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

feat(memory): retain aligned Thumb BIOS prefetch words

Browse source 
Snapshot the full word at (executing PC+4)&~3 for Thumb BIOS execution, using strict image reads and incoming instruction state. Keep ARM PC+8 open bus separate and unchanged. Commit snapshots only after successful steps; preserve diagnostic behavior for unavailable lookahead.

Add original regression coverage for both code alignments, load widths and lanes, signed and unaligned values, processor modes, sequential fetches, ARM/Thumb transitions, SWI, RAM-backed POP exits, BIOS boundaries, failure retention, and nominal device progression. Record source evidence and explicit pipeline/hardware-validation limits.

Darwin arm64 validation: 878 workspace tests and 809 core/demo tests in each of debug and release; 39 Python tests; native ROM window tests in both profiles; ten window/graphics smoke modes; fmt, clippy, and rustdoc. Public ARM, Thumb, memory, and BIOS reports match prior passing reports and match between profiles. No physical-hardware validation claimed.
This commit is contained in:
0xrsydn 2026-10-06 00:57:49 +07:00
commit cb4670c245
12 changed files with 427 additions and 25 deletions
Download patch file Download diff file Expand all files Collapse all files

3
docs/research/bios-readback.md
View file

@ -93,6 +93,7 @@ Workspace tests, preparation tests, lint checks, rustdoc, native ROM windows, an
- Keep synthetic caller-supplied images image-derived, including images with different exit words.
- Rerun public ARM, Thumb, and memory suites and native Darwin regressions.
This change does not implement a persistent instruction pipeline, Thumb BIOS fetch history, or exact firmware timing.
The firmware-layout fix did not implement a persistent instruction pipeline, Thumb BIOS fetch history, or exact firmware timing.
A subsequent [Thumb BIOS snapshot change](thumb-bios-prefetch.md) adds bounded aligned-word history, with separate tests and explicit limits.
It does not prove complete BIOS compatibility or commercial-game support.
The public BIOS ROM checks these protected-read values; it is not a comprehensive BIOS service suite.