A new year and a new XGS

Well, it took a lot longer than I thought, but I’ve finally managed to roll out my first alpha prerelease of the XGS rewrite. At the moment only text mode is implemented, and the boot sequence does not yet complete properly, but it dos start up. Since this is at such an early stage of development I am not making this available as a tarball release. Those interested in playing with it can download it directly from the GitHub page.


Changes in this Version

The entire code base has been converted from C to C++, and heavily refactored so that the individual code modules correspond more closely to the individual pieces of the IIGS’s hardware.

All of the platform-specific drivers have been removed; instead, the code uses SDL2 for most platform-specific functions.

The emulation timing has been rewritten to use Linux timer FDs. This is currently the dependency that makes the code non-portable.

The CPU emulation has been completely rewritten. The new version is significantly easier to understand and debug than the old version, as all of the cryptic and convoluted C macros are gone. The opcode execution logic is now implemented in a C++ template which is used to generates individual classes optimized for specific combinations of memory and index width.

What’s Next

At the moment all of my energy is focused on fixing whatever issue or issues are causing the boot sequence to crash. This involves running both old and new XGS in debug mode and comparing the resulting execution traces.

Once the boot issue is fixed the keyboard handling needs a lot of love. The current implementation is only partially usable, especially since it fails to properly handle applying modifiers (shift & control) to key presses before putting them into the input buffer. As a result you can’t even type many characters, making it difficult to investigate problems and run tests within the emulation.