I have a question that I need to answer. I have a USB device which I installed a mass storage class. When I connect the device on the computer, it detects the drive and I can access to driver correctly. I don't know how to handle the USB interface when the device is busy to do an other critical task. For example, I don't want to copy a file in the drive if the device is presently busy in a critical task. Actually, I disabled the USB interrupts in the lpc microcontroller during the critical task... but after 1 or 2 minutes, the computer will not recognize the drive and I need to do unplug/replug the usb device to continue to work on the PC. So It's not a good practice to disable USB interrupts...