SMD2Wii

SMD2Wii - adapter for Sega Mega Drive controller to Wii remote.

Adapter emulates Wii Classic Controller with Sega Mega Drive / Genesis 3/6-button controller and can be used with homebrew emulators like Genesis Plus GX and selected Wii Virtual Console Games.
Work not confirmed for NES Classic Mini / SNES Classic Mini.

The goal is to connect SMD 6-button controller to Wii as cheap and simple as possible.
For NES / SNES emulators excellent Nintendo Classic Mini Controller / Nintendo SNES Classic Mini Controller suggested.

Project based on Cluster's nes2wii project with following changes:

Controller replaced with simpler / cheaper ATmega8A
Deleted all other platforms and second SMD pad support from source code and schematics
New smaller PCB
Fixed SMD 6-button pad state query errors
KiCad 7.0 schematic and PCB sources added

Schematics

Board:

Assembled board preview without Wiimote connector:

Fuses

Low fuse: 0xC4
High fuse: 0xD9

Compiling from source

Windows:
Install WinAVR-20100110-install.exe
make all

CH341A programmer and NeoProgrammer V2.2 software can be used for firmware .hex flashing.

Tested with

ATmega8A-U, 8MHz
Third party 6-buttons Sega Mega Drive controller with Mode button ("Retro Genesis 16 Bit ACSg11")
Software: Genesis Plus GX, FCE Ultra GX, WiiMednafen, RetroArch

Modes

There are three modes for controller d-pad:

Mode #1 - d-pad works as left analog stick and d-pad on classic controller at the same time
Mode #2 - d-pad works as left analog stick only
Mode #3 - d-pad works as d-pad only

Mode 1 selected by default.

You can hold Start+B+C for a few seconds to change mode. Red led will blink 1/2/3 times indicating new mode.

Bill of materials

ATMEGA8A-U TQFP32
DB9 PCB Connector Angle (DSUB-9 Male Horizontal P2.77x2.84mm Edge Pin Offset 7.70mm Mounting Holes Offset 9.12mm)
Wii controller 6 Pin 90 degree male connector
SMD 1206 Resistor 2.2k(222) x3
SMD 1206 Capacitor 0.1(104) uF x1
(only for programming) Connector PinHeader 2.54mm 1x06 Vertical
(optional) Electrolytic Capacitor Radial D5.0mm P2.50mm 4.7 uF
(optional) SMD 1206 Resistor 400 Ohm x2
(optional) SMD 1206 LED Red x1
(optional) SMD 1206 LED Green x1

Notes

About delays and interrupts

SMD controller polled every 5 ms. Wiimote classic controller query interrupt disabled during the poll (not sure if interrupt is delayed or cancelled).
Worst case scenario additional input delay is about 5-6 ms (or one frame).
Current code:

void gamepads_query()
{
	_delay_ms(5); // Must be >= 3 to give 6-button controller time to reset

	cli(); // Disable wiimote poll interrupt

	// 8 iterations for read controller state.
	for (b = 0; b < 8; b++)
	{
		// Were can be enough CPU ticks in loop cycle without additional delay
		// for short delay to stabilize outputs in controller (needs to be tested with different controllers)
		...read pad pins
		...invert SELECT pin
	}

	sei(); // Enable interrupt

See gamepads.c code comments for more details.

Buttons mapping

Classic controller to SMD buttons mapping:

a = smd.c;
b = smd.b;
x = smd.y;
y = smd.a;
l = smd.x;
r = smd.z;
select = smd.mode;
start = smd.start;

Author(s)

Original firmware and schematics for ATMEGA16A:
Alexey 'Cluster' Avdyukhin https://github.com/ClusterM
https://github.com/ClusterM/nes2wii

Sega MD 6-buttons query code and documentation:
https://github.com/MickGyver/DaemonBite-Retro-Controllers-USB
https://github.com/jonthysell/SegaController

SMD2Wii modifications:
probotector

proboterror/smd2wii