se.cherkasov
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Full NES emulation: CPU, PPU, APU, 47 mappers, iNES/NES 2.0 parsing. GTK4 desktop client with HeaderBar, pixel-perfect Cairo rendering, drag-and-drop ROM loading, and keyboard shortcuts. 187 tests covering core emulation, mappers, and runtime.
108 lines
4.5 KiB
Markdown
108 lines
4.5 KiB
Markdown
# Architecture
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This document describes how the workspace is organized internally.
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Use `../README.md` for project overview, `integration.md` for host integration, and `api_contract.md` for supported public surface.
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## Workspace Layout
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- `nesemu`: reusable emulation library and host-facing runtime wrappers
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- `crates/nesemu-adapter-api`: backend-agnostic adapter traits
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- `crates/nesemu-adapter-headless`: headless/null adapter implementations
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- `crates/nesemu-desktop`: GTK4 desktop frontend that consumes the root crate
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## High-Level Layers
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The workspace is split into four layers:
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1. `native_core`
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Owns emulation correctness and hardware-facing behavior.
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2. `runtime`
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Wraps the core with host-oriented execution, pacing, lifecycle control, and save-state helpers.
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3. adapter crates
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Define integration edges without coupling the core to a concrete backend.
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4. desktop frontend
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Serves as a consumer and manual test harness, not as part of the library contract.
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## Core Module Boundaries
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- `src/native_core/cpu`: 6502 execution, addressing helpers, opcode dispatch
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- `src/native_core/ppu`: rendering pipeline, VRAM/OAM/register behavior
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- `src/native_core/apu`: timing, channel state, and audio-facing hardware state
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- `src/native_core/bus`: component wiring and device-visible read/write semantics
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- `src/native_core/mapper`: cartridge mapper abstraction and concrete implementations
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- `src/native_core/ines`: iNES parsing and ROM metadata
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- `src/native_core/state_io`: shared state decoding helpers
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## Runtime Module Boundaries
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- `src/runtime/core.rs`: `NesRuntime` orchestration around CPU + bus
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- `src/runtime/state.rs`: runtime save/load state format
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- `src/runtime/audio.rs`: interim PCM synthesis from core state
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- `src/runtime/timing.rs`: frame pacing types and video timing
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- `src/runtime/types.rs`: public joypad-related types and helpers
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- `src/runtime/host/io.rs`: host IO traits and null implementations
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- `src/runtime/host/executor.rs`: per-frame execution unit
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- `src/runtime/host/clock.rs`: clock abstraction and pacing implementations
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- `src/runtime/host/loop_runner.rs`: host loop wrapper for frame-based execution
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- `src/runtime/host/session.rs`: app lifecycle wrapper for running, pausing, and stepping
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## Data Flow
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At a high level, the runtime stack looks like this:
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1. ROM bytes are parsed into cartridge metadata and ROM contents.
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2. A mapper is created from the ROM description.
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3. `NativeBus` wires CPU, PPU, APU, mapper, and input-visible state together.
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4. `Cpu6502` executes against the bus.
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5. `NesRuntime` wraps the core to provide frame-level execution, rendering, and save-state helpers.
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6. `RuntimeHostLoop` and `ClientRuntime` adapt the runtime to host application control flow.
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## Public Surface Strategy
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The root crate re-exports the integration-critical API so external users do not need to depend on the internal module layout.
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The design intent is:
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- external clients use root re-exports and `runtime`
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- advanced clients may use `native_core`
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- internal module paths are free to evolve faster than the root surface
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## Host Responsibilities
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The library intentionally leaves these concerns to the host application:
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- windowing and presentation backend
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- audio device/output backend
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- platform input mapping
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- ROM file I/O
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- persistent state storage
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## Input, Video, and Audio Contracts
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- `JoypadButtons` are exposed in the public order `[Up, Down, Left, Right, A, B, Start, Select]`
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- `InputProvider` polls the current button state from the host
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- `VideoOutput` receives RGBA frames
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- `AudioOutput` receives mixed mono samples
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- port 2 is currently treated as disconnected in the exposed core API
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## Save-State Design
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- `NativeBus::save_state` and `NativeBus::load_state` persist low-level emulator state
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- `NesRuntime` extends that state with runtime metadata such as frame number and active buttons
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- save-state payloads are versioned for crate-internal use, not for long-term external compatibility
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## Testing Layout
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- CPU tests are grouped by behavior, interrupts, and invariants
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- mapper tests are grouped by mapper family and property-style checks
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- runtime tests cover frame execution, pacing, state roundtrips, and lifecycle control
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- `tests/public_api.rs` exercises the supported public flow as a black-box consumer
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## Constraints And Tradeoffs
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- no platform backend is bundled beyond the GTK desktop example
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- audio mixing in `runtime/audio.rs` is intentionally interim
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- optional adapter crates are thin integration layers, not mandatory parts of the core runtime
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- compatibility promises are defined in `docs/api_contract.md`, not by internal module visibility
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