Classification: Source Code / Assembly Asset Target Architecture: Motorola 68000 (Motorola 68000) Associated Project: Sonic the Hedgehog 2 (Sega Mega Drive) Probable Origin: Sega Technical Institute (STI) / Simon Wai Prototype
sonic2-w.68k is an executable binary file for the Sharp X68000 home computer. It contains an early, unfinished prototype of Sonic the Hedgehog 2 — not the Sega Genesis/Mega Drive version, but a completely separate port developed in 1992.
The filename follows X68000 conventions:
dd if=sonic2-w.68k of=sonic2_fixed.bin bs=512 seek=1 conv=notrunc
If you open sonic2-w.68k in a text editor (like Notepad++ or VS Code), you aren't met with graphics or sound. You are met with pure logic. Here is a stylized example of what a snippet looks like:
; ---------------------------------------------------------------------------
; Subroutine to update Sonic's speed based on player input
; ---------------------------------------------------------------------------
Sonic_Control:
move.w ($FFFFF604).w,d0 ; Read controller input
bclr #0,d0 ; Check up direction
beq.s .not_up
subq.w #1,$10(a0) ; Decrease Y velocity (jump/rise)
.not_up:
jsr (SpeedToPos).l ; Convert speed to position
rts
This is not C++. It is not Python. This is assembly language: the lowest human-readable form of code before raw binary. Inside sonic2-w.68k, you will find:
To the outside world, sonic2-w.68k looks like a cryptic artifact—a jumble of labels, hex addresses, and macros. But to thousands of developers, artists, and historians, it represents the ultimate act of digital archaeology. It is the Rosetta Stone that unlocked one of the most beloved platformers ever made. sonic2-w.68k
Whether you want to restore a lost level, fix a 30-year-old bug, or simply learn how the blue blur defied gravity, sonic2-w.68k is your starting line. It stands as a testament to what passionate fans can achieve when they refuse to let a piece of software become a closed, unreadable monolith.
So fire up your assembler. Open the file. And remember: every time Sonic double-jumps in a ROM hack, somewhere, a line of move.w inside sonic2-w.68k is smiling.
Further reading: Sonic Retro Wiki – "Disassemblies" | GitHub – sonic2-68k-disasm | YouTube – "Building Sonic 2 from Source" by drx
sonic2-w.68k is a central assembly source file used in the "Westside" or "GitHub" disassembly of Sonic the Hedgehog 2
for the Sega Genesis/Mega Drive. It contains the primary 68000 (68k) assembly code that defines how the game operates, from player physics to level logic. Technical Overview File Purpose
: It serves as the "master" assembly file that links together various sub-modules (like sprite data, sound drivers, and level layouts) during the build process. Architecture : Written for the Motorola 68000 CPU, the primary processor of the Sega Genesis. Disassembly Origin The filename follows X68000 conventions:
: This specific naming convention is often associated with the Sonic Retro
community's efforts to reverse-engineer the game into a human-readable and re-buildable format. Key Components Within the Code The file typically manages or includes pointers to: Engine Core
: The main game loop that handles vertical blanking (V-blank) and task scheduling. Collision & Physics
: Subroutines for Sonic and Tails' movement, including the famous "Sonic physics" (slopes, loops, and rolling). Object Management
: The system for spawning and tracking enemies (Badniks), rings, and monitors. Zone Logic : Pointers to the data for iconic levels like Chemical Plant Zone and the famously cut Hidden Palace Zone Use in Modding Developers use this file as a base for ROM Hacking . By modifying sonic2-w.68k , a programmer can: Change Character Abilities : Add the "Insta-Shield" or "Drop Dash" to Sonic. Fix Original Bugs
: Correct "spike bugs" or camera issues present in the 1992 release. Create New Bosses : Rewrite the logic for encounters like the Death Egg Robot dd if=sonic2-w
this specific file into a playable ROM, or are you looking for a specific subroutine within the code? Hidden Palace Zone (Sonic the Hedgehog 2)
The file serves three primary purposes in 2024 and beyond:
No article on sonic2-w.68k would be complete without addressing the elephant in the room: copyright. Sega technically owns the rights to the Sonic 2 source code. However, because sonic2-w.68k was created through clean-room reverse engineering (or, in some cases, direct disassembly of a commercial ROM), it exists in a legal limbo.
Sega has historically turned a blind eye to the disassembly for two reasons:
That said, distributing pre-compiled ROMs based on sonic2-w.68k is illegal. The file itself—a text document of assembly instructions—is generally considered protected free speech under transformative use, though this has never been tested in court.