I'm using a MicroBlaze in an FPGA to do a USB audio gizmo. I need the FPGA to handle multiple I2S and TDM streams and interleave them into and deinterleave out of DMA buffers.

A very important point to consider: If you want to take advantage of High-Speed USB 2.0, then you must use USB Audio Class 2.0. (Class specifications are separate from the main USB spec, and when USB went to 2.0, many classes did not change and as such remained at whatever revision they were at.) Audio Class 1.0 does not support high speed, and there are some interesting changes in AC 2.0 (notably in the clock descriptors).

And of course there is a huge gotcha: AFAIK, Windows up to and including Vista DO NOT have built in class support for Audio Class 2.0. (Mac OS X 10.5 does.) So you will need to write a Windows device driver if you wish to support high-speed operation.

Of course you are still able to do a Full Speed USB 2.0 audio device using Audio Class 1.0.

Finally, regarding general porting from TAS1020: a lot of your firmware for that device deals with its particular hardware set, including the clock generation logic and the DMA buffering. Unless you're replicating that hardware, a lot of the firmware isn't portable to another platform. Also the TAS1020 handles a lot of bus transactions in its built-in firmware (unlike TUSB3200, where you had to do it yourself) so your firmware is probably little more than calling the appropriate handler.

Good luck,
-a