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Windows ROM development build - Flash saves and hot reload (2026-09-24)

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@maxiwamoto maxiwamoto released this 24 Sep 04:14
rom-dev-2026.09.24
9806b70

Windows download

Download openmsx-rom-dev-2026.09.24-windows-x64.zip, extract it completely into a writable folder, and run Start-openMSX.cmd. Windows 10/11 x64. No installation is required.

The launcher keeps settings and saves in profile/ beside the executable, separate from your normal openMSX installation. C-BIOS and the required runtime DLLs are included. Supply your own commercial machine firmware and game ROMs. Do not share this experimental profile with older openMSX builds.

Included features

  • Flash saves survive ROM updates: preserve sectors programmed/erased by the game and reload untouched sectors from the current ROM. Games must store saves separately from code/assets at erase-sector boundaries. This supports games that already implement Flash saving.
  • Replace an inserted ROM on Windows: rebuild or replace the host file while the running emulator keeps its existing snapshot.
  • Ctrl+Shift+R: reload the ROM from disk and reset.
  • Alt+F8, then Ctrl+Shift+F7: save a test point and restore it using updated ROM assets. Save before asset unpacking; RAM/code/bank layouts must remain compatible. Game-written Flash comes from the saved state.

Normal reset and normal state loading retain their existing behavior. Legacy full-chip saves remain supported conservatively and can still mask newer ROM contents. Keep your existing saves backed up; no automatic save-only sector migration is guessed.

Status and validation

This is an experimental fork build, not an official openMSX release. The sparse Flash format is still proposed upstream. Credit to Laurens Holst (Grauw) for the sector-persistence design in draft openMSX#1629.

The updated code addresses the reported portability, exception-safety and test-harness findings. Local Windows x64 validation passed 30 Flash sessions (including legacy files and v4 states), four ROM replacement cases, three reload/reset cases, four developer-restore cases and three harness boundary tests. The extracted package also passed a C-BIOS startup test in a path containing spaces, with isolated-profile and shortcut checks. Updated upstream CI awaits maintainer approval; no claim of a new upstream scan pass is made. Other platforms and Flash cartridge families need more testing.

Files

  • windows-x64.zip: ready-to-run emulator, launcher, documentation, licenses and C-BIOS.
  • source.zip: matching project source, build recipes/patches and original third-party dependency archives; not required to play.
  • SHA256SUMS.txt: SHA-256 checksums for both ZIP files.

BUILD.json inside the Windows ZIP records the exact source commit and executable/DLL hashes. Built with MSVC v145, x64 Release, source commit 9806b70975c68d945a02f334bebb6bc54789cae6. The executable is unsigned.

See START-HERE.md in the package and the fork README for setup and compatibility details.

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