Patching

Tools for applying and creating ROM patches.

ROM Patcher

Applies IPS, BPS, or xDelta patches to ROM files.

IPS Patches

  • Applies standard IPS format patches (International Patching System).
  • Supports RLE-encoded records for efficient patch data.
  • Handles optional truncation records that resize the output file.
  • The EOF marker is validated before patching.

BPS Patches

  • Applies BPS format patches (Beat Patching System).
  • Full CRC32 validation of source ROM, target ROM, and patch data.
  • Supports SourceRead, TargetRead, SourceCopy, and TargetCopy actions.
  • If the source ROM CRC32 does not match the patch header, an error is raised indicating the wrong source file.

xDelta Patches

  • Applies xDelta/VCDIFF format patches (RFC 3284).
  • Supports all standard VCDIFF instruction types: ADD, RUN, and COPY.
  • Full address cache implementation (NEAR and SAME caches) for efficient COPY address decoding.
  • Adler-32 checksum verification of target windows (xdelta3 extension).
  • Supports multi-window patches and VCD_SOURCE/VCD_TARGET window modes.

Usage

  1. Select the source ROM (the unmodified file).
  2. Select the patch file (.ips, .bps, .xdelta, or .vcdiff).
  3. Choose an output path or let the tool generate one automatically.
  4. Click Apply Patch.

IPS Patch Creator

Creates IPS patches by comparing an original ROM with a modified version.

How It Works

  1. Select the original ROM and the modified ROM.
  2. The tool analyzes both files and shows:
    • File sizes of each ROM
    • Number of differing bytes
    • Whether the difference fits the IPS format (max 16 MB)
  3. Click Create Patch to generate the .ips file.

Details

  • Uses RLE compression for sequences of repeated byte values, producing smaller patches.
  • Maximum supported file size is 16 MB (IPS format limitation).
  • If the modified ROM is shorter than the original, a truncation record is included so the patched output is the correct size.