194 lines
12 KiB
Markdown
194 lines
12 KiB
Markdown
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# Circuit Emulation — Architecture
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## High-level data flow
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Two pipelines coexist. Both share the same `avr8js` harness and the same Arduino program fixtures; they differ only in the analog solver.
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```
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┌────────────────────────── Shared ──────────────────────────┐
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│ │
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│ Arduino sketch source (.ino) or pre-built .hex │
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│ │ │
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│ ▼ │
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│ ┌─────────────┐ │
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│ │ AVRHarness │ (wraps avr8js) │
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│ │ (CPU + │ │
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│ │ PORTs + │ │
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│ │ ADC + │ │
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│ │ Timers) │ │
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│ └──────┬──────┘ │
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│ │ │
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│ pin state / PWM duty ADC channel voltages │
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│ ▼ ▲ │
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└──────────────────│────────────────────│─────────────────────┘
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│ │
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┌──────────────┼────────────────────┼──────────────┐
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│ ▼ │ │
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│ ┌─────────────────┐ │ │
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│ │ Pipeline A │ │ │
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│ │ MNA Solver (JS) │──────────┤ │
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│ │ │ │ │
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│ │ - Node graph │ │ │
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│ │ - Stamps │ │ │
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│ │ - Newton loop │ │ │
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│ │ - Transient │ │ │
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│ │ (back-Euler) │ │ │
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│ └─────────────────┘ │ │
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│ │ │
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│ ┌──────────────────┐ │ │
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│ │ Pipeline B │ │ │
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│ │ SpiceEngine │─────────┘ │
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│ │ (eecircuit-engine│ │
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│ │ / ngspice-WASM) │ │
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│ │ │ │
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│ │ - Netlist in │ │
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│ │ - ResultType out │ │
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│ │ - AVRSpiceBridge │ │
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│ │ for co-sim │ │
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│ └──────────────────┘ │
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│ │
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└──────────────────────────────────────────────────┘
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```
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## Module layout
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```
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test/test_circuit/
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├── src/
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│ ├── solver/ # Pipeline A — hand-rolled MNA
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│ │ ├── linalg.js # Gaussian elimination with partial pivoting
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│ │ └── Circuit.js # Circuit class, DC + transient solve
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│ ├── components/ # Component library for Pipeline A
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│ │ ├── passive.js # R, V, I, C, Pot, NTC, Switch
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│ │ └── active.js # Diode, LED, BJT
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│ ├── avr/ # Shared AVR harness
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│ │ ├── intelHex.js # Intel HEX parser (same format as Velxio)
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│ │ ├── AVRHarness.js # Thin wrapper over avr8js
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│ │ ├── asm.js # Mini AVR assembler (LDI, OUT, STS, LDS, RJMP, SBRC/S, NOP)
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│ │ └── programs.js # Hand-assembled Arduino programs (pot→PWM, adcRead)
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│ ├── spice/ # Pipeline B — ngspice integration
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│ │ ├── SpiceEngine.js # runNetlist() + vec()/dcValue() helpers
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│ │ └── AVRSpiceBridge.js # Quasi-static AVR ↔ ngspice co-simulation
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│ └── index.js # Re-exports for Pipeline A
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├── fixtures/
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│ └── blink.hex # Copied from frontend/src/__tests__/fixtures/
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├── test/ # 14 test files, 47 tests total
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├── plan/ # 8 markdown planning docs
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└── autosearch/ # 4 findings docs
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```
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## Pipeline A — Hand-rolled MNA
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Goal: a transparent, minimal-dependency baseline that we fully control. Useful for:
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- Understanding every step of the solver
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- Cross-checking ngspice results on toy problems
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- Providing a fallback if `eecircuit-engine` cannot be loaded in a constrained environment
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**Execution path:**
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1. User constructs a `Circuit` object and adds `Component` instances.
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2. `circuit.solveDC({maxIter, tol})` is called.
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3. Solver identifies voltage-source components and allocates extra MNA rows.
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4. For each Newton iteration:
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- Zero the G matrix and b vector (size `N + M`).
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- Add a small shunt conductance `GMIN = 1e-12` on every node for stability.
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- Call `component.stampDC(G, b, ctx)` on every component.
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- Solve `G · x = b` via Gaussian elimination.
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- Apply damping (≤ 0.5 V step per node) and iterate until `max |Δx| < tol` or `maxIter` reached.
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5. Store `nodeVoltages` and `branchCurrents` in `state`.
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**Transient execution path:**
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1. `circuit.runTransient(tEnd, dt, sampleEvery)` seeds `state.prev.nodeVoltages` from each capacitor's `Vinit` (the initial condition).
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2. On every step, `state.prev` is the solution from the previous step.
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3. The capacitor stamp uses backward Euler: conductance `G_c = C/Δt`, companion current `I_eq = (C/Δt)·V_prev`.
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4. Solver runs `solveDC({dt})` with the capacitor stamps using `ctx.prev`.
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See [circuit-emulation-mna-solver.md](circuit-emulation-mna-solver.md) for stamp-level detail.
