I'd try blinking the pin 13 LED in the Arduino sketch, whenever it successfully read a byte. That way, you'd know when the Arduino received something, although the RX light should flash to tell you that. Similarly, the TX light should flash when the Arduino sends data.
The TX and RX light on duration is pretty short, and easy to miss, so making the onboard LED light up for longer makes it easier to see.
The variable intr is already an int. There is no reason to explicitly cast an int to an int.