#include <avr/io.h>
  #include <util/delay.h>
  
  #define SERIAL_BAUDE_RATE 9600

  #define DELAI_STEP 2

  #define PIN_MOTEUR_GAUCHE 0x40 // pin 12
  #define PIN_MOTEUR_DROIT 0x20 // pin 11
  

  #define CPU_FREQ 16000000L
  

  //gestion des moteurs
  void init_pins(void){

      DDRB = PIN_MOTEUR_GAUCHE | PIN_MOTEUR_DROIT;
  }
  

  void pas_moteur(int g, int d){
      if (g)
          PORTB |= PIN_MOTEUR_GAUCHE;
      if (d)
          PORTB |= PIN_MOTEUR_DROIT;
      _delay_ms(DELAI_STEP);
      if (g)
          PORTB &= ~PIN_MOTEUR_GAUCHE;
      if (d)
          PORTB &= ~PIN_MOTEUR_DROIT;
      _delay_ms(DELAI_STEP);

  }
  
  //gestion de la liaison serie
  void init_serial(int speed){
      UBRR0 = CPU_FREQ / (((unsigned long int) speed) << 4) - 1; //Set baud rate
      UCSR0B = (1 << TXEN0 | 1 << RXEN0); //Enable transmitter & receiver
      UCSR0C = (1 << UCSZ01 | 1 << UCSZ00); //Set 8 bits character and 1 stop bit
      UCSR0A &= ~(1 << U2X0); //Set off UART baud doubler
  }
  
  void send_serial(unsigned char c){
      loop_until_bit_is_set(UCSR0A, UDRE0);
      UDR0 = c;
  }
  
  unsigned char get_serial(void){
      loop_until_bit_is_set(UCSR0A, RXC0);
      return UDR0;
  }
  
  int main(void){
      init_pins();
      init_serial(SERIAL_BAUDE_RATE);
  
      while(1){
          unsigned char deltaL1 = get_serial();
          unsigned char deltaL2 = get_serial();
          unsigned char deltaR1 = get_serial();
          unsigned char deltaR2 = get_serial();

  
  
  	send_serial('a');

          
          // conversion 2x8 bits => 16 bits

          int deltaL = (deltaL1 << 8) + deltaL2;
          int deltaR = (deltaR1 << 8) + deltaR2;

          
          int deltaMax = deltaL > deltaR ? deltaL : deltaR;
          for(int i=0; i<deltaMax; i++){

              if(deltaL > i && deltaR > i)
                  pas_moteur(1, 1);
              else if(deltaL > i)
                  pas_moteur(1, 0);
              else if(deltaR > i)
                  pas_moteur(0, 1);

          }

  	send_serial('b');

  	send_serial(0x01);

      }
      return 0;
  }