Sega Mega Drive to GameCube controller adapter

Also supports Xbox controllers (Xbox 360 / One / Series) and standard USB HID gamepads (with layout similar to PS4 DualShock 4) with USB Type-C OTG adapter.

USB gamepads support can be limited because of GameCube controller port does not provide sufficient +5V power (PS5 DualSense not working).

Bluetooth dongles are not supported unless they emulate standard USB HID device.

DualShock 3 / DualShock 4 / Xbox One / Series controllers are recommended.

Tested with USB controlers:

Model	State
Xbox 360 USB	Working
Xbox One Model 1537	Working
Xbox Series Model 1914	Working
PS3 DualShock 3 CECHZC2R	Working
PS4 DualShock 4 CUH-ZCT1E	Working
PS5 DualSense CFI-ZCT1W	Not working Unsufficient power

Schematics

Bill of Materials

• GameCube controller replacement cable
• WaveShare RP2040-Zero board
• DB9 Male connector
• 12 wires (approx. 60 mm each); 3 wires for USB pads only

Buttons mapping

A/B, X/Y buttons mapping for USB gamepads matches Xbox controllers layout (reverse SNES A/B, X/Y).

Sega Mega Drive 6-button pad

src/main.cpp:

gc.a = smd.a;
gc.b = smd.b;
gc.x = smd.x;
gc.y = smd.y;

gc.l = smd.z;
gc.r = smd.c;

gc.start = smd.start;

gc.dLeft = smd.left;
gc.dRight = smd.right
gc.dDown = smd.down
gc.dUp = smd.up
gc.z = smd.mode

Xbox controllers

src/main.c:

gc.a = (buttons & XINPUT_GAMEPAD_A);
gc.b = (buttons & XINPUT_GAMEPAD_B);
gc.x = (buttons & XINPUT_GAMEPAD_X);
gc.y = (buttons & XINPUT_GAMEPAD_Y);

gc.start = (buttons & (XINPUT_GAMEPAD_START | XINPUT_GAMEPAD_GUIDE));

gc.dLeft = (buttons & XINPUT_GAMEPAD_DPAD_LEFT);
gc.dRight = (buttons & XINPUT_GAMEPAD_DPAD_RIGHT);
gc.dDown = (buttons & XINPUT_GAMEPAD_DPAD_DOWN);
gc.dUp = (buttons & XINPUT_GAMEPAD_DPAD_UP);

const uint8_t TRIGGER_CLICK_TRESHOLD = 32;
gc.l = pad->bLeftTrigger > TRIGGER_CLICK_TRESHOLD
gc.r = pad->bRightTrigger > TRIGGER_CLICK_TRESHOLD;

gc.z = (buttons & XINPUT_GAMEPAD_RIGHT_SHOULDER);

gc.xStick = int16_to_u8_biased(pad->sThumbLX);
gc.yStick = int16_to_u8_biased(pad->sThumbLY);

gc.cxStick = int16_to_u8_biased(pad->sThumbRX);
gc.cyStick = int16_to_u8_biased(pad->sThumbRY);

gc.analogL = pad->bLeftTrigger;
gc.analogR = pad->bRightTrigger;

Standard USB HID controllers (DualShock 4)

src/hid_gamecube_mapping.cpp:

REPORT_USAGE_PAGE_BUTTON, 1, MAP_GAMECUBE_BUTTON_X // Square -> X
REPORT_USAGE_PAGE_BUTTON, 2, MAP_GAMECUBE_BUTTON_A // Cross -> A
REPORT_USAGE_PAGE_BUTTON, 3, MAP_GAMECUBE_BUTTON_B // Circle -> B
REPORT_USAGE_PAGE_BUTTON, 4, MAP_GAMECUBE_BUTTON_Y // Triangle -> Y

REPORT_USAGE_PAGE_BUTTON, 6, MAP_GAMECUBE_BUTTON_Z // R1

// Note: DualShock S4 generates press event starting from minimum force,
// GameCube controller generates L/R clicks after maximum force to analog L/R axes applied.
// Can be replaced with mapping analog Rx/Ry axis with MAP_TYPE_THRESHOLD_ABOVE 192 (75%) to GameCube L/R.
REPORT_USAGE_PAGE_BUTTON, 7, MAP_GAMECUBE_BUTTON_L // L2 Digital
REPORT_USAGE_PAGE_BUTTON, 8, MAP_GAMECUBE_BUTTON_R // R2 Digital

REPORT_USAGE_PAGE_BUTTON, 10, MAP_GAMECUBE_BUTTON_START // Options -> Start

// Left analog
REPORT_USAGE_X, MAP_GAMECUBE_AXIS_X // LX
REPORT_USAGE_Y, MAP_GAMECUBE_AXIS_Y // LY, inverted
// Right analog
REPORT_USAGE_Z, MAP_GAMECUBE_AXIS_CX // RX 
REPORT_USAGE_Rz, MAP_GAMECUBE_AXIS_CY // RY, inverted
// Analog left/right triggers
REPORT_USAGE_Rx, MAP_GAMECUBE_AXIS_L // LT / R2
REPORT_USAGE_Ry, MAP_GAMECUBE_AXIS_R // RT / R2

