I've been experimenting with a minimal USB stack based on the nonolith/Kevin Mehall one. I made a few fixes for XMEGA and successfully implemented a bootloader.
In benchmarks sending a 64 byte buffer via a 64 byte bulk endpoint, the maximum transfer rate is limited to 1.9Mb/sec. That's pretty far from the 12Mb bus speed. Okay, 12Mb includes all the protocol overhead, coding and the like, but I'm a little disappointed with 2Mb.
I did a similar experiment with the ASF stack and got 1.9Mb, the same.
Has anyone managed to get over 2Mb/sec from an XMEGA? I'm thinking that this might be the limit for the chip. Maybe ARM can go faster.