Differential pair tuning claims different lengths before and after tuning

[Kyle Owen]

I am tuning a differential pair, matching the length to a manually-set value. Upon tuning the untuned trace, it turns green when it's added enough meanders, and I click the left mouse button to accept it. Upon clicking it again to confirm the tuned length, it says it's too short, even though it was exactly correct, supposedly, in the previous tuning step. Now that it claims it's too short by less than 1 mm, it's impossible to match exactly with the desired settings. What should I believe? This seems to happen on nearly all of my tuned traces.

Application: kicad
Version: 4.0.5 release build
wxWidgets: Version 3.0.2 (debug,UTF-8,compiler with C++ ABI 1002,GCC 4.2.1,STL containers,compatible with 2.8)
Platform: Mac OS X (Darwin 13.4.0 x86_64), 64 bit, Little endian, wxMac
Boost version: 1.57.0
         USE_WX_GRAPHICS_CONTEXT=ON
         USE_WX_OVERLAY=ON
         KICAD_SCRIPTING=ON
         KICAD_SCRIPTING_MODULES=ON
         KICAD_SCRIPTING_WXPYTHON=ON
         USE_FP_LIB_TABLE=HARD_CODED_ON
         BUILD_GITHUB_PLUGIN=ON

[Tomasz Wlostowski (twlostow)]

Hi Kyle,

Can you send us the board that shows the issue?

Cheers,
Tom

[Kyle Owen (drovak-deactivatedaccount)]

Yes, here's the layout in question. Using 4.0.4 on my Windows 10 machine, I didn't see the same issue with a completely new layout, though I did check the lengths of those pairs and confirmed that they were not in fact equal to the longest trace.

[Jeff Young (jeyjey)]

It's been over a year and there are no other reports of this. Was it fixed at some point?

[Jeff Young (jeyjey)]

@Tom. (Ping.)

[Kyle Owen (drovak-deactivatedaccount)]

Sorry for not getting back to you sooner; haven't done any differential
routing lately...so I can't say for certain.

Kyle

On Fri, May 18, 2018 at 12:20 PM, Jeff Young <email address hidden>
wrote:

> @Tom. (Ping.)
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1656950
>
> Title:
> Differential pair tuning claims different lengths before and after
> tuning
>
> Status in KiCad:
> New
>
> Bug description:
> I am tuning a differential pair, matching the length to a manually-set
> value. Upon tuning the untuned trace, it turns green when it's added
> enough meanders, and I click the left mouse button to accept it. Upon
> clicking it again to confirm the tuned length, it says it's too short,
> even though it was exactly correct, supposedly, in the previous tuning
> step. Now that it claims it's too short by less than 1 mm, it's
> impossible to match exactly with the desired settings. What should I
> believe? This seems to happen on nearly all of my tuned traces.
>
> Application: kicad
> Version: 4.0.5 release build
> wxWidgets: Version 3.0.2 (debug,UTF-8,compiler with C++ ABI 1002,GCC
> 4.2.1,STL containers,compatible with 2.8)
> Platform: Mac OS X (Darwin 13.4.0 x86_64), 64 bit, Little endian, wxMac
> Boost version: 1.57.0
> USE_WX_GRAPHICS_CONTEXT=ON
> USE_WX_OVERLAY=ON
> KICAD_SCRIPTING=ON
> KICAD_SCRIPTING_MODULES=ON
> KICAD_SCRIPTING_WXPYTHON=ON
> USE_FP_LIB_TABLE=HARD_CODED_ON
> BUILD_GITHUB_PLUGIN=ON
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/kicad/+bug/1656950/+subscriptions
>

[Seth Hillbrand (sethh)]

Confirmed still happening with test board in #2

Application: pcbnew
Version: (6.0.0-rc1-dev-467-gb8d0c199c)-1, release build
Libraries:
    wxWidgets 3.0.2
    libcurl/7.52.1 OpenSSL/1.0.2l zlib/1.2.8 libidn2/0.16 libpsl/0.17.0 (+libidn2/0.16) libssh2/1.7.0 nghttp2/1.18.1 librtmp/2.3
Platform: Linux 4.9.0-8-amd64 x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.2 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
    Boost: 1.62.0
    OpenCASCADE Community Edition: 6.8.0
    Curl: 7.52.1
    Compiler: GCC 6.3.0 with C++ ABI 1010
Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=OFF
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=OFF

[KiCad Janitor (kicad-janitor)]

KiCad bug tracker has moved to Gitlab. This report is now available here: https://gitlab.com/kicad/code/kicad/-/issues/1838