Derek Hines-Mohrman

10/05/2021, 7:29 PM
Hello, I have a minor issue with Xschem/Sky130/ngspice integration. I was trying to get everything installed (on my CentOS VM) just this weekend and the recent video was very helpful. After following the new installation procedure, some of the test simulations did not work out of the box. In the example pictures below, I was running the test_nmos test, but the same issue appears in the pmos and biploar test. When the issue happens, a warning message appears saying some sky130 PR cell is being re-dfined as shown in Picture 1. Soon after, the simulation fails as shown in Picture 2. This issue can be fixed by removing the
statement which includes the cell in question (found in the nfet_20v0_MODEL script in this case). This needs to be done individually for each simulation. It seems the TT_MODELS script is sufficient to import the PR cells in the case of the NMOS simulation. After this change, the simulation appears to run without issue as shown in Picture 3. Editing the scripts is not a big deal for me, but I am concerned this might indicate something wrong in my ngspice or open_pdks installation. I could not find an explination for this in any Xscheme or ngspice tutorial I have watched. Do you know what might cause this issue? Where should I check for more details?