netgen infinite loop

[d-m-bailey]

Netgen 1.5.305 enters an infinite loop and prints

Flattening unmatched subcell ldo_OTA in circuit ldo (1)(0 instances)
Flattening unmatched subcell ldo_OTA in circuit ldo (1)(0 instances)
...

until the disk runs out of space.

ldo_OTA is explicitly preflattened in the setup file.

netgen_loop.tgz

tar xzf netgen_loop.tgz
cd netgen_loop
netgen -batch source lvs.script

Changing subckt ldo to ldo1 (and the instance) eliminates the problem.

cp chipation_A_track.ok.spice chipathon_A_track.spice
netgen -batch source lvs.script

(Actually, since there is no ldo1 in the layout, the ldo1 in the source is preflattened. However, changing ldo$x to ldo1$x in the extracted spice also completes.)

Years ago I think I remember reporting a similar problem with flatglob where a flatglob substring caused a cell containing that substring to be flattened. At the time, I think I was using the optimize. Someone (Leo?) tried to create a test case but we couldn't recreate the problem. I tried search but couldn't find the previous thread.

[RTimothyEdwards]

Looks like I had netgen improperly prohibiting the cell contents of cells in the "noflatten" list, rather than the cells themselves, in one place. The infinite loop problem fell out of that, although I took the opportunity to run a check on the condition that caused the looping, so it won't do it again should there be some other similar cause.

The LVS for this example still fails, but for reasons that at first glance appear to be related to the device names being extracted, not an issue with "noflatten" and/or failure to flatten or failure not to flatten. I am checking the updated code on some other examples and will push a fix shortly.

[RTimothyEdwards]

I do not think that the glob string is the problem; the search adds ^ to the front and $ to the end of each item in the file, so that (apart from internal glob special characters in the string), the name must be an exact match. However, in your file, you probably need to escape all the "$" with backslashes, because otherwise "$" is a glob special character. That is not the cause of the infinite loop, but probably explains the behavior with respect to changing "ldo$x" to "ldo1$x".

[RTimothyEdwards]

The "-noflatten" switch and "flatten prohibit" command appear to work correctly now, as far as I can tell. I have pushed the correction to the opencircuitdesign.com repository.

[RTimothyEdwards]

Or maybe I will have to wait until I get home tomorrow because my laptop seems to have an incorrect git config for netgen.

[d-m-bailey]

@RTimothyEdwards As always, extreme gratitude for the quick response.

And yes, the LVS configuration is far from complete.