Board: Arduino Mega,
Problem is reproducible with the IDE running on a MAC (OS 10.7.5) and on a PC running 64 bit Win7
Subject sketch had previously uploaded and executed without a problem
Upload verbose error message says: avrdude: usbdev_open(): did not find any USB device "usb"
My design uses a daughter board connected to a variety of pins on the Mega board. I think the issue involves pin 31 which I am using as a digital input pin to measure the duration of 5 volt pulses. I mistakenly applied a pulse 12 volts below ground. After that, the Arduino froze (code execution stopped). After power cycling the boards (Arduino and daughter board) the Arduino did execute its previously loaded firmware image
The loader LED blinks when I reset the Arduino and it does execute the version of the firmware that was loaded in it prior to the "event". Have I fried the USB port on the Arduino? Is there a way to recover?