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Digimon World 2 Decompilation

A matching decompilation of Digimon World 2 for the Sony PlayStation.

The goal is to recover readable C that, when compiled with a period-correct toolchain, produces a binary byte-identical to the original executable, then a moddable full-source tree.

Item	Value
Platform	PlayStation (PSX / PS1)
Target	USA main executable SLUS_011.93 + 7 stage overlays
Disc (USA)	SLUS-01193
Exe SHA-1	e55ed5bf354def07f0cbf4e1fb7fb5f99204f220 (651264 bytes)
Overlays	STAG0000/1000/1100/2000/3000/3500/4000.PRO, loaded at 0x80063360
Compiler	GCC 2.8.1 (PSX cc1) + maspsx
Structure	main exe + 7 stage overlays (AAA/3.PRO/STAG*.PRO)
License (project code)	CC0 1.0

You must own the game. This repository contains no ROMs, disc images, or copyrighted assets. rom/ assets/ build/ are made from your own disc and are gitignored. Obtain a legal dump of your own disc.

asm/ and linkers/ are splat output. They are still committed today so the progress CI can build without a disc. That covers only the PsyQ library asm (code and data); the game's data in the exe and the overlays is C. Opaque content inside C units (bitmaps, CLUTs, tables such as the CD file table, a few padding bytes) is copied from your disc at build time (configs/USA/include_bin.txt, configs/USA/image_bytes.txt). They will move out of the repo (see issue #6).

Status

All 1088 game functions are matched C. The C rebuilds the retail executable and all 7 stage overlays byte-identical.

Naming is done. Functions, globals and struct fields have real names where the code proves them. A few keep their func_ / D_ names on purpose (empty stubs, unreferenced filler words). The source is split into one file per module, along the retail file boundaries (src/main/sys.c, src/main/savedata.c, src/stag3000/battle.c, src/stag4000/floor.c ...).

Every global has one layout and a documented owner: doc/STATE_MAP.md lists each global of the exe and the overlays as player, world, engine, constant or debug state, with its writers and readers, the memory map and the game mode to overlay table.

The build is shiftable, and that is the modding build. No code or data holds a fixed address: every pointer is a symbol, and the exe and the overlays link against each other by name. python3 tools/build_dw2.py --shift-test pads main and STAG1000.PRO so every address moves, and that image boots. So you can change the C, add code or data and relink; the SHA-1 check then no longer applies. The one fixed limit on growth: the heap starts at 0x80075000 (Mem_HeapStart), right after the largest overlay (STAG3000.PRO), so move it if main and that overlay together grow by more than 0xF5C bytes.

The last two functions:

• Task_Run (the task scheduler) runs every update and draw callback on a stack in the scratchpad RAM. C cannot move the stack pointer, so the switch is two small __asm__ statements around the calls, the rest is plain C. The original most likely did the same.
• stag4000:func_8006D418 returns the same field on both sides of a flag test. The test does nothing, but GCC 2.8.1 only merges the two arms after register allocation, and retail's code has exactly that allocation. No form without the test produces it.

A function counts as matched only when its C reproduces the retail bytes with the compiler setup of its translation unit and no asm rewrites: GCC 2.8.1-psx -O2, main game -G8 with maspsx --aspsx-version=2.81, overlays -G0 with 2.77, plus a few per-unit flags in tools/build_dw2.py. Functions that still need a per-function flag set or asm rewrites are listed separately and are not counted. PsyQ library code (PsyQ 4.7 in the exe, libpress 4.6 in STAG1000.PRO) is not game code and is excluded from progress (configs/USA/psyq_funcs.txt). Counts come from tools/strict_report.py, which builds each function with and without the post-processing and compares it against the target. See issue #5.

Progress by component

Component	Functions	Matched	Progress	Flags per function	Asm rewrites	Asm
Main executable (SLUS_011.93, game code)	368	368	▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰ 100.00%	0	0	0
Stage overlays (AAA/3.PRO)	720	720	▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰ 100.00%	0	0	0
└ STAG0000.PRO	69	69	▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰ 100.00%	0	0	0
└ STAG1000.PRO	17	17	▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰ 100.00%	0	0	0
└ STAG1100.PRO	55	55	▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰ 100.00%	0	0	0
└ STAG2000.PRO	133	133	▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰ 100.00%	0	0	0
└ STAG3000.PRO	123	123	▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰ 100.00%	0	0	0
└ STAG3500.PRO	108	108	▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰ 100.00%	0	0	0
└ STAG4000.PRO	215	215	▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰ 100.00%	0	0	0
Total (game code)	1088	1088	▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰▰ 100.00%	0	0	0
PsyQ libraries (not counted)	558

DW2 has the main exe plus 7 stage overlays on the disc, AAA/3.PRO/STAG0000.PRO to STAG4000.PRO. The main exe loads one at a time to 0x80063360 (func_80013308, indexed by the game mode), so they share one address range. Each overlay is split into its own unit (src/stagXXXX, asm/USA/stagXXXX) and relinks byte-identical to the retail file.

The AAA directory is left out of the disc's root directory record, so a plain ISO extract only shows SLUS_011.93 and SYSTEM.CNF. dumpsxiso -pt (path table walk) extracts the full tree.

PsyQ library code stays as split asm, as in other PS1 decomps. The crt0 startup is the PsyQ SNMAIN hand asm.

Layout

Path	What
src/ / include/	decompiled C and headers
configs/	splat config + symbol maps
doc/	STATE_MAP.md: global state map, memory map, scene table
tools/	gcc-psx, maspsx, m2c, decomp-permuter, asm-differ, mkpsxiso, build scripts

Quick start

Supply your own Digimon World 2 (SLUS-01193) disc and extract it with dumpsxiso -pt to dumps/disc/ (SLUS_011.93 plus AAA/3.PRO/STAG*.PRO). Then:

python3 -m venv venv                                # venv\Scripts on Windows
pip install -r requirements.txt
python3 -m splat split configs/USA/SLUS_011.93.yaml # regenerate asm/ and linkers/
python3 -m splat split configs/USA/stag1000.yaml    # same for each stagXXXX.yaml
python3 tools/build_dw2.py                          # expect: SLUS_011.93: OK + 7x STAGxxxx.PRO: OK

tools/build_dw2.py preprocesses and compiles src/**/*.c through the PSX cc1 + maspsx pipeline, assembles the remaining split asm, links with the splat linker script plus the auto-detected hardware and kernel symbols, then checks the SHA-1 against your disc's exe. build/USA/out/SLUS_011.93: OK means the whole exe still reproduces byte-for-byte. Each overlay is then linked with its own script and checked the same way (build/USA/out/STAGxxxx.PRO: OK); --overlays-only builds just the overlays.

Contributing names

1. python3 tools/rename.py func_XXXXXXXX Module_VerbNoun renames a main exe function or global everywhere (--unit stagXXXX for an overlay, --batch file for many). python3 tools/rename_field.py --batch file renames struct fields with the compiler as the checker.
2. Only name what the code proves. A wrong name is worse than func_.
3. Verify with python3 tools/build_dw2.py. Only OK for every file counts as done.

Credits

Workflow and toolchain derived from the Parasite Eve 2 decomp. DW2 file-format documentation by RmBeastbow. Thanks to ThirstyWraith for pointing out the stage overlays (issue #3) and for their STAG3000 battle notes and decomp.me scratches (issue #4), which seeded the matches of the battle status and item functions.