Sometimes, whether intentionally (you want to “be” a different USB device) or unintentionally (your board is bricked), you want to replace the firmware on the little atmega usb chip used on the Arduino Uno. Unfortunately, most of the instructions out there are for the Uno R2 or earlier: the R3 has a slightly different chip. Adding to the trouble, the Linux/Mac tool for doing this operation (a “DFU upload”) has different USB product IDs than expected. So, here’s the differences from the earlier Uno (with ATMEGA8u2) to the latest R3 (with ATMEGA16u2):
- The dfu-programmer command line should contain at90usb162 instead of at90usb82.
- If the version of the dfu-programmer you’re using (which includes the latest SVN as of this posting) doesn’t recognize it, you’ll want to get the latest source code and apply this patch, which adds a different device name (at90usb162unor3 instead of at90usb162) that uses 0x2FEF as the product ID. (Thanks to http://forums.adafruit.com/viewtopic.php?f=25&t=25146 for the tip which led me to create the fix.) I opted to add a new device type, rather than change the existing one, in case someone actually takes the patch upstream and if the original product ID is correct for some devices, just not our Arduinos.
- I used the Arduino-COMBINED-dfu-usbserial-atmega16u2-Uno-Rev3.hex firmware file and had to pass the –suppress-bootloader-mem flag to the dfu-programmer flash command for it to work.