// DMX reciever for atmega328p
// it consumes the USART, so serial transfers cant be used

#define SIZE 512 // max frame size, if you want to do it this way
volatile byte dmx_buffer[SIZE]; // allocate buffer space
unsigned int dmx_ptr = 0;
byte dmx_state = 0; // state tracker

void setup() {
  // initialize uart for data transfer
  UBRR0H = ((F_CPU/250000/16) - 1) >> 8;
  UBRR0L = ((F_CPU/250000/16) - 1);
  UCSR0A = 1<<UDRE0;
  UCSR0C = 1<<USBS0 | 1<<UCSZ01 | 1<<UCSZ00; // 2 stop bits,8 data bitss
  UCSR0B = 1<<RXCIE0 | 1<<RXEN0; // turn it on, set RX complete intrrupt on
}

void loop() {
  while(1);
}

ISR(USART_RX_vect) {
  // check if BREAK byte
  if (UCSR0A & (1<<FE0)) {
    byte temp = UDR0; // get data to clear buffer
    dmx_state = 1; // set to slot0 byte waiting
  }
  // check for state 2 first as its most probable
  else if (dmx_state == 2) {
    dmx_buffer[dmx_ptr] = UDR0; // store data
    dmx_ptr++;
    if (dmx_ptr >= SIZE) {
      dmx_state = 0; // last byte recieved or error
    }
  }
  else if (dmx_state == 1) {
    // check if slot0 = 0
    if (UDR0) {
      dmx_state = 0; // error - reset reciever
    }
    else {
      dmx_ptr = 0; // reset buffer pointer to beginning
      dmx_state = 2; // set to data waiting
    }
  }
  else {
    byte temp = UDR0; // get data to flush buffer
    dmx_state = 0; // reset - bad condition or done
  }
}