set the channel description: Collecting information about LVS errors and how to analyze LVS logs automatically to explain the logs

Ok, my idea is the following: We collect a list of LVS issues, with a clearly identified root cause, the left and right netlist, and the LVS report.

I will then try to develop a tool which parses the reports and searches for such issues, and if such an issue is found, it will try to explain the likely root cause for the issue to the user and suggest ways to check and fix it.

I think for a start we should start with LVS reports that contain only a single root cause. Later on we will also need LVS reports that contain several root causes at the same time.

So for every submission I will need an in-depth explanation what the root cause actually was, which hints in the LVS report were helpful for you to identify it. It would be also interesting if there were any misleading hints in the LVS reports (false-positives), ...

If possible it would be good if you could share the design files (physical and schematic). Feel free to send them to me with private messages under NDA.

Beware. . . I used to use a commercial LVS tool that attempted to do this, and was so bad at it that it was not worth looking at its laughable "recommendations". Just to point out that it is not a trivial problem to solve. . .

I fully understand that it's not trivial at all, but I would like to give it a try.

It’s really helpful when the left and right side of the netgen report match with similar names, and kind of confusing when it doesn’t. Enhancing netgen is one option, but having an interactive post processing tool might also work. Maybe netgen already has this capability - I haven’t used interactive tracing. For example:

Circuit 1: sky130_fd_sc_hvl__lsbufhv2lv_1                                         |Circuit 2: sky130_fd_sc_hvl__lsbufhv2lv_1

---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Net: a_30_1337#                                                                   |Net: a_30_1337#
  sky130_fd_pr__pfet_g5v0d10v5/(1|3) = 1                                          |  sky130_fd_pr__pfet_g5v0d10v5/(1|3) = 1
  sky130_fd_pr__nfet_g5v0d10v5/2 = 2                                              |  sky130_fd_pr__nfet_g5v0d10v5/2 = 2
  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 1                                          |  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 1
  sky130_fd_pr__pfet_g5v0d10v5/2 = 1                                              |  sky130_fd_pr__pfet_g5v0d10v5/2 = 1
                                                                                  |
Net: VGND_uq0                                                                     |Net: VGND
  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 2                                          |  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 4
  sky130_fd_pr__nfet_01v8/(1|3) = 1                                               |  sky130_fd_pr__nfet_01v8/(1|3) = 1
                                                                                  |
Net: VNB                                                                          |Net: VNB
  sky130_fd_pr__nfet_g5v0d10v5/4 = 4                                              |  sky130_fd_pr__nfet_g5v0d10v5/4 = 4
  sky130_fd_pr__nfet_01v8/4 = 1                                                   |  sky130_fd_pr__nfet_01v8/4 = 1
                                                                                  |
Net: a_30_207#                                                                    |Net: a_30_207#
  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 1                                          |  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 1
  sky130_fd_pr__nfet_g5v0d10v5/2 = 1                                              |  sky130_fd_pr__nfet_g5v0d10v5/2 = 1
  sky130_fd_pr__pfet_g5v0d10v5/(1|3) = 1                                          |  sky130_fd_pr__pfet_g5v0d10v5/(1|3) = 1
                                                                                  |
Net: a_389_1337#                                                                  |Net: a_389_1337#
  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 1                                          |  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 1
  sky130_fd_pr__pfet_01v8_hvt/2 = 1                                               |  sky130_fd_pr__pfet_01v8_hvt/2 = 1
  sky130_fd_pr__pfet_01v8_hvt/(1|3) = 1                                           |  sky130_fd_pr__pfet_01v8_hvt/(1|3) = 1
---------------------------------------------------------------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Net: VPWR_uq0                                                                     |(no matching net)
  sky130_fd_pr__pfet_g5v0d10v5/(1|3) = 1                                          |
                                                                                  |
Net: VPWR                                                                         |(no matching net)
  sky130_fd_pr__pfet_g5v0d10v5/(1|3) = 1                                          |
---------------------------------------------------------------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Net: A                                                                            |Net: A
  sky130_fd_pr__pfet_g5v0d10v5/2 = 1                                              |  sky130_fd_pr__pfet_g5v0d10v5/2 = 1
  sky130_fd_pr__nfet_g5v0d10v5/2 = 1                                              |  sky130_fd_pr__nfet_g5v0d10v5/2 = 1
                                                                                  |
Net: VPB                                                                          |Net: VPB
  sky130_fd_pr__pfet_g5v0d10v5/4 = 2                                              |  sky130_fd_pr__pfet_g5v0d10v5/4 = 2
                                                                                  |
Net: VGND                                                                         |Net: VPWR
  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 2                                          |  sky130_fd_pr__pfet_g5v0d10v5/(1|3) = 2
---------------------------------------------------------------------------------------------------------------------------------------------------------------------

