54 lines
2.8 KiB
Markdown
54 lines
2.8 KiB
Markdown
# Local Emerald startup: device reset
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## Initial failure
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A user-supplied local Emerald ROM stopped in the original BIOS replacement during `RegisterRamReset(0xff)`.
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The BIOS deliberately rejected serial/sound flags and executed `INVALID_ARGUMENT_TRAP` (`0xe7f000f1`).
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This was an unsupported service argument, not an ARM instruction-decoder failure.
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No ROM bytes, extracted code, or assets were added to the repository.
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## General correction
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The core now provides a bounded [disabled sound](../hardware/audio.md) and [disconnected serial](../hardware/serial.md) initialization model.
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The BIOS performs reset through original ARM stores against that model.
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Bit 5 selects general-purpose input pins and clears supported serial reset registers.
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Bit 6 disables sound, clears mixing configuration and accessible wave RAM, and sets the functional bias default.
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The low halfword of SIODATA32 is cleared unconditionally, matching the documented BIOS side effect.
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This is not a game-specific bypass. Original ARM and Thumb callers exercise selected flags and the all-device request.
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Tests verify caller preservation, RAM selection, unselected device state, readback masks, and rejected device activity.
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Byte, halfword, word, block-store, and DMA validation retain explicit errors without partial register writes.
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## Reproduction and current result
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Use a local ROM that you may lawfully use:
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```sh
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direnv exec . cargo run --locked --release -- --rom roms/pokemon-emerald.gba --steps 1000000
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direnv exec . cargo run --locked --release -- --rom roms/pokemon-emerald.gba --window --frames 120
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```
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Both runs now pass the BIOS reset and stop at the game's sound activation write:
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```text
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PC=0x082e0518
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unsupported sound master enable (audio engine not implemented): write 0x8f at 0x04000084
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```
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The native run captures startup frames before this diagnostic. These are not evidence of a working title screen or gameplay.
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The window run does not reach its requested frame limit and correctly exits with failure.
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Terminal execution is also diagnostic, not a compatibility pass.
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Results apply to this local file; no cartridge revision or checksum was inferred from its filename.
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## Validation and next requirement
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Workspace debug/release tests, strict Clippy, public ARM/Thumb/memory/BIOS checkpoints, and pinned Pong scenarios pass.
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Native ROM-window tests and graphics smoke modes pass on Darwin arm64.
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The pinned Pong debug/release reports match.
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The next observed startup requirement is active audio-device behavior, starting at SOUNDCNT_X master enable.
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Implement channel/FIFO clocks, state, DMA requests, and an output interface before claiming sound support.
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Do not make enable succeed solely to suppress this diagnostic.
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Cartridge saves remain a separate required feature. SRAM alone will not support Emerald's Flash save protocol.
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Hardware and emulator references are recorded in the linked subsystem documents.
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