Can I get a clarification on

.param mc_mm_switch=0

. I think it's only required when I'm using the sky130 libraries? Are there any docs about what it does? Also, I have 2 computers, one needs the param set to simulate, the other doesn't. Both are using the same xschem and pdk version.

From the name, it has something to do with enabling Monte Carlo variations in the models. What it does EXACTLY is only clear when looking into the model files.

@Matt Venn when you add the

.lib /.../.../pdk/sky130A/libs.tech/ngspice/sky130.lib.spice tt

the specified corner (

tt

) is read from the file:

* Typical corner (tt)
.lib tt
.param mc_mm_switch=0
.param mc_pr_switch=0
* MOSFET
.include "corners/tt.spice"
* Resistor/Capacitor
.include "r+c/res_typical__cap_typical.spice"
.include "r+c/res_typical__cap_typical__lin.spice"
* Special cells
.include "corners/tt/specialized_cells.spice"
.endl tt

You see the .lib file sets the montecarlo / mismatch switches to zero. The

tt_mm

mismatch corner sets one of these switches:

* Typical corner with mismatch (tt_mm)
.lib tt_mm
.param mc_mm_switch=1
.param mc_pr_switch=0
* MOSFET
.include "corners/tt.spice"
* Resistor/Capacitor
.include "r+c/res_typical__cap_typical.spice"
.include "r+c/res_typical__cap_typical__lin.spice"
* Special cells
.include "corners/tt/specialized_cells.spice"
.endl tt_mm

and the Montecarlo corner (

mc

) sets the other:

* Monte Carlo process variation

.lib mc

.param mc_mm_switch=0
.param mc_pr_switch=1

.include "parameters/critical.spice"
.include "parameters/montecarlo.spice"

.endl mc

So as far as I know you should not need to set these parameters yourself.

Thanks Stefan. It's odd that on my PC I have to set one or the sim fails. On the laptop I don't.

@Matt Venn very likely on one pc the .spiceinit file is missing. This file must be present in the directory where ngspice runs and should contain the following lines:

set ngbehavior=hsa
set ng_nomodcheck 
set num_threads=4

The last line is optional, The first one is very important, since it tells ngspice the .lib file format to use (hspice-like)

good idea, but I have it commited to my repo to avoid this