For the final firmware, I've extracted all the code that controls the buttons and leds into a library to make it more tidy, all of this is in a class called SugarCube. I was inspired by the work I've been doing on the Instructables iOS app, and wrote the event handling pieces of the code so that they work in a similar way that an iPhone deals with touch and other gestural events. Basically I created a set of methods that each app can subscribe to, things like "deviceWasShaken" or "buttonPressed". When the SugarCube class detects one of these events, it tells the current app to execute the corresponding method. If you're interested in seeing an example of this structure in action, check out SimpleMIDIKeyboard.cpp, it shows how few lines of code are needed to wire up all the button and analog controls to MIDI outputs. I hope to eventually write out a little more complete documentation for how to write your own apps based on this framework, please let me know if there is interest. This is by far my biggest piece of C++ code, and I am by no means an expert in C++, I'd love to hear an expert's thoughts on how I did!

https://github.com/amandaghassaei/Sugarcube-Arduino-Library