Driver software for USB OTG device mode interface on DE0-nano-SoC?

We would like to transfer data from a DE0-nano-SoC board to a linux host using the high-speed USB OTG port on the DE0. We need to get about 2 MB/s. At the host end, the libusb library seems to provide good user-level support, as long as the far end will act like a proper USB "device". At the DE0, we would be running linux, but the 3300 interface chip seems to be a very low-level physical interface (ULPI?). Is there software available that will implement the device or "gadget" side USB protocol for this interface, and on top of that something that would provide a user-level interface (since libusb apparently doesn't support the device end)?