77 lines
5.2 KiB
Markdown
77 lines
5.2 KiB
Markdown
# General GBA usability roadmap
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The goal is a general-purpose GBA emulator, not a port of one game.
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Pokémon Emerald is one possible future compatibility target. It does not define hardware behavior.
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Nintendo DS support remains a separate phase.
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## Usability criteria
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A usable release must demonstrate these results with several lawfully obtained games:
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- Boot into a menu and enter gameplay without an unsupported-hardware diagnostic.
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- Present stable graphics in the native Darwin window.
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- Respond to button presses, held buttons, and releases.
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- Preserve supported cartridge saves across process restarts without damaging existing files.
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- Produce audio through an isolated host output layer.
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- Exit cleanly and report unsupported behavior clearly.
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A bounded run without a diagnostic is not proof of playability.
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A test pass establishes only the configured assertions, not complete game compatibility.
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## Work order
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1. Establish repeatable gameplay checks using licensed public homebrew.
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Add VBlank completion, button schedules, and captured-pixel assertions to the ROM suite runner.
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2. Exercise menus and gameplay in the native window. Record the exact ROM revision and checksums.
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3. Select another independent program. Fix demonstrated boot, graphics, or input failures with original regressions.
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4. Implement cartridge save devices and safe host persistence. Verify saving and reloading across processes.
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5. Implement audio devices and host output. Keep host dependencies outside `gba-core`.
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6. Expand the compatibility matrix across games and hardware features.
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Refine timing when independent tests or gameplay failures show a requirement.
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SRAM, Flash, and EEPROM require different protocols. Supporting one does not establish support for the others.
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Audio needs device clocks, mixing, and buffering; accepting sound-register writes alone is not audio support.
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The detailed hardware limits remain in [status.md](status.md).
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## Current gameplay baseline
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The [pinned Pong homebrew](public-pong.md) passes scripted menus, ball movement, and paddle press/release checks.
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The native Darwin window also starts and presents frames without a diagnostic.
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This exposed and corrected missing firmware affine-scale initialization, without a game-specific patch.
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Frame-based scenarios and the preparation adapter now make the result repeatable.
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A local Emerald run now passes its initial all-device reset, master sound enable, and pulse/noise triggers.
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It also passes normal serial transfers and idle multiplayer configuration.
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With `--rtc --save-type flash128`, it passes Game Pak GPIO setup, RTC reads, and Flash identification.
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It next stops at Joybus serial-mode selection.
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The core has tested Direct Sound, both pulse channels, and noise channel 4.
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Wave channel 3, a continuous sample stream, and desktop audio output remain missing.
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See [the runtime result](research/emerald-reset.md). Disconnected Joybus configuration is the next demonstrated startup requirement.
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The separate save requirement includes Flash programming/erase and safe host persistence. Identification/read support is not successful saving.
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SRAM is byte-addressable battery-backed save memory. Flash and EEPROM remain separate protocols.
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[Paperdomo101/2048-GBA at ae36800d](https://github.com/Paperdomo101/2048-GBA/tree/ae36800dfa1314f96c4c8785b5c2d077fb731aff) is the next independent candidate.
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Its CC0 source calls `load_state()` before audio initialization and reads/writes `sram_mem` one byte at a time.
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It also uses Maxmod audio, so SRAM alone will not establish compatibility.
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This candidate has not been run: the pinned tree has no ROM, GitHub has no release asset, and the linked download returned HTTP 522.
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A reproducible source build or an accessible upstream ROM is needed before recording a runtime result.
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Next implementation steps:
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1. Research the demonstrated Joybus configuration failure without inventing a connected device.
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2. Extend explicit Flash selection with verified programming, erase, and busy behavior. Keep absent devices and unsupported commands diagnostic.
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Add SRAM separately when the independent candidate requires it; verify its widths, mirroring, and wait behavior first.
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3. Add bounded save loading and safe persistence in the desktop crate. Do not put file operations in the core.
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4. Test a save/restart/load cycle across processes with original ROM instructions before external-game validation.
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5. Resume the second-game run and implement demonstrated audio requirements rather than accepting writes without behavior.
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## Development loop
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For each feature, inspect the source and hardware evidence, then write original regression tests.
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Implement the smallest general behavior that satisfies the requirement.
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Run focused tests, workspace validation, and relevant native-window checks through `direnv exec .`.
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Update behavior notes and compatibility evidence. Save a semantic jj change with its own bookmark.
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Then select the next demonstrated requirement without waiting for another confirmation.
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Stop for missing access, a necessary product decision, or a destructive operation that needs approval.
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Do not replace unsupported hardware with game-specific patches or silent register stubs.
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Keep external ROMs, firmware, implementation source, and assets outside version control.
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