In the first and third section, the only difference is in

VGND

. A filtered report might look like

Circuit 1: sky130_fd_sc_hvl__lsbufhv2lv_1                                         |Circuit 2: sky130_fd_sc_hvl__lsbufhv2lv_1

---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Net: a_30_1337#                                                                   |Net: a_30_1337#
Net: VGND_uq0                                                                     |Net: VGND
  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 2                                          |  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 4 *
  sky130_fd_pr__nfet_01v8/(1|3) = 1                                               |  sky130_fd_pr__nfet_01v8/(1|3) = 1
                                                                                  |
Net: VNB                                                                          |Net: VNB
Net: a_30_207#                                                                    |Net: a_30_207#
Net: a_389_1337#                                                                  |Net: a_389_1337#
---------------------------------------------------------------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Net: VPWR_uq0                                                                     |(no matching net)
  sky130_fd_pr__pfet_g5v0d10v5/(1|3) = 1                                          |
                                                                                  |
Net: VPWR                                                                         |(no matching net)
  sky130_fd_pr__pfet_g5v0d10v5/(1|3) = 1                                          |
---------------------------------------------------------------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Net: A                                                                            |Net: A
Net: VPB                                                                          |Net: VPB
Net: VGND                                                                         |Net: VPWR
  sky130_fd_pr__nfet_g5v0d10v5/(1|3) = 2                                          |  sky130_fd_pr__pfet_g5v0d10v5/(1|3) = 2
---------------------------------------------------------------------------------------------------------------------------------------------------------------------

Splitting into 2 files and using vimdiff to highlight the differences might work too. Incidentally, this is a case where disconnected nets with the same label in the layout match one net in the schematic.

One important thing to do, which I have not done yet, is to take the output of netgen using the

debug on

command in the setup (which dumps a ton of data), and drop that information into the JSON file format, and get the GUI viewer to filter that output in a sensible way. Currently,

debug on

only produces text output, and does not add to the JSON output, although the information is just an additional level of hierarchy to the output and lends itself to JSON better than it does to text output, which gets so messy that it is practically unreadable. @Mitch Bailey: I wrote some additional output formatting into netgen so that it will attempt to match the columns on each side, but if net names are different on each side, then it quickly gets lost. The additional information cited above that is output by the

debug

option is looking deeper into the connectivity trees, so that's additional information that could be used for better matching. It's also really easy to end up with a matching algorithm that runs O(N^2) and drags netgen down to a crawl.

My idea is to start with clearly defined errors ("attached pin to the wrong device", "short-circuit between 2 nets", ...), and first try to detect the patterns these errors have in the LVS log-files, and then filter away any false positive patterns that we have in other LVS logs. For the pattern matching my current idea is to load the complete debug JSON output from Netgen into a graph database like neo4j so that we can define the positive and negative patterns as queries on the graph.

Clean shorts and opens are easy to detect. The worst issue is that any error that touches a power supply (which happens rather too often) causes a lot of output, since the power supplies touch nearly all devices. Then it becomes a matter of ignoring all the output entries that have the same power supply difference.