Associated constant in the API stacks: USB_XT_FREQ. (Not reported in the USB descriptors.)
This value must match the frequency of the crystal, resonator, or clock applied to the XT2 oscillator.
The API enables the XT2 oscillator when USB is active, and optionally disables it during USB suspend. It uses XT2 as a reference to the USB PLL.
XT2 needs one of these applied to it:
Many input frequencies are possible, allowing cost reduction: