I'm trying to connect two Arduino microcontrollers to my laptop running Debian Stretch, but without success. Connecting a single board works fine. The problem seems to be that both Arduinos are assigned to the same serial port (for example /dev/ttyACM1), and then one of the boards gets disconnected. Here is the output of dmesg when I connect the first board via USB:
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[331661.246877] usb 2-1: new full-speed USB device number 93 using xhci_hcd
[331661.397748] usb 2-1: New USB device found, idVendor=2341, idProduct=0242
[331661.397753] usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=220
[331661.397755] usb 2-1: Product: Genuino Mega 2560
[331661.397757] usb 2-1: Manufacturer: Arduino LLC (www.arduino.cc)
[331661.397759] usb 2-1: SerialNumber: 55434343633351501181
[331661.398492] cdc_acm 2-1:1.0: ttyACM1: USB ACM device
And this is what happens when I connect the second board:
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[331676.860957] usb 2-1: USB disconnect, device number 93
[331677.082844] usb usb3-port1: over-current condition
[331678.074958] usb 2-2: new full-speed USB device number 94 using xhci_hcd
[331678.225561] usb 2-2: New USB device found, idVendor=2341, idProduct=0242
[331678.225566] usb 2-2: New USB device strings: Mfr=1, Product=2, SerialNumber=220
[331678.225569] usb 2-2: Product: Genuino Mega 2560
[331678.225572] usb 2-2: Manufacturer: Arduino LLC (www.arduino.cc)
[331678.225575] usb 2-2: SerialNumber: 5543434363335150C0B0
[331678.226313] cdc_acm 2-2:1.0: ttyACM1: USB ACM device
The strange thing is that connecting two boards to the same computer worked fine when I last tested it about a year ago. At that time, one Arduino was automatically assigned to ttyACM0 and the second to ttyACM1. Maybe the issue was introduced through a kernel update? I'm running kernel 4.14 from stretch-backports, because the default kernel in Stretch (4.9) causes graphical artifacts and system crashes with my hardware.
Any idea how to solve or debug this? I've already spent hours googling, but to no avail. If you'd like to have additional information about my system, let me know.