Here’s an application note from Atmel: ASF – USB Composite Device (PDF!)
The aim of this document is to provide an easy way to integrate a USB composite device application on a new or existing project.
This document is associated to USB device class Atmel® application notes
AVR4903 to AVR4909.
ASF is a major pain in the *ss when it comes to modifying the base examples :/
Is there some compelling reason to use the Atmel framework over LUFA?
nope.
Advertising USB by using a picture of a RS-232 port. Makes sense.
I still prefer RS-232, I don’t have to pay for the privilege of a combination of a couple of bytes for the VID/PID. I also don’t need a complicated stack to use it. Rant over.