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Configure USB for Fixed Name

Complex Rule

In Linux one of the issues using a USB to serial port converter is the name can change. The sequence of plugging in USB devices determines the names. There is a system called udev that determines the names. It allows rules to be created that will provide a fixed name for devices. It is a challenge to create the rules. Here are some basics but they might not handle all situation, e.g. two serial devices from the same vendor.

First you need to determine the vendor and product identifiers for the device. With it plugged in run:

lsusb

On my system the response is:

Bus 002 Device 002: ID 8087:8000 Intel Corp. 
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 8087:8008 Intel Corp. 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 036: ID 10c4:ea60 Cygnal Integrated Products, Inc. CP210x UART Bridge / myAVR mySmartUSB light
Bus 003 Device 002: ID 047d:2048 Kensington Orbit Trackball with Scroll Ring
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

What you need to find is the entry that is your serial device. If you can't identify it unplug the device and run the command again. The one that is missing is your device.

The identifies follow the ID on the line for your device. Mine IDs are 10c4 and ea60, for vendor and product. Use these exactly as the appear keeping the case of the text exactly the same, i.e. vendor 10c4 is not the same as 10C4.

Using your IDs create a file 80-rvr.rules containing:

ACTION=="add", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", MODE="0666", SYMLINK+="rvr"

Then copy the file to the etc/udev/rules.d/ and load the rule using the commands:

    sudo cp 80-rvr.rules /etc/udev/rules.d/
    sudo udevadm control --reload-rules && sudo udevadm trigger

To check this worked look at the /dev directory where all devices are listed using:

ll /dev

In the directory you should see:

lrwxrwxrwx   1 root root           7 Nov  8 21:14 rvr -> ttyUSB0

The end of the line may be any of the tty* devices depending on your system and the USB to serial converter being used. Some will be ttyUSB as shown, some ttyACM, and possibly others.

** Additional Information

You can get more information about your device with the command:

sudo udevadm info -q all -n ttyUSB0

Complex Rule

SUBSYSTEM=="usb", ATTRS{idVendor}=="1ffb", MODE="0666"
KERNEL=="ttyACM*", SUBSYSTEMS=="usb", ACTION=="add", ATTRS{idVendor}=="1ffb", ATTRS{idProduct}=="008[0-f]", MODE="0666", PROGRAM="/bin/bash -c '/bin/echo %p | /bin/grep -c :1.0/tty'", RESULT=="1", SYMLINK+="polulu_servo_serial_$attr{serial}", GROUP="dialout"
KERNEL=="ttyACM*", SUBSYSTEMS=="usb", ACTION=="add", ATTRS{idVendor}=="1ffb", ATTRS{idProduct}=="008[0-f]", MODE="0666", PROGRAM="/bin/bash -c '/bin/echo %p | /bin/grep -c :1.2/tty'", RESULT=="1", SYMLINK+="polulu_servo_ttl_$attr{serial}", GROUP="dialout"
KERNEL=="ttyACM*", SUBSYSTEMS=="usb", ACTION=="add", ATTRS{idVendor}=="1ffb", ATTRS{idProduct}=="009[0-f]", MODE="0666", PROGRAM="/bin/bash -c '/bin/echo %p | /bin/grep -c :1.0/tty'", RESULT=="1", SYMLINK+="polulu_smc_$attr{serial}", GROUP="dialout"