Custom design rule for Differential pair

[Jay_Khandekha]

Hello,
i am using kicad version 6.0.2, i am setting custom rule for diffrerntial pair. i want to assign different trace width, diff pair gap & clearence to individual nets.
I have tried this.
(version 1)
(rule "diffpair"
(layer F.Cu)
(constraint diff_pair_gap (min 0.4mm))
(constraint track_width (min 0.1mm))
(constraint clearance (min “0.05mm”))
(condition “A.inDiffPair(‘USB’)”)
)
But i am not getting result for specific net.(condition “A.inDiffPair(‘USB’)”).
How can i assign the constraint to a specific net?

[albin]

I haven’t tried this myself yet, but maybe the answer is in this thread?

[solved] Custom differencing rule not working [DRC]

I am trying to make a rule to control each differential pair in each different layer, however following the documentation I do not find any result [image] This is an example to comply with the documentation. (version 1) (rule “space between tracks” (condition “A.inDiffPair(‘USB’) && AB.isCoupledDiffPair()”) (constraint diff_pair_gap(min 0.35mm)) ) As you can see the tracks belong to a differential pair (USB_P and USB_N), however this rule does not apply. but if I use the condition (’…

[Jay_Khandekha]

I tried this one also but still it is not working.

[maykol_rey]

don’t use “USB” use “/USB”

[Jay_Khandekha]

Trird this one also but still it is not working.

[maykol_rey]

Try the same rule that you put, your problem is the name of the differential pair, if you use “USB_P” and “USB_N”, your selector must be “USB_”

[gkeeth]

@Jay_Khandekha

(version 1)
(rule "diffpair"
(layer F.Cu)
(constraint diff_pair_gap (min 0.4mm))
(constraint track_width (min 0.1mm))
(constraint clearance (min “0.05mm”))
(condition “A.inDiffPair(‘USB’)”)
)

Your rules worked for me if I added an (opt <desired value for the router to use>) token to the diff_pair_gap constraint.

min/max are used by DRC only, and opt is the value that the router uses when you’re routing.

So I did:

(version 1)
(rule "diffpair"
	(layer F.Cu)
	(constraint diff_pair_gap (min 0.4mm) (opt 0.43mm))
	(constraint track_width (min 0.1mm))
	(constraint clearance (min "0.05mm"))
	(condition "A.inDiffPair('/usb_')")
)

With those rules the router automatically put the traces 0.43mm apart, regardless of what I had set in the netclass DP settings, and DRC was clean. I found the Constraint Resolution tool to be really helpful here - initially I had the diff pair name wrong and it told me that my rule was not applied to the selected trace, which tipped me off to the problem.

P.S. I didn’t check the track width and clearance but I think those would also be set automatically by the router if you put in an opt token to those constraints.

[Jay_Khandekha]

Thank you for the reply.
I tried same thing but it is still not working.
I am using kicad in ubuntu, so is there any issue regarding OS?

[gkeeth]

I doubt this is OS-specific. Could you share your design, stripped down if necessary?

At least sharing a screenshot of the traces and net names would be helpful.

[Kharar]

Alternatively you could assign your differential pairs to a dedicated net class and then substitute
(condition "A.inDiffPair('/usb_')")
with
(condition "A.NetClass == 'your_netclass'")

[Jay_Khandekha]

Thank you @Kharar
I tried this one & this is working properly.
(version 1)
(rule “diffpair”
(layer F.Cu)
(constraint diff_pair_gap (opt 0.1mm))
(constraint track_width (opt 0.1mm))
(constraint clearance (opt 0.1mm))
(condition “A.NetClass == ‘Diff_100_OHM’”)
)

[Kharar]

You are welcome @Jay_Khandekha

Now for the mystery of why the other approach didn’t work for you:

As you can see above I have a differential pair named TD0_N and TD0_P that are defined from a sub sheet named LAN, so in order to use the name correctly I would have to include the path prefix.
Like this: (condition "A.inDiffPair('/LAN/TD0_')")

If this doesn’t help can you maybe find your net and post us a screenshot of that, like the above?