Stratix-IV DXAUI

Hi,

we are going to use a Stratix-IV EP4SGX230KF40C device, and I want to use the 20GbE DXAUI core.
Two questions:
- what is the required frequency of the external reference clock? Still 156.25MHz or 312.5MHz?
- how do I connect the clock signals on the XGMII-side? There is a new signal, called "tx_clk312_5", that
there is no documentation on how to use.

Thanks a lot