Hello,
I’m just wondering… Why does the Ft have its own 100 MHz oscillator instead of using the clock from the Au/Cu that is available on bank D?
Thanks 
This is because the FT600 provides the bus clock. There isn’t another 100MHz oscillator. The 100MHz comes from the FT600 directly (a PLL inside it generages it from the 30MHz crystal). See the data sheet for more info.
As for why the FT600 provides the bus clock instead of relying on the other device to provide one, you’ll have to ask FTDI 
Oooh, ok, I thougt it was a 100 MHz oscillator because it’s what we get on the pin.
But my question was actually “Why don’t we clock the FTDI from the main clock?”, and the answer is probably that generating a reliable 30 MHz clock from the FPGA would be touchy?
Well the answer to that is because FTDI said not to. See page 18.
The FT60x device requires an external clock source to control the internal circuitry.
The recommended parameters for the crystal are: 30MHz ±20ppm Crystal 18pF 50 Ohm -40°C ~ 85°C.
The crystal should be connected across the XI and XO pins.
Note: It is not possible to replace the crystal with an oscillator or other clock source by tying XO to GND.
Oh it’s a crystal, so they have an internal oscillator, that explains why XD
So it’s build to have make it’s own clock
Probably because this chip is often used as primary interface and/or monitor so they probably want it to work as independantly as possible.
Beeing able to clock it would have saved some synchronization circuits for us 