How to find out which USB-RS232 device is on which tty?

Question

I have two different USB devices based on the same USB-RS232 chips. When I plug those in the USB they are mounted to /dev/ttyUSB0...3

My problem is how, inside a script, I can find out which one is on what tty?

Using lsusb I can differentiate them:

$> lsusb | grep 0403:f850
Bus 004 Device 002: ID 0403:f850 Future Technology Devices International, Ltd
$> lsusb | grep 0403:6001
Bus 004 Device 003: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC

And using dmesg I can tell where they were mounted:

$> dmesg | grep 'FTDI USB Serial Device converter now attached'
[36051.393350] usb 4-2: FTDI USB Serial Device converter now attached to ttyUSB1
[36061.823513] usb 4-1: FTDI USB Serial Device converter now attached to ttyUSB0

But "usb 4-1" does not seem to correspond to "Bus 004 Device 002".

Can I assume that "Bus 004 Device 001" will always be an "USB root hub" and thus dmesg will count from 1 onwards and lsusb from 2 onwards?

Or do you have another suggestion on how to correlate device ID to mount point (inside a script)?

I'm using Ubuntu 10.04 LTS.

Answer 1

Find more info using sysfs:

$ ls /sys/bus/usb-serial/devices/ -ltrah

lrwxrwxrwx 1 root root 0 2012-02-07 22:17 ttyUSB0 -> ../../../devices/pci0000:00/0000:00:0f.4/usb2/2-2/2-2:1.0/ttyUSB0

$ ls -ltrad /sys//devices/pci0000:00/0000:00:0f.4/usb2/2-2/2-2:1.0/ttyUSB0
drwxr-xr-x 4 root root 0 2012-02-07 22:17 /sys//devices/pci0000:00/0000:00:0f.4/usb2/2-2/2-2:1.0/ttyUSB0

$ ls -ltrad /dev/ttyUSB0 
crw-rw---- 1 root dialout 188, 0 2012-02-01 00:17 /dev/ttyUSB0

Of course, the linked devices/... node contains a lot of information

Adding information based on the OP's comment:

The device number keeps growing if devices are removed/inserted. lsusb -t can be used to correlate the device numbers with usb bus/port.

Then, 'lsusb -d devID' can determine what device is on which port. Finally 'ls /sys/bus/usb-serial/devices/ -ltrah' will list (by bus/port) where it was mounted.

Not very convenient, but it 'works'

Answer 2

You can use udev to assign a stable symbolic link to each FTDI dongle. Use device and vendor to match the type, and then the serial number for the specific device. Then use the symbolic link in the script.

I named my dongles ttyFTDI0 etc., and wrote the numbers on the dongles with a marker:

$ cat /etc/udev/ftdi.rules 
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="FTDEN97D", SYMLINK+="ttyFTDI0"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="A600b30P", SYMLINK+="ttyFTDI1"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="A600bexU", SYMLINK+="ttyFTDI2"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="FTFMSA54", SYMLINK+="ttyFTDI3"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="FTFMUW4A", SYMLINK+="ttyFTDI4"

Answer 3

This one-liner udev rule will give a fixed name (e.g. /dev/ttyUSB_A9YL5BJJ) based on serial number for any device with vendor/product ids as given.

Put this into a udev rules file e.g. /etc/udev/rules.d/60-ftdi-serial-names.rules

SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ENV{ID_SERIAL_SHORT}=="?*", SYMLINK+="ttyUSB_%E{ID_SERIAL_SHORT}"