RNode is controlled by a powerful ATmega1284p MCU, and is fully Arduino compatible. You can use this firmware, or it can be programmed any way you like, either from the Arduino IDE, or using any of the available tools for AVR development. This firmware can also be edited and compiled directly from the Arduino IDE.
For configuring an RNode with this firmware, please have a look at the [RNode Config Utility](https://github.com/markqvist/rnodeconfigutil).