TUSB7320 Crystal Oscillation

Hi, we are using the TUSB7320 USB 3.0 Host in a prototype design. The chip connects to a 
PCIe Gen 1 host (chipset ICH8M) on our board. When booting both Ubuntu 11.10 and Windows 
XP, the OS can see the TI PCIe target device. However, our crystal circuit does not oscillate ever. 

Our design is closely based on the TUSB7320 EVM.  A 1 MOHM resistor is placed across XO 
and XI. 18 pF capacitors are placed between XO, XI and VSSOSC. We are not using the optional 
EEPROM and both SDA and SCL are grounded. The FREQSEL pin is grounded. We have a clean 
deassertion of RST# after power supplies are stable. PCIe Ref Clk is stable before the PCI Reset 
is deasserted by the host. 

In addition, we have tested the same crystal used in the TUSB7320 EVM reference design as well 
as a slightly different one (Abracon ABLS-48.00MHZ-B2-T) on multiple boards ruling out faulty crystals.

So, we are wondering if the crystal is supposed to be oscillating when first powered (as we suspect) or 
only when it sees a USB device on the hub?

Any help would be appreciated.

Thanks, 
Patrick