USB Camera Driver

I’m jumping in on a project for the summer in which I’m supposed to be
tweaking a functional driver for a USB Logitech Quickcam 4000 webcam in
QNX; however I’m new to QNX and haven’t written a USB device driver before.
Unfortunately the current driver that was written last summer is not
working, and the author is stumped (he’s kinda new to both QNX and USB
drivers too). At the moment when we try to use to camera to capture images,
in are CBF the urb_len returned by urb_status() is constantly 0, which we’ve
assumed means there is no data in the urb’s buffer. Does anyone have any
ideas on what to check?