3.6 KiB
Local Emerald startup: device reset
Initial failure
A user-supplied local Emerald ROM stopped in the original BIOS replacement during RegisterRamReset(0xff).
The BIOS deliberately rejected serial/sound flags and executed INVALID_ARGUMENT_TRAP (0xe7f000f1).
This was an unsupported service argument, not an ARM instruction-decoder failure.
No ROM bytes, extracted code, or assets were added to the repository.
General correction
The reset correction introduced bounded sound and disconnected serial initialization models. The sound model now also supports Direct Sound, bounded FIFO DMA, and nominal pulse channel 1 playback. The BIOS performs reset through original ARM stores against that model. Bit 5 selects general-purpose input pins and clears supported serial reset registers. Bit 6 disables sound, resets FIFO queues, clears mixing configuration and accessible wave RAM, and sets the functional bias default. The low halfword of SIODATA32 is cleared unconditionally, matching the documented BIOS side effect.
This is not a game-specific bypass. Original ARM and Thumb callers exercise selected flags and the all-device request. Tests verify caller preservation, RAM selection, unselected device state, readback masks, and rejected device activity. Byte, halfword, word, block-store, and DMA validation retain explicit errors without partial register writes.
Reproduction and current result
Use a local ROM that you may lawfully use:
direnv exec . cargo run --locked --release -- --rom roms/pokemon-emerald.gba --steps 1000000
direnv exec . cargo run --locked --release -- --rom roms/pokemon-emerald.gba --window --frames 120
The earlier reset-only implementation stopped at master sound enable (0x04000084, PC 0x082e0518).
The Direct Sound increment then reached a PSG channel 1 trigger (0x04000065, PC 0x082e03bc).
After implementing channel 1, both runs pass that trigger and stop at channel 2:
Steps: 321161; instructions: 320649; IRQ entries: 0; DMA units: 512; HALT idle: 0
Nominal cycles: 1038742
PC=0x082e03c0
unsupported PSG channel trigger (synthesis not implemented): write 0x80 at 0x0400006d
The native run captures three startup frames. Audio-device behavior is validated by original tests, not by audible game output.
The native run captures startup frames before this diagnostic. These are not evidence of a working title screen or gameplay. The window run does not reach its requested frame limit and correctly exits with failure. Terminal execution is also diagnostic, not a compatibility pass. Results apply to this local file; no cartridge revision or checksum was inferred from its filename.
Validation and next requirement
Workspace debug/release tests, strict Clippy, public ARM/Thumb/memory/BIOS checkpoints, and pinned Pong scenarios pass. Native ROM-window tests and graphics smoke modes pass on Darwin arm64. The pinned Pong debug/release reports match.
The next observed startup requirement is PSG pulse channel 2, which has no sweep unit. Channel 1 now has nominal waveform, length, envelope, sweep, and stereo mixing behavior. Direct Sound has FIFO clocks and nominal DMA requests. Both use the instantaneous digital-level inspection interface. A continuous sample stream and desktop output are still missing. Do not treat digital-level tests as audible-game validation. Do not suppress the PSG trigger diagnostic without implementing the requested device behavior. Cartridge saves remain a separate required feature. SRAM alone will not support Emerald's Flash save protocol.
Hardware and emulator references are recorded in the linked subsystem documents.