// This code example shows the set 
// of steps to follow before attaching the
// device on the bus. It is assumed that the
// device layer is already initialized.

USB_DEVICE_HANDLE usbDeviceHandle;

// Get an handle to the USB device layer.
usbDeviceHandle = USB_DEVICE_Open( USB_DEVICE_INDEX_0,
                                                  DRV_IO_INTENT_READWRITE );

if(USB_DEVICE_HANDLE_INVALID == usbDeviceHandle)
{
    // Failed to open handle.
    // Handle error.
}

// Register an event handler call back function with device layer
// so that we are ready to receive events when the device is 
// attached to the bus.

USB_DEVICE_EventHandlerSet(usbDeviceHandle, APP_USBDeviceEventHandler, NULL);

// Now, connect device to USB
USB_DEVICE_Attach(usbDeviceHandle);