Software only USB implementation for ARM-M0/M0+?
Here's a new M0+ implementation comparable to V-USB
https://github.com/xobs/grainuum
Interesting 33c3 video explaining as well: https://youtu.be/GFY_A3jcI28
Still pretty fresh and prob not as stable as V-USB but sounds promising.  Curious how vital the 2 stage pipeline of the M0+ really is as would be nice to implement this on M0.
Doesn't sound like he's so tight that he can't afford one more cycle with the 3 stage pipeline.  I think the biggest issue will be M0's lack of single cycle I/O ports which is an optional feature of the M0+.  But he makes it sound like the pipeline is the real benefit of M0+.