Feedback with embedded USB audio gadget

[David Jaffe]

I see that the USB Gadget has an explicit feedback node.   It seems to
deliver a constant (00 00 30 00) for a sample rate of 48kHz.    I see that
the value is initialized to a combination of the sample rate and the
"pitch", which appears to be a control of the driver.  Is the pitch plumbed
up to the user-level through alsa somehow (if so how)?    If not, is there
some ALSA layer that servos the pitch to keep the host clock and the
embedded clock synchronized?