Udoo uses serial bus for communication between processor and Arduino. As a heavy Udoo user (I am using Udoo with internal and external Arduinos attached with custom made shield), I wrote JSON-RPC server Arduino library for easy Master-Slave communication. Library contains MACRO based automation for super easy remote procedure definition. http://www.cloud-rocket.com/2014/03/ser ... r-arduino/ Enjoy, Meir Tseitlin
