ROVER shield

/*To control the rover, copy and paste the code below into the Arduino software*/
int E1 = 6; //M1 Speed Control
int E2 = 5; //M2 Speed Control
int M1 = 8; //M1 Direction Control
int M2 = 7; //M2 Direction Control

void setup(void)
{
  int i;
  for(i=5;i<=8;i++)
  pinMode(i, OUTPUT);
  Serial.begin(9600); // Therefore if you send serial commands, they should be at 9600 baud, Xon/Xoff
}

void loop(void)
{
  while (Serial.available() < 1) {} // Wait until a character is received
  char val = Serial.read();
  int leftspeed = 255; //255 is maximum speed
  int rightspeed = 255;
  switch(val) // Perform an action depending on the command
  {
    case 'w'://Move Forward
      forward (leftspeed,rightspeed);
      break;
    case 's'://Move Backwards
      reverse (leftspeed,rightspeed);
      break;
    case 'a'://Turn Left
      left (leftspeed,rightspeed);
      break;
    case 'd'://Turn Right
      right (leftspeed,rightspeed);
      break;
    default:
      stop();
      break;
    }
}
void stop(void) //Stop
{
  digitalWrite(E1,LOW);
  digitalWrite(E2,LOW);
}
void forward(char a,char b)
{
  analogWrite (E1,a);
  digitalWrite(M1,LOW);
  analogWrite (E2,b);
  digitalWrite(M2,LOW);
}
void reverse (char a,char b)
{
  analogWrite (E1,a);
  digitalWrite(M1,HIGH);
  analogWrite (E2,b);
  digitalWrite(M2,HIGH);
}
void left (char a,char b)
{
  analogWrite (E1,a);
  digitalWrite(M1,HIGH);
  analogWrite (E2,b);
  digitalWrite(M2,LOW);
}
void right (char a,char b)
{
  analogWrite (E1,a);
  digitalWrite(M1,LOW);
  analogWrite (E2,b);
  digitalWrite(M2,HIGH);
}