Using .spiceinit Files

Introduction

The .spiceinit component lets you add custom ngspice or SpiceOpus startup commands to a QUCS-S schematic. It is available from the SPICE netlist sections category of the Components Tab.

Warning

If you are using hierarchical design/QUCS-S subcircuits, place the .spiceinit component in the top-level schematic (not the lower-level subcircuit schematics) or you may get unpredictable behavior.

How QUCS-S Regenerates .spiceinit at Simulation Time

Warning

Before each simulation, QUCS-S deletes any existing .spiceinit file in the working directory it uses for the external SPICE simulators. It then writes a new local .spiceinit there only if there is content to include: a selected Compatibility Mode directive, an active .spiceinit schematic component, or both. If neither is present, no local .spiceinit is written.

This delete-and-regenerate behavior applies to both ngspice and SpiceOpus.

Note

For ngspice specifically:

• When QUCS-S writes a local .spiceinit, ngspice loads that file instead of $HOME/.spiceinit.

• When QUCS-S writes no local .spiceinit, ngspice falls back to its normal startup-file lookup, which may include $HOME/.spiceinit.

Tip

Environment variables are unaffected by this behavior: QUCS-S launches the simulator with the environment it was itself started in, so any environment variables referenced from within included SPICE files are still inherited normally.

Use Cases

Selecting an ngspice Compatibility Mode

One use for the .spiceinit component is enabling an ngspice Compatibility Mode for a particular schematic, by placing a compatibility command (such as set ngbehavior=ltpsa) inside it. See SPICE Model Compatibility Modes & Troubleshooting for the full explanation of these modes and when they’re needed.

Resolving External Model References with sourcepath

If your model files depend on additional ngspice startup commands beyond a Compatibility Mode — for example, a sourcepath entry so a bare .include or .lib reference can be resolved — add those commands to the schematic’s .spiceinit component so they are included whenever QUCS-S writes a local .spiceinit, rather than relying on $HOME/.spiceinit.