How to differentiate between 2 Micros on Linux

Question

I have 2 Arduino Micro based devices that I want to use on my Ubuntu Linux machine. I need them to have unique serial ports. Unfortunately, both have the same serial number which makes identification through udev rules difficult (if not impossible).

This is the serial number that I get for both:

$ udevadm info -a -p  $(udevadm info -q path -n /dev/ttyACM0) | grep -i serial
  ATTRS{serial}=="0000:00:14.0"

Is there any way to manually set the serial number on an Arduino Micro? Or is there any other unique identifying properties I can use for udev rules?

Typically, I do something like this in my /etc/udev/rules.d/99-usb-serial.rules file:

SUBSYSTEM=="tty", ATTRS{product}=="Arduino Uno", ATTRS{serial}=="64936333936351911191", SYMLINK+="MyDevice"

Side note: I also have a Due, that has the same serial number as the Micros, but since ATTRS{product} is different, I can differentiate it.

Answer 1

The USB VID, PID and Serial Number are all programmed into the chip when you upload your sketch. The VID and PID are tied to the board, and the serial number is always the same regardless of which board.

So no matter which board you program it will get the same details as any other board of the same kind.

There's no option to change the serial number (there is, IIRC, actually no serial number defined) but the VID and PID are provided as a pair of macros on the compilation command line: USB_VID and USB_PID.

So you could (cheakily) create a new board definition (based on the existing Micro one) that is "The other Micro" and provide a different (unofficial) PID to that board. You can then differentiate the two boards in udev using the VID/PID combination.

Of course, you have to then ensure that you have the right board selected when you program them, and the act of entering the bootloader on the "other" board would revert back to the old PID which is programmed into the bootloader, but I'm sure you can cope with that.

Answer 2

That "0000:00:14.0" isn't the serial number for the Arduino: udevadm is printing info for more than one device, and that's for the USB controller chip.

Arduinos built on the ATMEGA32U4 don't get a serial number: I have some Leonardos giving me the same problem you're having. When the bootloader was originally designed, the programmer didn't have it report one. I found a modified bootloader that does, but I haven't tried it yet: http://forum.arduino.cc/index.php?topic=503703.0

Genuine Arduinos with an FTDI chip report unique serial numbers. Some of the knock-offs either don't set it in the chip, or may set it to some non-unique number(skipping that step to save a few cents of manufacturing cost). Ones that use a 16U2 chip for the USB interface (like the Uno R3) are supposed to get a unique serial number. The Chinese ones I just bought did, but it's possible that other makers of them are cutting corners like some users of FTDI chips do.

Arduinos that use the Chinese CH340 USB chip also don't report a serial number: the chip doesn't support it. I think that's also true for the CP2102, but I'm not certain.

You may be able to fix the problem with that modified bootloader (I hope so: I have half-a-dozen Leonardos, and it's a hassle anytime I have more than one connected simultaneously. Fortunately, I don't normally use them as "PC peripherals"). Or you could buy another of the "tiny" Arduinos with a 328P that uses a USB-to-serial chip, and base the udev rules on VID and PID to distinguish them.