Disassembly and analysis of SubLOGIC's Flight Simulator II (FS2) for the Apple II platform, circa 1984.

Two halves:

1. Disassembly of the original 6502 binary under src/ (chunks chunk2.s .. chunk5.s). make validate enforces byte-identity against the original FS2 chunks.
2. C port in port/ (SDL2). A from-scratch reimplementation that boots into the Meigs Field scenery, flies the FS2 flight model, renders scenery via a faithful translation of chunk5's bytecode VM, and adds modern affordances (config menu, in-flight editor, joystick, audio). See port/PORT_STATUS.md for the per-feature comparison and ARCHITECTURE.md for the design notes.

Disassembly

The target is @qkumba's ProDOS port of FS2, which has a custom loader which decompressess chunks of code/data into memory. The project primarily focuses on understanding those chunks, which represent the memory-resident code of the original FS2.

The cc65 tool chain is used; source files target the ca65 macro assembler; ca65 and ld65 must be available. Build via make and use make validate to verify that the built chunks (out/?_????-????) are byte-identical to the original chunks (orig/?_????-????).

PRs welcome. Comments are strongly encouraged. Macro use for common patterns is also encouraged, where it helps understanding the original code.

Loader

The source for @qkumba's ProDOS loader is included. To build the binary, use make binary. The output will be out/fs2#062499. This requires the following addtional tools to be available on the command line.

• apultra - https://github.com/emmanuel-marty/apultra (compression)
• acme - https://sourceforge.net/projects/acme-crossass/ (cross-assembler)

Note that the binary on its own is insufficient to actually run FS2; an adjacent file representing a full image of the 140k FS2 disk is required, which includes the dynamically loaded scenery database. This file (and more) are present on the orig/flight simulator 2 with scenery PRODOS (san inc pack).po. If you do build the binary, you can transfer it to a copy of that disk image and BRUN it.

Additionally, a out/loader.system#ff2000 file will also be produced. This can be transferred to a disk as a SYS file and executed to load/run the FS2 binary.