0xrsydn/gameboy-rust
1
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

feat(memory): add region-dependent Thumb open-bus snapshots

Browse source 
Repeat the mapped PC+4 halfword for Thumb code in EWRAM, palette RAM, VRAM, and ROM. Use the aligned PC+4 word for BIOS/OAM. Keep retained BIOS history separate from current unused-memory reads. Reuse one instruction snapshot without extra data cycles or host/fetch/DMA fallbacks.

Keep IWRAM and 16 MiB region-crossing fetches diagnostic until prior bus history is modeled. Add original regressions for regions, alignments, mirrors, physical wrap, signed and unaligned loads, block/stack/PC loads, aliases, modes, short ROMs, strict errors, BIOS isolation, and nominal device progression. Record documented rules and remaining limits.

Darwin arm64 validation: 890 workspace tests and 821 core/demo tests in each of debug and release; 39 preparation tests; native ROM windows in both profiles; ten window/graphics smoke modes; fmt, clippy, and rustdoc. Public ARM, Thumb, memory, and BIOS reports remain identical to previous passing results and between profiles. No physical-hardware or independent public Thumb open-bus conformance claim.
This commit is contained in:
0xrsydn 2026-10-06 01:25:41 +07:00
commit 8360ba4652
11 changed files with 528 additions and 36 deletions
Download patch file Download diff file Expand all files Collapse all files

4
docs/references.md
View file

@ -50,8 +50,8 @@ Hardware references used for the core:
- [NanoBoyAdvance keypad implementation](https://github.com/nba-emu/NanoBoyAdvance/blob/master/src/nba/src/hw/keypad/keypad.cc), compared for control access widths; its AND/retrigger behavior differs from the chosen polling model.
- [mGBA keypad timing issue](https://github.com/mgba-emu/mgba/issues/2490), for frontend frame-based input timing limits.
- [Tonc hardware interrupts](https://gbadev.net/tonc/interrupts.html), for keypad source enable and IF/IE bit 12.
- [GBATEK memory mirrors, video byte writes, and unused-memory reads](https://problemkaputt.de/gbatek-gba-unpredictable-things.htm), for unused address ranges, ARM PC+8 open bus, byte lanes, the distinct Thumb region/history rules, and PC-dependent BIOS read protection.
- [nocash GBA open-bus discussion](https://www.ngemu.com/threads/gba-open-bus.170809/), for the distinction between ARM prefetch and region-dependent Thumb values.
- [GBATEK memory mirrors, video byte writes, and unused-memory reads](https://problemkaputt.de/gbatek-gba-unpredictable-things.htm), for unused address ranges, ARM PC+8 open bus, byte lanes, the distinct Thumb region/history rules, and PC-dependent BIOS read protection. The Thumb implementation follows its 16-bit-region and BIOS/OAM formulas; IWRAM and region-transition history remain unsupported.
- [nocash GBA open-bus discussion](https://www.ngemu.com/threads/gba-open-bus.170809/), for ARM prefetch, repeated Thumb halfwords in 16-bit regions, aligned BIOS/OAM words, and history-dependent IWRAM lanes. Its data-load overwrite note prevents treating P+2 as a universal IWRAM rule.
- [mGBA memory implementation](https://github.com/mgba-emu/mgba/blob/master/src/gba/memory.c), reviewed for `GBALoadBad`, ARM prefetch sourcing, byte/halfword lane selection, and separate DMA/history behavior. Also reviewed its BIOS region-exit prefetch retention and protected-load lane selection.
- [GBATEK GBA memory map and bus widths](https://problemkaputt.de/gbatek-gba-memory-map.htm).
- [GBATEK GBA DMA transfers](https://problemkaputt.de/gbatek-gba-dma-transfers.htm).