0xrsydn/gameboy-rust
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fix(bios): preserve documented protected-read words at firmware exits

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Place skipped compatibility data at boot, SoftReset, SWI, and IRQ exit PC+8 locations. Preserve the real IRQ callback return instruction as its readback word. Keep CPU and memory behavior image-derived, including caller-supplied images.

Add original boundary, load-lane, caller-state, wait, supplied-image, and builder-fixup regressions. Document the historical failures, research decision, passing public BIOS checkpoint, and remaining fetch-history limits.

Validated on Darwin arm64: 868 workspace tests in debug and release; 799 core/demo tests separately in both profiles; 39 preparation tests; native ROM window tests in both profiles; ten graphics/window smoke modes; fmt, clippy, and rustdoc. Hash-verified public ARM, Thumb, memory, and BIOS suites pass unchanged with identical debug/release reports. BIOS: r12=0, 17606 steps, 197456 nominal cycles, one IRQ entry.
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0xrsydn 2026-10-06 00:37:20 +07:00
commit efdc288db6
15 changed files with 387 additions and 34 deletions
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docs/architecture.md
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@ -125,6 +125,7 @@ The repository is a Cargo workspace with three crates:
| `crates/gba-core/tests/bios/stop.rs` | ARM/Thumb Stop calls, caller preservation, keypad wake, and stopped frame running |
| `crates/gba-core/tests/halt.rs` | HALT wake masks, idle timing, BIOS-only power writes, DMA progress, and validation |
| `crates/gba-core/tests/bios.rs` | ARM/Thumb service calls, copy/fill boundaries, wait races, callback contracts, and boot |
| `crates/gba-core/tests/bios/readback.rs` | Image-derived boot/reset/SWI/IRQ compatibility words, load lanes, caller state, and supplied-image isolation |
| `crates/gba-core/tests/bios/ram_reset.rs` | Selective RAM boundaries, flag combinations, I/O reset, display rendering, DMA/timer latches, and diagnostics |
| `crates/gba-core/tests/bios/reset.rs` | All restart flags, exact RAM boundaries, CPU banks, restart execution, device continuity, and IRQ masking |
| `crates/gba-core/tests/bios/arithmetic.rs` | Arithmetic boundaries, wide-integer references, status restoration, and zero-division diagnostics |