There may be hope for USB just yet...

In talking with one of the Raspberry Pi guys, I've learned that the USB performance problems I am seeing are related to the FTDI chip I chose to put on the Dexter board.  This means that it is possible that using another vendor's chip may solve this issue.

He says: "Looking at your post I see you were hitting the high CPU issue, which is inevitable with the FTDI serial adaptor. Was this the only issue?

I'm pretty sure that Gordon has a non-FTDI serial apator that doesn't suffer the high CPU effect. I'll try and find out exactly what is was."

What this means is that for rev2 of the Dexter board, the only way to use it with a Raspberry Pi will be to hook into the pins on the pi itself using the same method I used (which is not the most convenient but it works!).  I will probably post the steps I took for this method later, but using a PC to test still works fine so no one should be blocked in their testing :)

For the next (final?) revision of the Dexter PCB, hopefully another USB<->serial chip will surface so that the USB port can be used with the Raspberry Pi.  The good news is that the rev2 Dexter board is still and will be very useful for testing going forward since it works fine with a PC and I still have a lot of firmware code to write for it.