Hi all, I need to know whether Antenna Violations should be zero in digital macros, or a small number of violations is ok.

They should be zero- Yes. It must be zero at all cost - No A small number is acceptable if the ratio is not a very large value

I got two violations. Now how can we check whether they are critical or not?

check this for how to read the antenna report

@Matt Venn Thanks, I am reading the guide above, so we stumble upon question " How do we know if they exceed limit". I will try to find it in above guide.

so that ratio is only 2x

@Matt Venn I'm still confused by that report. It says ratio 400... which is greater than 2.

My understanding is the first number has to be less than the 2nd

Which first and second numbers?

I'll try to clarify the page

It's it's 929 / 185 that is 5x

@Tayyeb Mahmood: The general principle here is that antenna violations will give you a yield hit---that's something to worry about on a production run because it will affect profit margins. But for a test chip on an MPW run, you could in principle have a yield loss as high as 10% and never notice it. So then it comes down mostly to personal choice. If the antenna violation is in a circuit that you think people will re-use as-is on other projects, then it would be in your best interest to knock the antenna violations down to zero. But it is most likely that the antenna violations occur in (1) a synthesized block which would most likely be resynthesized if re-used in another project, or (2) a top level layout which would necessarily be re-done for another project. That's the thinking behind my guidance.

@Tim Edwards Do you know how to read that report? "Area" vs "S.Area"? I understand C = cummulative.

@Matthew Guthaus: No, sorry, I was puzzling over that myself. "P" is for "partial" and "C" is for "cumulative". "S" is maybe "sidewall", but I'm not sure, since all of the metal calculations should be done on sidewall areas.

Yeah, I was trying to correspond it to the LEF calculation. The value of 400 seems like the S.Area compared to the the gate area is 400x which would be significant.

The 400 value is too much of a coincidence. . . I think it must be referring to the rule ratio (which is 400). That would make the 929 value the actual ratio, which is 2.3x over the rule limit, which is what Matt Venn was assuming. But that's just guesswork. Is that output format documented anywhere in the OpenROAD/OpenLane documentation?

I think this stuff is explained here and coded here.

Are you putting tap cells in your design?

Tap cells are part of user_proj_example (or macro hardening) flow. However, I was experimenting with MAGIC_DRC_USE_GDS setting that created problem. Setting it to 1 resolves the problem.

I've updated https://www.zerotoasiccourse.com/terminology/antenna-report/ to make it clearer and include Tim's latest advice