Super Mario Kart — Static Recompilation

Static recompilation of Super Mario Kart (SNES, 1992) from WDC 65C816 assembly to native C code, playable on modern hardware via SDL2.

Part of the sp00nznet recompilation portfolio. This is the first SNES (65816 CPU) target in the series.

Status

48 recompiled functions — game boots through the title screen with full rendering, accepts joypad input, and transitions through the mode select and character select screens. DSP-1 coprocessor fully emulated via LakeSnes HLE backend.

What works

• Full boot chain: reset vector → hardware init → WRAM clear → PPU/APU/DSP-1 setup → Mode 7 angle table
• NMI handler with state dispatch, brightness fading, OAM DMA
• Main loop with state machine (idle → init → title → mode select → character select)
• Custom tile/tilemap decompressor ($84:E09E) — all 7 compression modes + E0+ extended counts
• Title screen transition: PPU register setup, VRAM tile/tilemap loading, palette decompression
• Real palette data loaded from ROM → CGRAM (256 colors)
• All 3 BG layers rendering correctly (Mode 1: title banner, hills, text)
• Sprite tile DMA pipeline: per-frame staging buffer → NMI DMA consumer → VRAM
• 8-slot sprite animation state machine with Y interpolation and phase milestones
• OAM builder: sprite slots → screen coords → OAM entries with proper tile/attr/priority
• Joypad input: SDL keyboard → SNES auto-joypad → WRAM with edge detection
• HDMA channel 1: indirect mode window masking ($2126/$2127)
• Mode select screen (state $14): graphics decompression, PPU init, simple menu input
• Character select screen (state $06): PPU Mode 0, tile DMA, palette loading, 8-character grid navigation with D-pad, confirm/cancel, transition trigger
• SRAM checksum validation and save data erase menu (button-gated, matching original logic)
• LakeSnes PPU renders all 224 scanlines per frame
• SDL2 window at 768×672 (3× scale), 60fps vsync, keyboard input

What's next

• Mode select screen graphics (text overlays for GP/Match Race/Battle Mode)
• Character portraits on the character select grid
• Race screen (Mode 7 rendering, DSP-1 projection math, full gameplay — DSP-1 HLE backend now active)

Architecture

┌─────────────────────────────────────────────────┐
│                 smk_launcher                      │
│  ┌──────────────────────────────────────────┐    │
│  │  src/recomp/ — 48 Recompiled functions   │    │
│  │  smk_boot.c  — NMI, state machine, input │    │
│  │  smk_init.c  — Init, transition dispatch │    │
│  │  smk_title.c — Decompressor, PPU, menus  │    │
│  └──────────────────────────────────────────┘    │
│                       │                           │
│              bus_read8 / bus_write8               │
│                       │                           │
│  ┌──────────────────────────────────────────┐    │
│  │  snesrecomp (ext/snesrecomp/)            │    │
│  │  ┌────────────────────────────────────┐  │    │
│  │  │  LakeSnes — Cycle-accurate SNES HW │  │    │
│  │  │  Real PPU (Mode 0-7, sprites, etc) │  │    │
│  │  │  Real SPC700 + DSP audio           │  │    │
│  │  │  Real DMA (GPDMA + HDMA)           │  │    │
│  │  │  Full memory bus routing            │  │    │
│  │  └────────────────────────────────────┘  │    │
│  │  SDL2 platform (window, audio, input)    │    │
│  └──────────────────────────────────────────┘    │
└─────────────────────────────────────────────────┘

Recompiled game code acts as the CPU — it calls bus_read8(bank, addr) / bus_write8(bank, addr, val) which route through LakeSnes's real memory bus to the actual PPU, APU, DMA, and cartridge hardware. The PPU renders scanlines, the APU processes audio, and DMA transfers happen exactly as on real hardware.

Controls

Key	SNES Button
Arrow keys	D-pad
Z	B
X	Y
A	A
S	X
Q	L
W	R
Enter	Start
Right Shift	Select
Escape	Quit

Building

Prerequisites

• CMake 3.16+
• Visual Studio 2022 (MSVC)
• SDL2 via vcpkg: vcpkg install sdl2:x64-windows
• Python 3.10+ (for disassembler and analysis tools)

Build

cmake -B build -G "Visual Studio 17 2022" -A x64 \
  -DCMAKE_TOOLCHAIN_FILE=C:/vcpkg/scripts/buildsystems/vcpkg.cmake

cmake --build build --config Debug

Run

build/Debug/smk_launcher.exe

The ROM file is not included — supply your own US v1.0 copy (MD5: 7f25ce5a283d902694c52fb1152fa61a).

Decompressor

The custom decompressor at $84:E09E handles SMK's tile/tilemap compression format:

Mode	Encoding	Description
$00	Raw	Copy N bytes from stream
$20	RLE	Repeat 1 byte N times
$40	Word fill	Alternate 2 bytes for N entries
$60	Inc fill	Store incrementing byte N times
$80	Backref	Copy from earlier in buffer (abs offset + base)
$A0	Inv backref	Copy with XOR $FF (inverted)
$C0	Byte backref	Copy from buf_pos - offset (1-byte offset)

Commands $E0–$FE use extended 10-bit counts: 1 data byte + cmd bits 0-1 as high bits.

Project Structure

├── include/smk/       cpu_ops.h (65816 instruction helpers), functions.h
├── src/
│   ├── recomp/        Recompiled game functions (smk_boot.c, smk_init.c, smk_title.c)
│   └── main/          main.c — entry point, frame loop
├── ext/snesrecomp/    snesrecomp library (LakeSnes backend + SDL2 platform)
└── tools/
    ├── disasm/        65816 disassembler (M/X flag tracking, all addressing modes)
    └── mesen/         Mesen2 trace scripts + parsers

ROM Details

Field	Value
Title	SUPER MARIO KART
System	Super Nintendo (SNES)
CPU	WDC 65C816 @ 3.58 MHz
Coprocessor	DSP-1 (math) + SPC700 (audio)
Mapping	HiROM FastROM
Size	512 KB (8 × 64 KB banks, C0–C7)
SRAM	2 KB
Region	USA
CRC32	CD80DB86

Key References

• Yoshifanatic1/Super-Mario-Kart-Disassembly — Full 65816 + SPC700 disassembly (Asar)
• jvipond/super_mario_kart_disassembly — Trace-based disassembly with Python tooling
• jvipond/super_mario_kart_recompilation — Prior LLVM-based recomp attempt
• MrL314/smk-spc700-disassembly — SPC700 audio driver disassembly
• LakeSnes — Cycle-accurate SNES emulator in C (hardware backend)

License

This project contains no Nintendo copyrighted material. The ROM file is not included and must be legally obtained by the user.