teensy-gamepad.c

#include <stdint.h>

// GPIO pins used for connected gamepad
#define CLOCK 21
#define LATCH 20
#define DATA  19

#define DEVICE_TYPE_NES  0
#define DEVICE_TYPE_SNES 1

enum {
  NES_BUTTON_A,
  NES_BUTTON_B,
  NES_BUTTON_SELECT,
  NES_BUTTON_START,
  NES_DPAD_UP,
  NES_DPAD_DOWN,
  NES_DPAD_LEFT,
  NES_DPAD_RIGHT
} NES_BUTTON_MAP;

enum {
  SNES_BUTTON_B,
  SNES_BUTTON_Y,
  SNES_BUTTON_SELECT,
  SNES_BUTTON_START,
  SNES_DPAD_UP,
  SNES_DPAD_DOWN,
  SNES_DPAD_LEFT,
  SNES_DPAD_RIGHT,
  SNES_BUTTON_A,
  SNES_BUTTON_X,
  SNES_BUTTON_L,
  SNES_BUTTON_R,
} SNES_BUTTON_MAP;

uint8_t BUTTON_STATE[16];
uint8_t DEVICE_TYPE = 0;

// Delay for approx 100ns. Assumes 16Mhz AtMega CPU
void delay100ns()
{
  __asm__ __volatile__ ("nop\n\t");
  __asm__ __volatile__ ("nop\n\t");
}

void ReadInput(uint8_t *data, int num)
{
  int i;
  
  // Init
  digitalWrite(CLOCK, HIGH);
  
  // Take sample
  digitalWrite(LATCH, HIGH);
  delay100ns();
  digitalWrite(LATCH, LOW);
  
  // Read output
  for (i = 0; i < num; i++) {
    delay100ns();
    digitalWrite(CLOCK, LOW);
    
    // 1 = Off, 0 = On... Bit must be inverted
    data[i] = (~digitalRead(DATA)) & 0x1;
    
    delay100ns();
    digitalWrite(CLOCK, HIGH);
  }
}

int GetHatState()
{
  
  /*
  
          0
          UP
      315    45
 270 LT        RT 90
      225    135
          DN
          180
  
  */
  
  uint8_t x, y;
  const static int16_t dpad_lookup[4][4] = {
    { -1, 270,  90, -1},
    {  0, 315,  45, -1},
    {180, 225, 135, -1},
    { -1,  -1,  -1, -1}
  };
  
  y = BUTTON_STATE[NES_DPAD_UP] | (BUTTON_STATE[NES_DPAD_DOWN] << 1);
  x = BUTTON_STATE[NES_DPAD_LEFT] | (BUTTON_STATE[NES_DPAD_RIGHT] << 1);
  
  return dpad_lookup[y][x];
}

void ProcessInputNES()
{
  int hat0;
  
  ReadInput((uint8_t *)&BUTTON_STATE, 8);
  hat0 = GetHatState();
  
  Joystick.button(1, BUTTON_STATE[NES_BUTTON_A]);
  Joystick.button(2, BUTTON_STATE[NES_BUTTON_B]);
  Joystick.button(3, BUTTON_STATE[NES_BUTTON_SELECT]);
  Joystick.button(4, BUTTON_STATE[NES_BUTTON_START]);
  
  Joystick.hat(hat0);
}

void ProcessInputSNES()
{
  int hat0;
  
  ReadInput((uint8_t *)&BUTTON_STATE, 8);
  hat0 = GetHatState();
  
  Joystick.button(1, BUTTON_STATE[SNES_BUTTON_A]);
  Joystick.button(2, BUTTON_STATE[SNES_BUTTON_B]);
  Joystick.button(3, BUTTON_STATE[SNES_BUTTON_X]);
  Joystick.button(4, BUTTON_STATE[SNES_BUTTON_Y]);
  Joystick.button(5, BUTTON_STATE[SNES_BUTTON_L]);
  Joystick.button(6, BUTTON_STATE[SNES_BUTTON_R]);
  Joystick.button(7, BUTTON_STATE[SNES_BUTTON_SELECT]);
  Joystick.button(8, BUTTON_STATE[SNES_BUTTON_START]);
  
  Joystick.hat(hat0);
}

void setup() {
  pinMode(CLOCK, OUTPUT);
  pinMode(LATCH, OUTPUT);
  pinMode(DATA, INPUT);
}

void loop() {
  if (DEVICE_TYPE == DEVICE_TYPE_NES) {
    ProcessInputNES();
  } else {
    ProcessInputSNES();
  }
  
  delayMicroseconds(1);
}