kicad-developers team mailing list archive

[Wayne Stambaugh <stambaughw@xxxxxxxxx>]

On 8/29/2018 2:43 PM, Seth Hillbrand wrote:
> 
> 
> Am Mi., 29. Aug. 2018 um 11:04 Uhr schrieb Wayne Stambaugh
> <stambaughw@xxxxxxxxx <mailto:stambaughw@xxxxxxxxx>>:
> 
>     On 8/29/2018 12:22 PM, Simon Richter wrote:
>     > Hi,
>     >
>     > On 28.08.2018 21:56, Anthony Tonizzo wrote:
>     >
>     >> Recently during the manual layout of a board with many
>     >> differential pairs I noticed that there was no button to add
>     >> a diff-pair the way there is a button for regular tracks.
>     >> Rather, adding diff-pairs is currently accomplished using
>     >> a menu entry.
>     >
>     > I dimly remember that diff-pair mode should be used automatically
>     if the
>     > net name ends in "_P", "_N", "+" or "-", as a substitute for a proper
>     > "diff-pair" flag in the netlist.
>     >
>     >    Simon
>     >
> 
>     I thought this was documented as well but a quick scan of the KiCad
>     documentation turned up empty.  AFAIK, this behavior is still in play.
> 
>     Wayne
> 
> 
> Does this mean we should be expressly dis-allowing single-track routing
> on a differential pair?  The current behavior is that differential pair
> routing is only allowed on the net pairs named as Simon mentioned but we
> do not automatically use differential pair routing in those cases.

I don't know if we want to open up that can of worms.  It probably makes
sense but I can for see where someone mistakenly uses the _P/_N or +/-
nomenclature and forcing the dp router may not be what the user
intended.  I'm not opposed to the idea.  I just foresee issues if we
implement this.  Maybe a compromise behavior is to fire up the dp router
by default but allow the user to fall back to single trace routing upon
request if that is not what the user intended.  Although that may be
more effort to code than it's worth.

> 
> I think that this behavior is correct until we have designated
> differential pairs in our file formats.

Until file formats support diff pairs, we are always going to have some
users that will take sides about this behavior.

> 
> -Seth