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ROMCNV - Neo-Geo MVS ROM Converter

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

Why Convert ROMs?

Neo-Geo MVS ROMs often contain graphics data larger than 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, enabling playback of games that would otherwise not fit in memory.

Supported Platforms

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

Usage

Basic Usage

Convert a single ROM:

romcnv_mvs /path/to/game.zip

Command Line Options

Option	Description
`-all`	Convert all ROMs in the specified directory
`-zip`	Create a ZIP compressed cache file instead of a folder
`-batch`	Batch mode - don’t pause between conversions
`-slim`	PSP Slim mode - skip PCM cache for unencrypted games (reduces cache size)

Examples

Convert a single game:

romcnv_mvs "D:\roms\kof99.zip"

Convert multiple games in batch mode:

romcnv_mvs "D:\roms\garou.zip" -batch
romcnv_mvs "D:\roms\kof2002.zip" -batch
romcnv_mvs "D:\roms\kof2003.zip"

Convert all ROMs in a directory:

romcnv_mvs "D:\roms" -all

Convert with ZIP compression:

romcnv_mvs "D:\roms\kof99.zip" -zip

Convert for PSP Slim (reduced cache size):

romcnv_mvs "D:\roms\kof99.zip" -slim

Linux/macOS Examples

# Convert a single ROM
./romcnv_mvs /home/user/roms/kof99.zip

# Convert with ZIP compression
./romcnv_mvs /home/user/roms/kof99.zip -zip

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

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

# Convert with slim mode
./romcnv_mvs /home/user/roms/garou.zip -slim

Output

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

Both formats are supported by the emulator on all platforms.

File Structure for Emulators

PSP (folder format):

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

PSP (zip format):

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

PS2 (folder format):

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

PS2 (zip format):

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

Cache Format Comparison

The emulator supports reading caches in folder and zip 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	Folder (default)	ZIP (`-zip`)
Persistent open FD	1 (`crom` file kept open)	Zip archive kept open (central directory in RAM)
ZIP central directory overhead	—	~32 bytes × num_entries
Sleep/resume cost	`close()`/`open()` 1 FD	`zip_close()`/`zip_open()` (re-parse central dir)
Overall RAM overhead	Lowest	Medium

Read Performance

Aspect	Folder (default)	ZIP (`-zip`)
Cache miss (block load)	`lseek()` + `read()` — 1 syscall pair, direct offset	`zopen()` → scan zip dir + `zread()` decompress 64 KB + `zclose()` — slowest
Cache hit	LRU pointer update only	LRU pointer update only
I/O pattern	Random seek in single `crom` file ✅	Sequential scan of zip entries + inflate ❌
Decompression CPU	None	zlib `inflate()` per 64 KB block — significant on PSP/PS2
Startup (`fill_cache`)	Sequential `lseek`+`read` — fast	Open+decompress+close each block — slowest

Disk / Storage

Aspect	Folder (default)	ZIP (`-zip`)
Disk size	Larger — uncompressed blocks	Smallest — deflate typically 30–70% compression
File count	Multiple files (`cache_info`, `crom`, `srom`, `vrom`)	1 file
Filesystem friendliness	✅ Few large files	✅ Single file

Recommendation per Platform

Platform	Best format	Reason
PSP	Folder (default)	Weakest CPU; `lseek`/`read` on `crom` is the cheapest cache miss path. No decompression overhead.
PS2	Folder (default)	Same — limited CPU, limited I/O drivers.
Desktop	Either (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.

Building from Source

Windows

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

Linux/macOS

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

WebAssembly

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

Notes

Parent ROM sets must be in the same directory as the game ROM
The converter requires rominfo.mvs file to be present in the same directory as the executable
Cache files are version-specific - regenerate if you update the emulator

Troubleshooting

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

Large cache sizes: - Use -slim option for PSP Slim/PS Vita - Some games (especially later titles) require more cache space