FT2232H in Sync FIFO Mode - TXE# stuck high

For big transfer buffer size and data latency doesn't affect speed.

For small transfer I set latency to 1 ms and use SIWO. Key to improve performance is to make less bigger Write call to use less USB microframe.

I reached 50 MB/S in read and 14 MB/S in read (see last image into http://electro-logic.blogspot.it/2014/02/fpga-comunicazione-ad-alta-velocita_16.html)