Meander is a pain in the neck

[HarrySatt]

Hi there

Everyone satisfied with what FUSION360 is selling us as MEANDER tool? I am not. The on the fly calculation is definitely wrong. I have browser open and the length is different on the diff net but shown in the on fly calculation as 100% and 100%. Changing not possible, because only undo is possible. What the hack is this tool for. Only for making us crazy about FUSION360 but not happy.

Regards, Harald

[jorge_garcia]

Hi @HarrySatt ,

Thanks for reaching out. I think some explanation is in order, by default the meander tool will match the lengths of the diff pair to the longer of the two members that's why you see the percentages. The value of above the percentages is the length being matched to which by default is the longer of the two segments.

Now what if you want to match to a specific length? All you have to do is type the length you want in the command line and press enter while the meander command is active. You'll notice the value above the percentages update to the length you just entered. As you add lengths the percentages will update until the two lengths are equal or very nearly so(you can set the tolerance in the DRC misc tab).

Let me know if you continue to run into problems.

Best Regards,

[HarrySatt]

Yes. But still it is hard to use this tool. Might need some rework. From my point of view it should be easier to set the length to a fixed value to make it possible to design equal long traces for a number of differential nets. F.e CameraLink where 5 matched differential pairs need to be equal length with matched impedance. This is with the current approach not easy by the best.

What I would like to see is a command where I can fix the length and the meander is done more or less automatically and can be adjusted afterwards what now is not possible. Also I think meander should not interfere with coupling of the pair (see below)

From Channel Link Design Guidelines from NatSemi. As you can see one of the not recommended routing for differential pairs is  the way eagle solves meandering.

Regards @jorge_garcia , Harald

[HarrySatt]

Hi @jorge_garcia 

Have a look into this YT video. See how KiCAD does differential pair routing

https://www.youtube.com/watch?v=chejn7dqpfQ

This would be nice to see in FUSION360. It has all of the features high speed designers are looking for.

Regards, Harald

@RichardHammerl 

[rachaelATWH4]

That does look better that what you can do in EAGLE and Fusion Electronics with just the Meander tool, and that's a video from 2015! It's something I struggled with a lot doing complex memory interfaces in EAGLE. I ended up writing a ULP to give some additional functionality to help drive the meander tool based from maximum lengths within a selected bus but it was far from perfect. I really hope the Fusion Electronics team can give a significant improvement in the meander functionality fairly soon as we can see it's years behind even KiCAD!

Best Regards,

Rachael

[jorge_garcia]

Hi @rachaelATWH4 , Hi @HarrySatt ,

I'd like some clarification in order to provide feedback for improvement. I watched the entire video, the only advantage I see in KiCADs implementation is the menu to specify the parameters of the coil. In the rest of the process I just see lots of key presses and clicks.

This makes me think that either I missed something or our diff pair and meander commands need much better documentation. In Fusion 360 if you need to deskew, just right click and do asymmetrcial meandering with the meander command active. No need to have a separate command.

To specify the matching length you type it in the CLI and press enter, no need for a separate menu. In our implementation the coils automatically adjust their height and number to get equalization, subject to a gap factor setting and DRC(this is the area where I see KiCAD's implementation as superior). You don't need to manually increase or decrease the number of coils nor do you need to manually adjust their height.

So I ask, what did I miss or misunderstand? I watched the entire video, and the biggest advantage I saw was in the much clearer constraint setup. You can define the default height, bend radius, etc. of the coils. For Fusion, I think it would be better to set up a Max height and minimum coil radius and then leverage the automation to put in the coils like we do now. Our current Gap Factor+Netclasses+DRC approach is more cumbersome and I recognize that.

Thanks in advanced for the feedback.

Best Regards,

[erik.hole]

I agree with @HarrySatt that the diff routing tools in F360 are next to useless. This might be as you say @jorge_garcia because of lack of documentation, but every time I've tried to route with the diff pair tool, I've ended up just routing them manually at matching the trace length from the design manager, which is an aweful work flow.

Something should be improved on the diff pair / meandering side. Either improvements in implementation flow, or in documentation.

Best regards,

Erik Hole

[HarrySatt]

Hi @jorge_garcia 

You are right for sure that this tool need a proper description in the user manual. differential pairs , deskew and with that the meandering is getting more and more necessary because of rising data frequency. So a easy and intuitive tool is  mandatory. The routing should be somewhere equivalent to routing a single wire, meaning all the parameters should be able to be set ( rectangular, angle or free and so on ). Also should the meandering also be possible on angled differential pairs, moving of a dp should be possible for both in one or single (this you can do in KiCAD).

I think AUTODESK can do much better than what is given to the user up to now.

See also a short YT video about behavior of meander in an angled part of a DP. It is not working as you can see.

https://youtu.be/qymxbS9dA2Y

Please DO SOME WORK on this.

