This is the development thread for Team Arduino, which will be taking my Arduino port for the SAM3S, bringing it up to the latest Arduino version, and pushing changes to the main tree so that Flutter's CPU (and perhaps many others) are officially supported by the main Arduino codebase.
Arduino has been selling one ARM-based board for several years, the Arduino Due. Flutter's CPU (SAM3S1A) is the baby brother to the processor in the Due (SAM3X8E) and has the same processor core. This means most code for the Due already mostly works on Flutter, so there are some minor changes. To our great fortune, Arduino used Atmel standard libraries for most of their Due support, and the Arduino codebase actually included the Atmel libraries for our CPU as well as the one used in the Due. This meant most of the code was already there, and the necessary makefiles and preprocessor directives were all that were needed to port Arduino to Flutter's CPU. I got Flutter working with Arduino on linux last year, and have been using it ever since (It's really nice!). We just need to clean that up and move the changes to the latest Arduino version.
Take my Arduino port. Do a Diff against the unmodified copy of that Arduino version to see my changes. Then take those changes and generalize them so they do not break support for other platforms (some of my changes broke DUE support by commenting things out instead of using #ifdef). Then move these changes to the latest version of Arduino.
Code is here: