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fix(bios): return cleanly for empty LZ77 streams

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0xrsydn 2026-10-07 09:05:45 +07:00
commit 7772a9d8eb
8 changed files with 156 additions and 11 deletions
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@ -87,6 +87,7 @@ Update this file when a feature lands or a limit is removed.
- Raw ROM-file loading with original BIOS boot, terminal diagnostics, and final CPU/step reports.
- Firmware boot initializes BG2/BG3 identity scales for bitmap and affine programs that do not program their own matrices.
- RegisterRamReset supports disabled sound and disconnected serial initialization, including the common `r0=0xff` request.
- Both LZ77 BIOS services return without output for zero-length headers, including all-zero headers; nonempty validation remains strict.
- Disconnected Joybus selection, local data/status registers, and transmit-pending state without invented remote events or IRQs.
- Direct Sound A/B support timer-driven FIFO playback, stereo digital levels, and DMA1/A or DMA2/B refill blocks.
- PSG pulse channels 1 and 2 support independent nominal frequency/duty playback, length, envelope, status, and stereo mixing. Channel 1 also supports sweep.
@ -192,6 +193,9 @@ A later [fixed-time input probe](research/emerald-wave.md) found a wave trigger
Wave support now passes that point and reaches 1,320 frames with scheduled Start/A presses and releases.
Output differs from a no-input control, but readable menus and gameplay remain unverified.
Flash writing and host persistence now pass original save/restart/load tests. Emerald saving and reloading remain unverified.
A user reached starter selection, then reported a BIOS invalid-argument trap.
An [isolated reproduction](research/emerald-empty-lz.md) identified a zero-length LZ77 header rejected before the length check.
The replacement BIOS now returns for that empty stream. Full starter-selection progress after this correction needs user retesting.
Without `--rtc`, cartridge GPIO writes still return read-only diagnostics.
No title-screen, gameplay, or audible-game compatibility is established.
See [the startup result](research/emerald-reset.md) for the bounded run and next investigation.