//Leonardo & ProMicroの場合
#define SERIAL Serial1

//ProMiniの場合
//#define SERIAL Serial

#define RST 4 //リセット要求
#define RDY 5 //送信可能
#define RXD 1 //データ送信
#define RTY 6 //再送要求

//キーボード
#define DATA  8
#define CLOCK 2 //割り込みに使用

#define BUFFER_SIZE 32

static volatile uint8_t keyBuffer[BUFFER_SIZE];
static volatile uint8_t head, tail;

uint8_t ps2code;
bool keybreak;

void setup() {
  pinMode(RST, INPUT);
  pinMode(RDY, INPUT);
  //pinMode(RXD, OUTPUT);
  pinMode(RTY, INPUT);
  pinMode(CLOCK, INPUT_PULLUP);
  pinMode(DATA, INPUT_PULLUP);

  //ハードウェアシリアル初期化
  //19.2kbps 8ビット 奇数パリティ ストップビット1ビット
  SERIAL.begin(19200, SERIAL_8O1);
  SERIAL.write(0); //何故か必要
  
  head = 0;
  tail = 0;
  keybreak = false;

  attachInterrupt(digitalPinToInterrupt(CLOCK), keyCodeInt, FALLING);
}

void loop()
{
  //PC98の状態
  while(digitalRead(RDY) == HIGH) //送信不可
    delayMicroseconds(1);
  if(digitalRead(RTY) == LOW) //再送要求
    SERIAL.write(0); //ダミーデータ
  if(digitalRead(RST) == LOW) //リセット要求
    delayMicroseconds(30);
    
  ps2code = getKeyCode();
  switch(ps2code)
  {
    case 0xF0: //キーリリース
      keybreak = true;
      break;
    case 0x77: //Num Lock
      if(keybreak)
      {
        SERIAL.write(0x3F | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x3F); //HELP
      break;
    case 0x4A: //'/'(E0 4A)
      if(keybreak)
      {
        SERIAL.write(0x41 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x41);
      break;
    case 0x7C: //*
      if(keybreak)
      {
        SERIAL.write(0x45 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x45);
      break;
    case 0x7B: //-
      if(keybreak)
      {
        SERIAL.write(0x40 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x40);
      break;
    case 0x79: //+
      if(keybreak)
      {
        SERIAL.write(0x49 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x49);
      break;
    case 0x6C: //7
      if(keybreak)
      {
        SERIAL.write(0x42 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x42);
      break;
    case 0x75: //8
      if(keybreak)
      {
        SERIAL.write(0x43 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x43);
      break;
    case 0x7D: //9
      if(keybreak)
      {
        SERIAL.write(0x44 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x44);
      break;
    case 0x6B: //4
      if(keybreak)
      {
        SERIAL.write(0x46 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x46);
      break;
    case 0x73: //5
      if(keybreak)
      {
        SERIAL.write(0x47 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x47);
      break;
    case 0x74: //6
      if(keybreak)
      {
        SERIAL.write(0x48 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x48);
      break;
    case 0x69: //1
      if(keybreak)
      {
        SERIAL.write(0x4A | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x4A);
      break;
    case 0x72: //2
      if(keybreak)
      {
        SERIAL.write(0x4B | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x4B);
      break;
    case 0x7A: //3
      if(keybreak)
      {
        SERIAL.write(0x4C | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x4C);
      break;
    case 0x70: //0
      if(keybreak)
      {
        SERIAL.write(0x4E | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x4E);
      break;
    case 0x71: //.
      if(keybreak)
      {
        SERIAL.write(0x50 | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x50);
      break;
    case 0x5A: //Enter(E0 5A)
      if(keybreak)
      {
        SERIAL.write(0x1C | 0x80);
        keybreak = false;
      }
      else
        SERIAL.write(0x1C);
      break;
  }
}

//キーコードのバッファからコードを取り出す
static inline uint8_t getKeyCode(void)
{
  uint8_t ret;

  if (head == tail)
    return 0;

  ret = keyBuffer[head++];
  if (head == BUFFER_SIZE)
  {
    head = 0;
  }

  return ret;
}

//キーボードからキーコードを受け取る(割り込みエントリ)
void keyCodeInt(void)
{
  static uint8_t past = 0;
  static uint8_t counter = 0;
  static uint8_t code;
  static uint8_t parity;
  uint8_t now, onebit, p;

  onebit = digitalRead(DATA);

  now = millis();
  if (now - past > 250)
    counter = 0;
  past = now;

  switch (counter++)
  {
    case 0: //スタートビット
      code = 0;
      parity = 0;
      break;
    case 1:
    case 2:
    case 3:
    case 4:
    case 5:
    case 6:
    case 7:
    case 8:
      code |= onebit << counter - 2;
      parity += onebit;
      break;
    case 9:
      if (onebit == (~parity & 1))
      {
        //キーバッファにコードを入れる
        p = tail;
        keyBuffer[p++] = code;
        if (p == BUFFER_SIZE)
          p = 0;
        if (p == head)
          p = tail;
        else
          tail = p;
      }
      break;
    case 10: //ストップビット
      counter = 0;
      break;
  }
}