USB Enumerator and class drivers

Currently to start a usb class driver I run the appropriate devu-* class
driver for a device. which monitors for connection and disconnection of
that type of device. The QNX man pages refer to a USB enumerator looking in
a configuration manager’s database and starting the appropriate driver. So
say for example I plugged in a USB printer then the USB enumerator would
start devu-prn. I can’t seem to find anything that describes how to do this
does anyone have any pointers.