I am not unexperienced with AVRs. Owning a bunch of SPI programmers and a JTAGICE3.
The first thing I realized was that the easy to use development environment only supports one source file. Well. And it’s rather minimalistic. I switched to real makefiles and Eclipse.
Then I found out that the standard libraries are mainly supporting a linear synchronous programming model without fancy timers and interrupt handlers. I did start to write my own libraries in plain C.
When I tried to plug an interrupt routine into USART1 I got errors because the default libraries did occupy all serial interrupts, not only the one of USART0 used for the USB connection. That’s understandable because the AVR isn’t made for hardware abstraction and dynamic configuration. I did remove all the Arduino C++ code and recycled an existing library for the console I/O.
Now I am happy with an Arduino using purely the hardware. A really nice piece. I bought a second one.