Differential Pair Skew Tuning Issues

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1

Strange issue when applying skew rule to differential pairs. (KiCAD 9.0.6 WIn11)

The skew tool works as expected, each pair P/N have the same length (within the max set skew).

However when running DRC it shows errors stating that the skews are out of range and that the target length is from a different differential pair.

In my attached example I have 3 IC’s each with a differential pair, the differential pair on IC1 has no errors, the ones on IC2 & IC3 show errors with the skew.

For some reason the DRC is taking the length of the net 1_P as being the target length rather than other track in the same differential pair.

Differential Pair.zip (178.1 KB)

2

Looks like this is an old issue, seems that specifying a netclass doesnt compare within the differential pair.

So changing my rule to the below fixed the issue.

(rule "max_skew"
    (constraint skew (max 0.1mm) (within_diff_pairs)))

What I had previously was:

#LVDS Skew
(rule "LVDS Skew"
	(condition "A.NetClass == 'LVDS'")
	(constraint skew(opt 0mm) (max 0.1mm)))
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