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#analog-design
Title
# analog-design
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bluecmd

10/03/2020, 5:38 PM
There seems to be three open-source alternatives to schematic capture that I can see, (1) xschem (2) electric, (3) geda-gaf (gschem). The last one is pretty hard to find info about, and seems to not be packaged for Ubuntu anymore.
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Tim Edwards

10/04/2020, 12:01 AM
You're missing xcircuit. . .
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bluecmd

10/04/2020, 7:56 AM
Thanks!
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Pepijn de Vos

10/04/2020, 8:04 AM
I'm currently playing with eeschema. As far as I'm aware none of them already have Sky130 symbols. https://twitter.com/pepijndevos/status/1312400527611834370
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bluecmd

10/04/2020, 8:04 AM
Nice! Very cool!
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Pepijn de Vos

10/04/2020, 8:05 AM
Everyone I talk to seems to think it's unsuitable for asic though... we'll see
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bluecmd

10/04/2020, 8:06 AM
Right, i was going to ask - the rumor is that kicad is not great for vlsi - but I honestly don't know what that actually means.
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Pepijn de Vos

10/04/2020, 8:09 AM
Apparently it's not great at hierarchy and swapping out implementations. https://skywater-pdk.slack.com/archives/C016HUV935L/p1601725733109300
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bluecmd

10/04/2020, 8:15 AM
Very good, I agree on all those points with using xschem
My finger memory from using Virtuoso 8 years ago kicked in when I started playing with it
It feels very VLSI:y and the Gaw integration is pure genius
Getting a few extra side developers to help @Stefan Schippers and the Gaw author (don't know who that is from the top of my head) to grind away some edges would be all that's needed to make it a top notch tool I think
Right now it's a bit like a Gentoo installation, you have to tweak it and some things you'll have to do just right, but when you have it working it is fast and stable :-). But we need to make it as easy as Ubuntu!
@Pepijn de Vos how did you get the sky130 transistor into eescheme?
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Pepijn de Vos

10/04/2020, 8:25 AM
I did this one manually by taking the MNMOS from the legacy PSICE folder and then edited it to use the sky130 model. You can see the parameters in the second screenshot in the Twitter thread.
My plan is to see if I can generate a library, and then try and do a design with it.
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No doubt xschem is the best and most mature tool we have right now. However, I'm not sure "exactly like Virtuoso" is what I would consider a compliment, because it's the very reason I'm here and not working at NXP right now. I think the Gentoo analogy is accurate, but I'm not convinced it'll ever make it to the Ubuntu part. I briefly looked at the source code, and have zero interest in contributing to it, and have the deepest respect for those who do.
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bluecmd

10/04/2020, 8:42 AM
Sure, and that's the wonderful nature of open-source - there will be alternatives for people who don't like one certain tool 🙂
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Stefan Schippers

10/04/2020, 9:27 AM
@Pepijn de Vos, @bluecmd see here the reason for xschem 🙂 definitely not 'exactly like Virtuoso' thats really not a compliment... may be only some UI interactions are a bit familiar to people who have worked on cadence.
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bluecmd

10/04/2020, 9:28 AM
Thanks! Sorry, didn't meant to insult xschem, but it certainly felt familiar to Virtuoso, which I think is a good thing!
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Pepijn de Vos

10/04/2020, 9:35 AM
I think you are right. I think the "can not handle complex VLSI designs" could be a bit more substantiated to solidify the argument. Strong hierarchy support was mentioned. What else? Personally I'm only doing "very small system integration" so I'm not yet hitting any barriers with eeschema, which seems more intuitive to me.
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bluecmd

10/04/2020, 9:38 AM
It needs to have a black background. Can't have VLSI without a black background. 😉
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yrrapt

10/04/2020, 10:32 AM
@Pepijn de Vos Regarding the virtuoso-likeness, that matters a lot if you use virtuoso all day and then need to context switch to the click happy kicad paradigm. Like I said before, it doesn't matter to everybody but it does to some people. But there is no right answer, just use what you want to use
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Stefan Schippers

10/04/2020, 11:46 AM
@bluecmd xschem has also a 'light colorscheme 🙂 (View -> Toggle colorscheme) however i agree with you, background needs to be black for VLSI/ASIC :-)
@bluecmd for ASIC/VLSI i should add in the list Tim Edward's xcircuit and remove gschem/lepton-schematic. From my tests gschem (or its fork, lepton-schematic) has serious limitations: • time to do simple operations like move, select, select by area, delete grows exponentially as circuit grows, this is certainly not good, and i suspect due to excessive usage of scheme scripting (lists) • There is no concept of 'logical net' as all the backend for that is done by gnetlist. For gschem nets are just segments. This makes it difficult to do things like 'highlight' a net and follow it thru a hierarchical design. Kicad's eeschema is much better in handling big designs, however its memory footprint is enormous, it is easy to grow to several gigabytes with big schematics. Not a major issue with today harwdare anyway. Xcircuit is also good at big designs and hierarchy, its interface is veeeery different from what people used to do on commercial tools (mostly cadence) so you need to get used to it. Best in class for graphic quality as it uses postscript natively for file format.
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bluecmd

10/04/2020, 12:04 PM
Thanks! Yes, I added it when Tim let me know about it
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Stefan Schippers

10/05/2020, 2:19 PM
@bluecmd in this video some of the issues i have when managing big schematics, this one is about kicad's eeschema.
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bluecmd

10/05/2020, 3:44 PM
Very impressive @Stefan Schippers!
Some good engineering work there