#define PIN_DIR 2
#define PIN_STEP 3
#define PIN_ENABLE 4
#define PIN_ENDSTOP 5

char rcv;
char cmd;
char s_enable = true;
char s_endstop = false;

void setup() {
   pinMode(PIN_ENABLE, OUTPUT);
   digitalWrite(PIN_ENABLE, LOW);
   pinMode(PIN_DIR, OUTPUT);
   pinMode(PIN_STEP, OUTPUT);
   delay(500);
   Serial.begin(250000);
   // initial flush
   while (Serial.available()) {
      Serial.read();
   }
}

void loop() {
  char cmd;
  char snd;
  if (Serial.available()) {
    rcv = Serial.read();
    cmd = rcv & 0b11;
    if (cmd != 0b00) {
      if (cmd == 0b11) {
        s_enable = !s_enable;
        digitalWrite(PIN_ENABLE, s_enable ? LOW : HIGH);
      } else {
        digitalWrite(PIN_DIR, cmd & 0b01 ? LOW : HIGH);
        digitalWrite(PIN_STEP, HIGH);
        delayMicroseconds(50);
        digitalWrite(PIN_STEP, LOW);
      }
    }
    snd = ((rcv >> 2) & 0b00111111) | (s_endstop << 6) | (s_enable << 7);
    Serial.write(snd);
  }
  int val = analogRead(PIN_ENDSTOP);
  s_endstop = val < 850;
}