Reverse Engineered Bubble Bobble for Commodore 64

A complete reverse-engineering of Bubble Bobble on the Commodore 64, producing fully documented, reassembleable source code.

All executable code has been reverse engineered and converted to documented 6502 assembly. The source assembles to a binary 100% identical to the original game.

Remaining work: Convert hardcoded addresses to labels so the assembler can recalculate addresses when code is added or removed.

• cc65 - 6502 cross-compiler suite
  • Fedora/RHEL: sudo dnf install cc65
  • Debian/Ubuntu: sudo apt install cc65
  • macOS: brew install cc65

cd build
make              # Build the game
make verify       # Build and verify against original
make clean        # Clean build artifacts

The default build produces a raw memory image (rebb64-raw.prg) that loads at $0400. This is the decompressed game data without a startup stub, so it won't auto-run directly. The entry point is at $4830.

To create a runnable PRG, use TSCrunch (prebuilt binaries available):

make release    # requires tscrunch in PATH, outputs rebb64.prg

Or manually:

tscrunch -p -x '$4830' rebb64-raw.prg rebb64.prg

Edit src/master.s and change values:

; Change starting lives from 4 to 9:
starting_lives:
        lda     #$09                ; was #$04

Replace instructions with same byte count:

; Infinite lives - replace 3-byte DEC with 3 NOPs:
lives_decrement:
        nop                         ; ea (was: dec D_045A,x)
        nop                         ; ea
        nop                         ; ea

Note: There is currently no free space in the game binary. The memory region $8B00-$8EFF (previously documented as free) is actively used as a screen buffer and is overwritten every time a level starts.

For larger modifications, you have two options:

1. Replace existing code with your custom routine (maintaining exact byte count)
2. Use the cassette buffer at $033C-$03FB (192 bytes) which is unused during gameplay:

; Replace original instruction with JSR to your code:
lives_decrement:
        jsr     custom_lives_handler

; Add your code in cassette buffer (unused during gameplay):
.org $033C
custom_lives_handler:
        lda     cheat_flag
        bne     @skip
        dec     D_045A,x
@skip:  rts

Warning: The cassette buffer ($033C) may be used during disk/tape operations. Test thoroughly.

Graphics and audio are in separate binary files for easy editing:

Edit with: SpritePad, CharPad, or hex editor. Rebuild to see changes.

Modified code must produce exactly the same byte count until full label conversion is complete. Adding/removing bytes will break absolute addresses. Graphics files can be freely modified (fixed-size).

These locations are labeled for easy modification:

rebb64/
├── README.md
├── docs/
│   └── TECHNICAL.md         # Detailed technical documentation
├── src/
│   ├── master.s             # Main source file
│   ├── loadaddr.s           # PRG load address header
│   └── *.s                  # Game modules (25 files)
├── data/
│   └── *.bin                # Graphics, music, level data
└── build/
    ├── Makefile
    └── c64-prg.cfg

Build is verified against SHA256 of the original decompressed PRG:

fdba2390782653ba2533b2d87c44c8f0480ab18968a2c0ccc0cef8300fcee7b6

See docs/TECHNICAL.md for:

• Complete memory map
• Key game routines reference
• Detailed module documentation
• Algorithm explanations

This is a reverse-engineering project for educational purposes. Bubble Bobble is Copyright (c) 1986 Taito Corporation. C64 version by Firebird Software.

• Original game: Taito Corporation
• C64 conversion: Software Creations (Stephen Ruddy), published by Firebird Software
• Reverse engineering: This project