Yet another library to read Sega Mega Drive (aka Sega Genesis) gamepad.
Supports both three and six buttons controllers.

• Download this repo as .zip file: https://github.com/IvoryRubble/ArduinoSegaGamepadLibrary/archive/master.zip
• In the Arduino IDE select Sketch > Include Library > Add .ZIP Library.... Browse to where the downloaded ZIP file is located and click Open. The SegaGamepad library's examples will now appear under File > Examples > SegaGamepad.

Or simply open library manager in Arduino IDE (Tools > Manage Libraries) and search for SegaGamepad.

Library is also available in PlatformIO registry:
https://registry.platformio.org/libraries/ivoryrubble/SegaGamepad

Gamepad protocol description:
http://web.archive.org/web/20171229105419/http://www.cs.cmu.edu/~chuck/infopg/segasix.txt
https://github.com/jonthysell/SegaController/wiki/How-To-Read-Sega-Controllers

Gamepad protocol reverse engineering:
https://www.raspberryfield.life/2019/03/25/sega-mega-drive-genesis-6-button-xyz-controller/#SMD6-protocol-overview

Another good library:
https://github.com/jonthysell/SegaController

Sega Mega Drive gamepad connector pinout, female DB9 plug:

   +----------- pin5, +5V
   | +--------- pin4, set by gamepad            
   | | +------- pin3, set by gamepad  
   | | | +----- pin2, set by gamepad   
   | | | | +--- pin1, set by gamepad
   | | | | |            
+-------------+             
 \ O O O O O /                
  \ O O O O /                  
   +-------+                 
    | | | |
    | | | +---- pin6, set by gamepad
    | | +------ pin7, Select pin, set to 0 or 1 by microcontroller        
    | +-------- pin8, GND
    +---------- pin9, set by gamepad         

Connect pin8 and pin5 to GND and +5V.
Connect pin1, pin2, pin3, pin4, pin6, pin7, pin9 to microcontroller I/O pins.

Set correcponding pin1, pin2, pin3, pin4, pin6, pin7, pin9 numbers in SegaGamepad::SegaGamepad() constructor.
Optionally set custom delayBeforeReadMicros and delayBeforeNextUpdateMicros delays.
Example:

SegaGamepad segaGamepad(1, 2, 3, 4, 5, 6, 7);

Call SegaGamepad::init() method in setup() procedure to initialize microcontroller ports for gamepad.
Example:

segaGamepad.init(); 

Call SegaGamepad::update() method to read new values from controller.
Then you can keys get values from segaGamepad object fields. True value means corresponding key is pressed.
You also can check if controller is connected by reading isConnected flag.
And you can check type of controller (three or six buttons) by reading isSixBtns flag.
When controller is not connected then isConnected flag is set to False, all buttons values are set to False, is isSixBtns flag is set to False.
Example:

segaGamepad.update();
Serial.println(segaGamepad.isConnected);
Serial.println(segaGamepad.btnUp);
Serial.println(segaGamepad.btnA);
Serial.println(segaGamepad.btnStart);