Hey prifken,
Have you taken a look at the example code that Andy Mark posted? It uses I2C to communicate between the roboRIO and the RIOduino to control a touch display.
The example can be found on the "Files & Documents" tab of the RIOduino product page:
http://www.andymark.com/product-p/am-2999.htm
At first glance I noticed one thing about your LabVIEW code. I think it is recommended to put the
I2C Open code in
Begin.vi rather than in
Periodic Tasks.vi
On the Arduino side of things it may be better to separate out your I2C receiving and sending operations into two different handlers. It looks like you're trying to send "hello" out as you're reading the receive buffer.
I hope the example code will help. Let me know if you have any further questions!
-David