Does anyone know what makes this compatible with Arduino sketches? I suspect that the Arduino sketch has to target the Duo and perhaps the M0 and M3 share the Thumb-2 instruction set, but the M0 uses a "subset" of that instruction set. So I am wondering how compatibility is guaranteed. If they said that the M3 would run code target to the M0 I would say that makes sense, but I'm not so sure about the reverse.