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ROMCNV - CPS2 ROM Converter

A tool to convert Capcom CPS2 arcade ROMs into an optimized cache format for use with NJEMU emulators on memory-constrained platforms.

Why Convert ROMs?

CPS2 ROMs contain graphics data that may exceed the available RAM on: - PSP: ~24-64MB available RAM - PS2: ~32MB available RAM

This converter processes the ROM files and creates optimized cache files that can be loaded in smaller chunks during emulation.

Supported Platforms

Platform	Executable	Cache Location
Windows	`romcnv_cps2.exe`	`./cache/`
Linux/macOS	`romcnv_cps2`	`./cache/`
Web	Online Converter	Download as ZIP
PSP	N/A (use desktop tool)	`/PSP/GAME/CPS2PSP/cache/`
PS2	N/A (use desktop tool)	`mass:/CPS2PSP/cache/`

Usage

Basic Usage

Convert a single ROM:

romcnv_cps2 /path/to/game.zip

Command Line Options

Option	Description
`-all`	Convert all ROMs in the specified directory
`-raw`	Force raw cache file format (overrides per-game defaults)
`-zip`	Create a ZIP compressed cache file (reduces storage space)
`-folder`	Create a folder with individual block files instead of a single raw cache
`-batch`	Batch mode - don’t pause between conversions

Note: Some games default to ZIP format for historical reasons. Use -raw to explicitly force the single-file .cache format regardless of per-game defaults.

Examples

Convert a single game:

romcnv_cps2 "D:\roms\ssf2.zip"

Convert with ZIP compression:

romcnv_cps2 "D:\roms\avsp.zip" -zip

Convert multiple games in batch mode:

romcnv_cps2 "D:\roms\avsp.zip" -zip -batch
romcnv_cps2 "D:\roms\qndream.zip" -zip -batch
romcnv_cps2 "D:\roms\mvsc.zip" -batch
romcnv_cps2 "D:\roms\vsav.zip"

Convert all ROMs in a directory:

romcnv_cps2 "D:\roms" -all

Convert all ROMs with ZIP compression:

romcnv_cps2 "D:\roms" -all -zip

Convert with folder format:

romcnv_cps2 "D:\roms\avsp.zip" -folder

Linux/macOS Examples

# Convert a single ROM
./romcnv_cps2 /home/user/roms/ssf2.zip

# Convert with ZIP compression
./romcnv_cps2 /home/user/roms/ssf2.zip -zip

# Convert with folder format
./romcnv_cps2 /home/user/roms/ssf2.zip -folder

# Convert all ROMs in directory
./romcnv_cps2 /home/user/roms -all

# Convert all with ZIP compression
./romcnv_cps2 /home/user/roms -all -zip

# Convert all with folder format
./romcnv_cps2 /home/user/roms -all -folder

Output

The converter creates a cache directory containing one of: - gamename.cache — Single raw cache file (default) - gamename_cache.zip — ZIP compressed cache file (with -zip) - gamename_cache/ — Folder with individual block files (with -folder)

All three formats are supported by the emulator on all platforms.

File Structure for Emulators

PSP (raw format — default):

/PSP/GAME/CPS2PSP/
├── roms/
│   └── game.zip
└── cache/
    └── game.cache

PSP (zip format):

/PSP/GAME/CPS2PSP/
├── roms/
│   └── game.zip
└── cache/
    └── game_cache.zip

PSP (folder format):

/PSP/GAME/CPS2PSP/
├── roms/
│   └── game.zip
└── cache/
    └── game_cache/

PS2 (raw format — default):

mass:/CPS2PSP/
├── roms/
│   └── game.zip
└── cache/
    └── game.cache

Building from Source

Windows

mkdir build && cd build
cmake .. -DTARGET=CPS2
cmake --build .

Linux/macOS

mkdir build && cd build
cmake .. -DTARGET=CPS2
make

WebAssembly

mkdir build && cd build
emcmake cmake .. -DTARGET=CPS2
emmake make

Notes

Parent ROM sets must be in the same directory as the game ROM
The converter requires rominfo.cps2 file to be present in the same directory as the executable
Cache files are version-specific - regenerate if you update the emulator
Some games fully fit in memory and don’t require cache conversion

Cache Format Comparison

The emulator supports reading caches in raw file, zip, and folder formats. The table below compares them from a memory and performance perspective to help you choose the right format for your target platform.

Memory

Aspect	Raw File (default)	ZIP (`-zip`)	Folder (`-folder`)
Persistent open FD	1 file descriptor held open	Zip archive kept open (central directory in RAM)	None — open/read/close per block
ZIP central directory overhead	—	~32 bytes × num_entries	—
Block metadata	`block_offset[0x200]` = 2 KB	`block_empty[0x200]` = 512 B	`block_empty[0x200]` = 512 B
Sleep/resume cost	`close()`/`open()` 1 FD	`zip_close()`/`zip_open()` (re-parse central dir)	Nothing to do
Overall RAM overhead	Lowest	Medium	Lowest

Read Performance

Aspect	Raw File (default)	ZIP (`-zip`)	Folder (`-folder`)
Cache miss (block load)	`lseek()` + `read()` — 1 syscall pair, direct offset	`zopen()` → scan zip dir + `zread()` decompress 64 KB + `zclose()` — slowest	`open()` + `read()` + `close()` — 3 syscalls, no decompression
Cache hit	LRU pointer update only	LRU pointer update only	LRU pointer update only
I/O pattern	Random seek in single file ✅	Sequential scan of zip entries + inflate ❌	Path lookup + read small file 🔶
Decompression CPU	None	zlib `inflate()` per 64 KB block — significant on PSP/PS2	None
Startup (`fill_cache`)	Sequential `lseek`+`read` — fast	Open+decompress+close each block — slowest	Open+read+close each block — moderate

Disk / Storage

Aspect	Raw File (default)	ZIP (`-zip`)	Folder (`-folder`)
Disk size	Largest — offset table + uncompressed blocks, padded to 64 KB alignment	Smallest — deflate typically 30–70% compression	Same as raw — uncompressed blocks + metadata
File count	1 file	1 file	Many files (up to 512 blocks + `cache_info`)
Filesystem friendliness	✅ Best	✅ Good	⚠️ FAT16/FAT32 may struggle with 500+ entries (PSP Memory Stick)

Recommendation per Platform

Platform	Best format	Reason
PSP	Raw file (default)	Weakest CPU; `lseek`/`read` is the cheapest cache miss path. Single FD. FAT16 hates many files.
PS2	Raw file (default)	Same — limited CPU, limited I/O drivers.
Desktop	Any (zip for disk savings)	CPU is a non-issue; zip saves ~50% disk with negligible cost.
WASM / Web	ZIP	Single HTTP download; in-memory inflate is fast in browser.

Troubleshooting

“ROM not found” error: - Ensure the ROM filename matches entries in rominfo.cps2 - Check that parent ROMs are available for clone sets

Game runs without conversion: - Some smaller CPS2 games don’t require cache files - The emulator will load the ROM directly if it fits in memory