86 lines
4.1 KiB
Markdown
86 lines
4.1 KiB
Markdown
# Local Emerald visible-progress probe
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## Method
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A temporary host driver uses public core APIs (deleted after use; lives
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outside version control). It boots the local user-supplied ROM with
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`bios::boot`, selects `CartridgeHardware::Rtc` and `SaveDevice::Flash128`,
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fixes the RTC to `[24, 1, 1, 1, 12, 0, 0]` without advancing it, enables
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scanline rendering, and calls `Machine::run_until_vblank(400000)` once per
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frame. Input snapshots apply after each VBlank capture, before the next
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machine step. Frames dump as checksums plus a final PPM for visual reading.
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No ROM bytes, screenshots, or extracted code are committed.
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Three schedules were used:
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- No input (attract mode).
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- `advance`: periodic A/Start taps (A for 10 of every 120 frames, Start for
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10 of every 120 frames offset by 60) to walk through title, menu, and
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dialogue.
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- `sweep`: deterministic rotation holding each button 20 frames in turn.
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## Observed visible progress
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No-input attract mode renders the title screen, the Pokémon logo, the
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NEW GAME / OPTION menu, the Prof. Birch scene, and legible dialogue text
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(`Hi! Sorry to keep yo`, `Welcome to the world of POKéMON!`). Menu and
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dialogue text, the Birch sprite, and the spotlight composite correctly.
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The `advance` schedule reaches further: Birch dialogue, the `And are you?`
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gender prompt, and — at 12,000 frames — the in-game start menu (`BAG A SAVE
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OPTION EXIT`) over the overworld with the player sprite in a room. Frame
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checksums evolve continuously through the run; PC samples alternate between
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the `0x080008c6–0x080008cc` wait loop and game code (`0x082e6dcc`,
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`0x082e6dce`).
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The `sweep` schedule changes captured output per input (input-dependent
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execution) but its denser presses stall the intro on a blue field; raw
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button rotation is worse than sparse taps for menu progress.
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A 40,000-frame `advance` run is in progress to check the user's reported
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starter-selection trap point (37,101 captured frames in their manual run)
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against the empty-LZ77 correction. Blind taps take a different menu path
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than manual play, so reaching the identical scene is not guaranteed; a
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diagnostic-free run still validates forward progress, while any trap gets
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recorded with full CPU state.
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## Result status
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Execution is diagnostic-free through 12,000 tapped frames (about 1.18
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billion machine steps). This establishes visible menus, sprite/dialogue
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composition, and input-driven progress — not correct gameplay, audio, or
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saving. The old `INVALID_ARGUMENT_TRAP` at starter selection has not yet
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been re-encountered because the probe has not reached that scene.
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## Second-game data point
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A local FireRed ROM (16 MiB) faults during boot init, after about 1.19
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million steps with `--rtc --save-type flash128`:
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```text
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PC=0x081e37d2 CPSR=0x0000003f System/Thumb
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r0=0x09fe2ffe r1=0x00000020
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read-only memory at 0x09fe2ffe
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```
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A dynamic trace shows boot code spilling `0x09fe20f8`, `0x04000204`
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(WAITCNT), and `0x09fe2ffe` to the stack, writing `0x1800` to WAITCNT, then
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`STRH r1,[r0]` of `0x20` to `0x09fe2ffe`. That address is ROM window
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`0x09` past the 16 MiB EOF; the bus reports `ReadOnly`. On hardware the
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`0x09` window mirrors `0x08` and ROM writes are ignored. The following
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instruction stream also loads halfwords from `0x09fe20f8`, so reads past
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EOF would fault next under the current policy. Without `--save-type` the
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same ROM faults earlier at `0x0e005555` (`unmapped memory`), i.e. it also
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expects Flash save hardware. Both failures are recorded, not fixed: mirror
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folding plus write-ignore semantics need independent hardware evidence and
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a deliberate policy decision against the explicit-error convention. See
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[the usability roadmap](../usability-roadmap.md) for sequencing.
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## References
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- [GBATEK memory map](https://problemkaputt.de/gbatek-gba-memory-map.htm):
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three 32 MiB ROM windows at `0x08`/`0x0a`/`0x0c` with wait states 0–2.
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- [mGBA memory at c30aaa8f](https://github.com/mgba-emu/mgba/blob/c30aaa8f/src/gba/memory.c):
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out-of-bounds ROM loads log a game error and return `(address >> 1) &
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0xFFFF`; ROM stores go through patch infrastructure. Precedent for
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non-fatal handling, not a hardware measurement. Not copied.
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