Sudden "Voltage node does not have DC path to ground"

[Shridhar Ambady]

Hi everyone,

I recently got Sky130 set up and I've been using Xyce in Xschem and suddenly today I can't run any simulations because of this error.

I reopened a simple curve sweeper I used last week, absolutely no settings have been changed, all of this was working just a couple days ago, and even this circuit gets the same error. I've tried restarting to no luck.

I'm running Ubuntu on WSL through MobaXterm. The error also appears when I run the .spice netlist through Xyce in the command line, so I don't think it's a Xschem issue, but I am also having a strange new issue at the exact same time where ngspice no longer outputs any files even if it successfully runs

Anybody seen this suddenly pop up? Is it just some weird permissions thing or some bash command I need to run?

Any help appreciated, thank you!

[Francesc Serra-Graells]

Hi Shridhar Ambady,

It looks like all your circuit nodes (including GND) are floating. Xyce ground is node 0 by definition.

I do not use Xschem, but maybe it shows up now because of a change in the Xschem netlisting procedures so GND is not mapped to 0 anymore...

Alternatively, you can try to add

.PREPROCESS REPLACEGROUND TRUE

so Xyce will replace GND by 0 (User Guide Section 13.2).

Best regards,

Paco

El dia dimecres, 17 d’agost de 2022 a les 17:02:33 UTC+2, samba...@gmail.com va escriure:

[Stef]

The problem is that GND is an alias for '0' in ngspice and it is not in Xyce.
ngspice behavior is non standard and can be disabled:

*no_auto_gnd* Setting this boolean variable by set no_auto_gnd in spinit or .spiceinit,
ngspice will refrain from replacing all nodes named gnd by node 0. In using this
setting, you will have to take care of proper zeroing appropriate ground nodes. If
you fail to do so, ngspice may crash, or deliver wrong results.

To fix the issue in any existing schematics or netlists add a 0V voltage source between nodes '0' and 'GND'
Stefan

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[xyce-users]

As a previous commenter noted, Xyce can support GND as a synonym for node 0, using the relevant PREPROCESS command.

It just isn't Xyce's default behavior.  So this can be fixed either way.

Eric

[Shridhar Ambady]

The preprocess command fixed it, thank you so much!!

Now I'm wondering why it was working well without issue in the first place 🤔