# OpenVAF and OSDI

OpenVAF compiles Verilog-A compact models into OSDI libraries. Monata keeps
model preparation separate from simulation: registry/cache/compiler APIs can
prepare explicit `.osdi` paths, and the native ngspice backend loads only the
paths passed through `SimTask.osdi_paths`.

```python
task = SimTask(
    circuit=circuit,
    analysis_spec=ACSpec(start=1, stop=1e9, points=100),
    output_names=["out"],
    osdi_paths=["models/bsimcmg.osdi"],
)
```

For each path, Monata emits a `pre_osdi <path>` command before the ngspice
analysis command. Missing files fail before launching ngspice with
`metadata["reason"] == "model_missing"`.

## Registry and Cache

Use `ModelRegistry` for explicit model asset lookup:

```python
from monata.models import ModelRegistry

models = ModelRegistry()
models.register("mos", "models/bsimcmg.osdi", module_name="bsimcmg")
osdi_paths = models.osdi_paths("mos")
```

As a convenience, `ModelRegistry()` can discover existing `.osdi` files from
`MONATA_OSDI_PATH` and selected installed-tool locations. For reproducible
project workflows, prefer explicit registration or explicit search paths so the
resolved model set is not an accident of the local shell environment.
Discovered models must still be passed explicitly into `SimTask`.

`ModelCompiler` wraps OpenVAF for explicit `.va` to `.osdi` compilation, and
`ModelCache` stores content-hash-based outputs. Standard Monata tests use fake
or mocked OpenVAF commands; real OpenVAF smoke checks are environment-gated.

Still deferred:

- implicit `.va` compilation during simulation
- automatic PDK technology binding beyond explicit registry/search paths
- simulator-specific plugin flows outside ngspice