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## Pipeline B — ngspice-WASM
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Goal: leverage the full, battle-tested ngspice engine (30+ years of development) without reinventing any physics.
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**Execution path:**
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1. First call to `getEngine()` or `runNetlist()` boots `eecircuit-engine` — downloads and instantiates ~39 MB of WASM+glue; takes ~400 ms.
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2. Subsequent calls reuse the same `Simulation` singleton.
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3. Each call:
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- Compose a full SPICE netlist string (component cards + `.op` / `.tran` / `.ac` / `.dc` + `.end`).
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- `sim.setNetList(netlist)`.
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- `await sim.runSim()` → returns a `ResultType` with `variableNames[]` and `data[].values[]`.
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4. Our wrapper exposes helpers:
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- `vec(name)` → array of numbers (real data) or `[{real, img}]` (complex data from `.ac`).
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- `dcValue(name)` → first value of the vector.
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- `findVar(name)` → index in `variableNames[]`, matching either `"v(node)"` or just `"node"`.
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See [circuit-emulation-ngspice.md](circuit-emulation-ngspice.md) for netlist authoring conventions and gotchas.
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## Mixed-signal co-simulation
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`avr8js` runs the MCU at ~1 MHz (in JS it's slower than real 16 MHz silicon, but cycle-accurate). ngspice runs transient analysis on the analog network. They are **not locked cycle-by-cycle**; instead the bridge operates **quasi-statically** in time slices.
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Per slice (default: 1 ms of AVR time = 16 000 cycles):
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```
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┌─ slice n ────────────────────────────────────────────────┐
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│ │
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│ 1. avr.runCycles(16_000) │
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│ → new pin states, new PWM duty cycles │
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│ │
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│ 2. snapshot = { pin6:{type:'pwm',duty:0.5}, │
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│ pin13:{type:'digital',v:5}, ... } │
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│ │
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│ 3. buildNetlist(snapshot) → string │
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│ V_PIN6 pin6 0 DC 2.5 ← duty × 5 │
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│ V_PIN13 pin13 0 DC 5 │
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│ ... passive circuit ... │
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│ .tran 10u 1m │
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│ .end │
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│ │
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│ 4. await runNetlist(netlist) → result │
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│ │
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│ 5. for each analog channel: inject final v(node) into │
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│ avr.setAnalogVoltage(ch, v) │
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│ │
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└──────────────────────────────────────────────────────────┘
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```
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This is good enough for:
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- ADC sampling of slow analog sources (NTC, pot, photoresistor)
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- PWM filtered to DC via RC
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- LED current driven by a digital or PWM pin
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- Digital outputs driving logic or switches
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It is **not good enough** for:
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- Audio-rate feedback loops where the analog network reacts on sub-millisecond timescales
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- Oscillators where the analog side drives a digital input and vice versa with tight timing
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- Noise / jitter analysis
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For the tight-coupling cases, a co-simulation framework would need to arbitrate time advancement between the two engines (see [Velxio Integration](circuit-emulation-velxio-integration.md) for future work).
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## Shared Arduino harness
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Both pipelines use `AVRHarness` to drive `avr8js`. This class **mirrors exactly** what Velxio's `frontend/src/simulation/AVRSimulator.ts` does:
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- `new CPU(programUint16, sramBytes)`
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- `new AVRIOPort(cpu, portBConfig/portCConfig/portDConfig)`
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- `new AVRADC(cpu, adcConfig)` — `adc.channelValues[channel] = volts` to inject analog
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- `new AVRTimer(cpu, timer0Config/...)`
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- `new AVRUSART(cpu, usart0Config, 16_000_000)`
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- Listeners per port: `port.addListener((newValue, oldValue) => ...)` with bit-by-bit diff and Arduino pin mapping (D0–D7, D8–D13, A0–A5 via port C).
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- PWM duty read via `cpu.data[ocrAddress]` where ocrAddress for Timer0A is `0x47`, Timer1AL is `0x88`, etc.
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This parity is important: any lesson learned in the sandbox transfers one-for-one to Velxio's main app.
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See [circuit-emulation-avr-bridge.md](circuit-emulation-avr-bridge.md) for the full harness reference.
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## Fixtures and hand-assembled programs
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To exercise the full sketch path (C++ → avr-gcc → hex) we would normally compile Arduino code. The sandbox does not have `avr-gcc` installed, so we use:
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1. **Copied from Velxio**: `fixtures/blink.hex` — the same Intel HEX used by `frontend/src/__tests__/fixtures/avr-blink/avr-blink.ino.hex`. Tests that load this file exercise the full Arduino core init (reset vectors, library init, `setup()`, `loop()`).
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2. **Hand-assembled programs**: `src/avr/programs.js` exposes `potToPwmProgram()` and `adcReadProgram()`, built with the mini-assembler in `src/avr/asm.js`. These bypass the Arduino core and directly configure ADC and Timer0 registers. They produce ~18–22 instruction words each. Full opcode breakdown is in [circuit-emulation-appendix.md](circuit-emulation-appendix.md).
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