Regards, Harald

@erik.hole 

@rachaelATWH4 

@RichardHammerl 

[jorge_garcia]

Hi @HarrySatt ,

Thanks for all of your feedback. You have inspired me to take some time to make a video on the meander command. 

@HelenChen-ElectronicsQA This looks like a bug, that changes on the perpendicular segment should stay but they don't. It's worth trying to make a reproducible case.

Best Regards,

[rachaelATWH4]

This is definitely a bug. I have just replicated it on a board I am working on at the moment which might become an issue fairly soon when I get properly into the routing.

Best Regards,

Rachael

[Anonymous]

I just wanted to add to the conversation and say that with the latest version of Fusion 360 Electronics (July 14th 2021) I'm unable to persist a meander that is placed on a differential pair between CPU and RAM. I am able to create the meander but when I left click to complete the operation, it disappears. Am I doing something wrong? I did watch the video from 2020 on diff pairs but I'm not getting the same behavior with the meander tool. Is it possible that the meander tool cancels the meander operation if it feels the diff pair is matched within a certain tolerance? If so - some feedback from the app would be appreciated. 

[rachaelATWH4]

It's not just you it's definitely broken as shown in the videos from @HarrySatt and myself above. Hopefully they'll get this fixed fairly quickly as it's clearly a bug in the tool.

Best Regards,

Rachael

[HelenChen-ElectronicsQA]

Hi @HarrySatt , @rachaelATWH4 , @jorge_garcia ,

So sorry for my late response that I missed this post and I just got chance to revisit it today.

For the issue @HarrySatt shown in the video, there is a workaround to bypass it:

Switch to Ignore Violators (Alt + I) from the default Push Violators during meandering before placing the meandered routes, then it should work.

I will log a ticket to check with our developer to see whether anything wrong here. 

Thank you so much.

Additionally, I took the screenshot of the help doc of Meander in EAGLE for your reference.

Hope it helps a little.

Regards,

Helen

[HarrySatt]

Hi

That nice. for the first it is OK. Maybe this should be the default behavior for meander.

Regards, Harald.

[HelenChen-ElectronicsQA]

Hi @HarrySatt ,

Thank you very much for your feedback.

Do you mean you are expecting it's Ignore Violators mode by default when running meander?

Regards,

Helen

[HarrySatt]

Yes or give a hint on using the MEANDER command like "You are set to
avoid violators. That might show unexpected behaviour" but I think
better is to ignore violators.

regards, Harald

[HelenChen-ElectronicsQA · Accepted solution]

Hi @HarrySatt ,

Thank you very much for your suggestion. I will feedback to our team.

Currently please turn off Push Violators when meander code for 45 angled wires as the workaround. 

So sorry for any inconvenience and please feel free to let us know if you have anything need our further assistant. 

Regards,

Helen

[motla.design]

---

@jorge_garcia wrote:

our diff pair and meander commands need much better documentation

---

Hi @jorge_garcia thank you for your implication on Fusion360. You wrote this in 2021 however the documentation for the meander tool is still non-existant in the Fusion360 documentation. I know maybe few users use this command, but really what you have to do is just copy/paste the documentation from the Eagle documentation.

Fusion360 documentation pages on Meander:

- https://help.autodesk.com/view/fusion360/ENU/?guid=ECD-MEANDER-ABOUT

- MEANDER command https://help.autodesk.com/view/fusion360/ENU/?guid=ECD-LAYOUT-EDITOR

Eagle documentation (there is a whole section, see 6.10 Differential Pairs And Meanders on page 223)

https://www.rikmed.com/downloads/manual_en.pdf

Also the documentation in the toolbox restricts to differential pairs, although this can be sufficient in basic setups, the MEANDER command can do much more. Most of the time we have to route much more than 2 signals to the same length (ULPI, RMII, SDMMC, .....). However you restricted the docs and tutorials to differential pairs.

[motla.design]

That's a shame because the MEANDER tool is quite easy and pleasant to use once you know how to use it, but it is written nowhere in Fusion360.

Some basic instructions:

- make sure you selected "Ignore Violators" mode in the bottom toolbar (it may also work in other modes but it's less practical)

- type "MEANDER 50mm" with the desired trace length in the command line (alternatively select Meander in route/rework menus and type only the desired trace length).

- click on a wire, at the desired start of the meander

- move the cursor away, it will create a meander and will tell you the percentage of error

- if you want the meander to be on one side only (non symmetrical), right click

- left click to finish

To know the current length of a wire, just don't provide length when calling MEANDER, then click on the wire.

As easy as that.

[jorge_garcia]

Hello @motla.design,

Admittedly this is tricky to find but if you look on this page it contains a lot of what you mentioned
https://help.autodesk.com/view/fusion360/ENU/?guid=ECD-CLI#meander

I'll pass your feedback along to our documentation expert to see if there is a way to surface this information more readily.

Let me know if there's anything else I can do for you.

Best Regards,