By chance?
Because it's not yet in the docs, as it was a pretty recent addition to LibreLane :)

The only reason I can think of for why `DRT_ANTENNA_REPAIR_ITERS` is 0 by default is because the whole rip-up and partial routing was quite buggy in OpenROAD until recently. But it seems that it works mostly fine now? If so, I can add this as a default option to the template and we can see how well it fixes antenna violations in different designs.


[11/20/2025 14:33] rzioma
@Leo Moser (mole99) by reading logs :awkwardsweat:

There was a warning in the log after detailed routing that DRT_ANTENNA_REPAIR_ITERS is set to 0 and the pass going to be skipped.


[11/20/2025 14:36] mole99
Haha, I see 😄 Well done!
I think I'll enable antenna repair after DRT in the template by default. If OpenROAD crashes, we can disable it again. If partial route produces strange results, LVS will alert us.

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[11/20/2025 21:55] mithro_
@Leo Moser (mole99) - Do we have a tracking bug for the antenna stuff somewhere?


[11/20/2025 21:57] mithro_
@Leo Moser (mole99) - BTW The OpenROAD team owes me a few favours (but they are quite busy), so if we need anything from them it should be pretty easy to get fixes done.


[11/21/2025 00:37] _luke_w_
Just to confirm, `DRT_ANTENNA_REPAIR_ITERS: 10` fixes my antenna violations

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[11/21/2025 06:02] mole99
I will open a LibreLane PR to enable `DRT_ANTENNA_REPAIR_ITERS` by default so that we can track any regressions through the LibreLane CI.


[11/21/2025 06:03] mole99
There might be a different issue that I would like to get fixed by the OpenROAD team. I'll let you know 👌🏻


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