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Guild: wafer.space Community
Channel: ℹ️ - Information / ⁉️-questions / Failing Hold Checks
After: 2025-11-30 11:59 p.m.
Before: 2026-01-01 12:00 a.m.
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[2025-12-03 7:56 p.m.] trev5514
Has anyone been able to pass timing for hold checks on an 11MHz+ design? I have done everything I could think of, yet the corners still end up failing. The path is always pad -> reg nothing else.

I've tried these settings:

PL_RESIZER_HOLD_SLACK_MARGIN from 0.1, 0.3, 0.5 even 0.7 and none seem to make a difference (I do get less hold errors but all still fail)
I've tried PL_RESIZER_ALLOW_SETUP_VIOS

and

set_input_delay -min 0, .5, 1, 1.5

Any ideas?


[2025-12-03 8:08 p.m.] mole99
Perhaps an unbalanced clock tree? You can view the clock tree in OpenROAD GUI.


[2025-12-03 8:12 p.m.] ravenslofty
sure; I've passed hold checks on a 60MHz design :p


[2025-12-03 8:12 p.m.] ravenslofty
I do often need to ECO some hold buffers in though


[2025-12-03 8:18 p.m.] trev5514
With the exception of the right spot which I'll look into it looks very balanced.

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[2025-12-03 8:19 p.m.] trev5514
Do you manually place them in? Did you change your input/output delays or do you use the templates default 0 for min?


[2025-12-03 8:21 p.m.] ravenslofty
read `54-openroad-stapostpnr/summary.rpt` to find the failing corners, then look at `54-openroad-stapostpnr/<corner>/min.rpt` to find the failing paths, and then [follow the docs](https://librelane.readthedocs.io/en/latest/usage/using_ecos.html)


[2025-12-03 8:21 p.m.] ravenslofty
it's manual in that you have to point the tooling at the cell you want to insert a hold buffer for, but there's no physical placement or such

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[2025-12-03 8:25 p.m.] trev5514
Thank you, I have been looking at those corners but I didn't know about the ECO step!


[2025-12-03 8:26 p.m.] ravenslofty
(the downside of having a 60MHz design is that I have basically given up on meeting slow corner setup without major cheating)


[2025-12-03 8:27 p.m.] trev5514
My original target was 90MHz and now I'm just trying to get any passing. I'm currently failing 10MHz...


[2025-12-03 8:28 p.m.] ravenslofty
are you using the 9-track libraries?


[2025-12-03 8:31 p.m.] trev5514
Whatever the default one is.


[2025-12-03 8:33 p.m.] ravenslofty
7-track. Try adding `STD_CELL_LIBRARY: gf180mcu_fd_sc_mcu9t5v0` to your `librelane/config.yaml`

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[2025-12-03 8:35 p.m.] trev5514
I'll give it a go after I try ECO. Surely 10MHz is possible with the 7-track? At this point - what do I know haha!


[2025-12-03 8:56 p.m.] trev5514
@Lofty Did you ever run into unconnected ECO pins after the eco step?


[2025-12-03 9:08 p.m.] trev5514
Looks like the disconnected pins are pwr/gnd: eco_buffer_0/VDD, eco_buffer_0/VNW, eco_buffer_0/VPW, and eco_buffer_0/VSS


[2025-12-03 9:12 p.m.] greg.hashtag.9468
What does your I/O connect to? If it's not actually driven synchronously alongside your clock input. You may be able to further relax the timing.
With a `input_delay -min 0` you're telling the tools, the external i/o arrives with the clock. So it tries to add 4ns of delay to ensure a leaf in your clock tree.


[2025-12-03 9:14 p.m.] trev5514
Everything is synchronous with the clock input.


[2025-12-03 10:38 p.m.] polyfractal
(oof, did not know about ECO or 9T stuff either. probably would have saved a lot of agony fussing with settings 😅 )


[2025-12-03 10:39 p.m.] trev5514
Maybe, ECO isn't working for me still and neither is the 9T


[2025-12-03 10:50 p.m.] trev5514
For anyone that runs into the ECO issue:

"+OpenROAD.DetailedRouting": "Odb.InsertECOBuffers"
 "+Odb.InsertECOBuffers": "OpenROAD.DetailedRouting"

I haven't confirmed yet, but I added the Odb.InsertECOBuffers step but I didn't add the routing after which likely left the ECO buffers unconnected.


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