// https://forum.arduino.cc/t/sscanf-bug-what-i-am-doing-wrong/1046254

const int rs485dir = 13 ;


uint32_t myBeginTime ;
uint32_t myEndTime ;
uint32_t bufferEmptyTime ;

void setup()
{
  Serial.begin(9600) ;
  Serial.println("block no block\n");

  pinMode(rs485dir, OUTPUT) ;

myBeginTime = millis();

  sendBlockingMessage() ;

myEndTime = millis();

   Serial.print( "                          my blocking time measurment : ");
   Serial.println(myEndTime - myBeginTime ) ; 

  delay(500);

myBeginTime = millis();

  sendNonBlockingMessage() ;

myEndTime = millis();
}

void sendBlockingMessage()
{
   for( int i = 0 ; i < 25 ; i ++ )
   {
       Serial.write('X') ;
   }
   Serial.println() ;
   Serial.flush() ;
}

void sendNonBlockingMessage()
{
   for( int i = 0 ; i < 25 ; i ++ )
   {
       Serial.write('X') ;// send 25x
   }
   Serial.println() ;

  digitalWrite(rs485dir, HIGH ) ;
}

void loop()
{  
  if( Serial.availableForWrite() == 63 
  && digitalRead( rs485dir ) )
  {
    bufferEmptyTime = millis() ;

    Serial.print( "                          my non blocking time measurment : ");
    Serial.println(myEndTime - myBeginTime ) ; 


    Serial.print("buffer is empty after: ");
    Serial.println(bufferEmptyTime - myBeginTime ) ;
    digitalWrite( rs485dir, LOW) ;
  }
}