2026-06-15 11:32:12 +02:00
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# 11 — Re-enable the SPICE simulator
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2026-07-19 15:59:21 +02:00
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> **DONE (2026-07-17), as a worker service rather than a static link — see
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> [docs/features/ngspice-split/](../ngspice-split/README.md).** The analysis
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> below predates the implementation; the "static link into eeschema.wasm"
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> recipe it recommends was superseded by the occ_service-style split (crash
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> isolation, lazy loading, and an in-service solution for XSPICE's .cm dlopen
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> via a static code-model registry). The ~25-line `init_dll()` edit happened
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> as predicted; `KICAD_SPICE=OFF` and the model-data stubs are gone.
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2026-06-15 11:32:12 +02:00
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## Current state (more nuanced than "KICAD_SPICE=OFF")
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- `-DKICAD_SPICE=OFF` in `build-kicad-target.sh` is **vestigial** — there's no such option in
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this KiCad (only `KICAD_SPICE_QA`). The simulator is *always* built; all `eeschema/sim/`
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sources compile for wasm.
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- The dep is satisfied by a header-only stub: `wasm/cmake/Findngspice.cmake` points includes
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at `wasm/stubs/ngspice/sharedspice.h` with an empty link line.
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- **Runtime kill-point:** `SIMULATOR_FRAME` ctor → `NGSPICE` init → `ngspice.cpp:474`
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`m_dll.Load(wxDynamicLibrary::CanonicalizeName("ngspice"))` fails (no `dlopen` without
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`-sMAIN_MODULE`) → throws → caught at `eeschema/eeschema.cpp:208-221` → simulator silently
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returns `nullptr`.
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## The groundwork already here
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- **A wasm ngspice build script exists:** `scripts/deps/build-ngspice.sh` (ngspice 45.2,
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static, cider + xspice, pthread; opt-in via `build-all-deps.sh --with-ngspice`).
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- **A known size landmine is already handled:** the 4 giant model-data initializers
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(`sim_model_ngspice_data_{bsim4,b3soi,b4soi,hsim}.cpp`) exceeded the JS engines' "too many
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locals" validation limit and are stubbed (`eeschema/CMakeLists.txt:292-305` +
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`wasm/stubs/eeschema_ngspice_data_stubs.cpp`).
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## Why static linking works
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KiCad resolves 9–11 ngspice function pointers via `GetSymbol` (`ngspice.cpp:503-517`) and
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registers C callbacks (`cbSendChar`, `cbBGThreadRunning`, … `ngspice.cpp:519`). With a
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**statically linked** `libngspice.a`, those become plain function pointers and direct symbol
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references — no `dlopen` needed. Threading: KiCad drives sims via `bg_run`/`bg_halt`
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(`ngspice.cpp:335,342`) using ngspice's internal pthread; the wasm build is already
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full-pthread, and native code already assumes callbacks fire on the bg thread — same model.
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Precedent (all static, OpenMP off, shared-lib mode unsupported under emscripten):
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wokwi/ngspice-wasm, EEcircuit (eelab-dev), danchitnis/ngspice, plus upstream ngspice WASM
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patches (#96, #99).
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## Recipe
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1. Verify `scripts/deps/build-ngspice.sh` completes for 45.2.
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2. Make `wasm/cmake/Findngspice.cmake` return the **real** sysroot lib + headers when present
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(fall back to the stub otherwise).
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3. **The one unavoidable upstream-file edit:** a `#ifdef __EMSCRIPTEN__` branch in
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`eeschema/sim/ngspice.cpp` `init_dll()` that binds the `m_ngSpice_*` pointers directly to
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the statically-linked symbols instead of via `wxDynamicLibrary` (~25 lines, one block).
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4. Ship `spinit` / `.cm` codemodels into MEMFS if xspice device models are wanted.
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5. **Retest the model-data stubs** — the "too many locals" failure predates the now-default
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post-asyncify `wasm-opt -O2` pass that solved the same engine-limit family elsewhere (see
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the `chrome-asyncify-rewind-crash` memory). If it's resolved, restore the 4 real model-data
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files; if not, the simulator works minus BSIM4/SOI/HSIM device models.
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## Residual risks (verify at runtime)
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- `SIMULATOR_FRAME`'s plot widget behavior under wxUniversal (untested).
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- Asyncify vs. the ngspice bg-thread interplay during a running simulation (see the
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[async dossier](../async/README.md) for the suspension model).
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Diff impact: ~25 lines in one upstream file (`ngspice.cpp`) + a `Findngspice.cmake` change
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(wasm layer). Everything else is the dep build and FS assets.
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