// POV/HAT switch (also D-PAD in most cases)
// 0 on hat switch, just press up
MAP_GAMECUBE_U, HID_GAMEPAD_HAT_UP
// 1 on hat switch, press up and right
HID_GAMEPAD_HAT_UP_RIGHT, MAP_GAMECUBE_U
HID_GAMEPAD_HAT_UP_RIGHT, MAP_GAMECUBE_R
// 2 on hat switch, press right
HID_GAMEPAD_HAT_RIGHT, MAP_GAMECUBE_R
// 3 on hat, press right and down
HID_GAMEPAD_HAT_DOWN_RIGHT, MAP_GAMECUBE_R
HID_GAMEPAD_HAT_DOWN_RIGHT, MAP_GAMECUBE_D
// 4 on hat, press down
HID_GAMEPAD_HAT_DOWN, MAP_GAMECUBE_D
// 5 on hat, press down and left
HID_GAMEPAD_HAT_DOWN_LEFT, MAP_GAMECUBE_D
HID_GAMEPAD_HAT_DOWN_LEFT, MAP_GAMECUBE_L
// 6 on hat, press left
HID_GAMEPAD_HAT_LEFT, MAP_GAMECUBE_L
// 7 on hat, press left and up
HID_GAMEPAD_HAT_UP_LEFT, MAP_GAMECUBE_L
HID_GAMEPAD_HAT_UP_LEFT, MAP_GAMECUBE_U

// Rarely used
REPORT_USAGE_DPAD_UP, MAP_GAMECUBE_U
REPORT_USAGE_DPAD_DOWN, MAP_GAMECUBE_D
REPORT_USAGE_DPAD_RIGHT, MAP_GAMECUBE_R
REPORT_USAGE_DPAD_LEFT, MAP_GAMECUBE_L

PS4 DualShock 4 / PS5 DualSense used as reference for buttons IDs:
Button 0x01 - Square button
Button 0x02 - Cross button
Button 0x03 - Circle button
Button 0x04 - Triangle button
Button 0x05 - L1 button
Button 0x06 - R1 button
Button 0x07 - L2 button
Button 0x08 - R2 button
Button 0x09 - Share button
Button 0x0A - Options button
Button 0x0B - L3 button
Button 0x0C - R3 button
Button 0x0D - PS button
Button 0x0E - Touchpad button

DualShock 3

gc.a = ps3->button_cross;
gc.b = ps3->button_circle;
gc.x = ps3->button_square;
gc.y = ps3->button_triangle;
gc.start = ps3->button_start;

gc.dLeft = ps3->dpad_left;
gc.dRight = ps3->dpad_right;
gc.dDown = ps3->dpad_down;
gc.dUp = ps3->dpad_up;

const uint8_t TRIGGER_CLICK_TRESHOLD = 32;
gc.l = ps3->trigger_l2_analog > TRIGGER_CLICK_TRESHOLD;
gc.r = ps3->trigger_r2_analog > TRIGGER_CLICK_TRESHOLD;

gc.z = ps3->trigger_r1;

gc.xStick = ps3->joy_left_x;
gc.yStick = UINT8_MAX - ps3->joy_left_y;
gc.cxStick = ps3->joy_right_x;
gc.cyStick = UINT8_MAX - ps3->joy_right_y;
gc.analogL = ps3->trigger_l2_analog;
gc.analogR = ps3->trigger_r2_analog;

Input lag / latency

For Sega Mega Drive 6 buttons pad delay mostly defined by GameCube controller JoyBus speed if queried once per frame:
3 bytes console request + 8 bytes response @250kbps: protocol delay ~0.35 ms.

USB pads are reports its state at fixed rate, mostly 125Hz (8 ms latency).
DualShock 4 has a default wired polling rate 250Hz (4ms latency)
Xbox Series Controller Model 1914: default USB poll rate 125Hz (8 ms latency)

How to flash firmware

• Connect RP2040-Zero to PC
• Press BOOT and then RESET, new drive will appear
• Drop SMD2GC.uf2 from Releases section to new drive

How to build firmware

Checkhout git repository.

git submodule update --init

Easy way:

• Install Visual Studio Code and official Raspberry Pi Pico Visual Studio Code extension
• On "Raspberry Pi Pico Project" left tab: "Import project"
• "Configure Cmake", use toolchain installed with Raspberry Pi Pico Visual Studio Code extension
• "Compile Project"
• "Run Project (USB)". Board should be in BOOT mode.

Hard way:

• Install Raspberry Pi Pico SDK, ARM-GCC toolchain, CMake.

Credits

• Julien Bernard - Joybus protocol (Gamecube controller) implementation for the Raspberry Pi Pico
• riguetti - unused code cleanup
• Andrew Tait - USB HID descriptors and reports parsing code
• Ryzee119 - Xbox/Xinpit controllers support module for TinyUSB library