usbd_set_config_no vs. usbd_set_config_index

[Andriy Gapon]

I am curious about a difference between usbd_set_config_no and
usbd_set_config_index. My reason is such: I am trying to use
palm/uppc-kmod to talk to my pocket pc device via usb. When I used the
port in its original shape it gave me the following error each time I
plugged the device:
kernel: ucom0: failed to set configuration, err=STALLED
kernel: device_attach: ucom0 attach returned 6

Then, to mimic some other driver I simply changed
usbd_set_config_index() to usbd_set_config_no() in the code, and voila:
kernel: ucom0: <Windows CE Device> ASUS ASUS Windows Mobile Device, rev
2.00/0.00, addr 3 (rt)

I am now trying to get synce to actually work.
But I am really curious what my change really did, and I am totally
ignorant about our usb code.
BTW:
FreeBSD 6.2-RELEASE-p3 amd64

Thank you in advance for my education.

-- 
Andriy Gapon