Best Practice for determining if a USB serial device is still valid.

lev0207 · 03-01-2012, 05:39 PM

I have a micro-controller board connected to a home server computer (Ubuntu Linux 10.04) via USB. The board appears as a serial device (i.e. ttyUSB000). If the USB cable is disconnected the lock on the device remains and the process controlling it still thinks the device is there. When the cable is reconnected the device will appear as a different device (i.e. ttyUSB001). What is the best way for a process to determine if this has happened and find the new device name. I am using Java to program the process. Everything works fine but If I start doing some cable switching then I lose contact with the device. I assume that I know the device name and would also like to know if there is a better way of finding the device.

Thanks, no hurry,
Ernie

aus9 · 03-01-2012, 07:10 PM

have you considered creating an udev rule for the device.

consider this
http://hackaday.com/2009/09/18/how-to-write-udev-rules/

---------- Post added 02-03-12 at 08:10 ----------

have you considered creating an udev rule for the device.

consider this
http://hackaday.com/2009/09/18/how-to-write-udev-rules/

david1941 · 03-01-2012, 07:13 PM

What is the output from: lsusb ?

lev0207 · 03-02-2012, 07:54 AM

Aus9,

Udev rules might be at least a part of the answer. At least I should be able to determine the behaviour of the device if I can't communicate with it.

david1941,

I'm not sure that I want to be using lsusb from within my Java program. I could do that, but I'm not sure what value it would give me. Here is the specific lsusb line for this device.

Bus 001 Device 015: ID 16c0:0483 VOTI

Remember that I'm using it as a serial device ttyUSB000.

Thanks again
Ernie

david1941 · 03-02-2012, 09:24 AM

I don't know if it does help but I had a similar problem with the device changing on my scanner and set this up years ago and it still works:

Code:

# Determine scanning device - Epsom Prefection 640U attached (we hope)
DEVBUS=`/sbin/lsusb |grep Epson|cut -d " " -f2`
DEVDEV=`/sbin/lsusb |grep Epson|cut -d " " -f4`
DEVDEV=`echo $DEVDEV |sed s/://`
SANE_DEFAULT_DEVICE="epson:libusb:$DEVBUS:$DEVDEV"
[ -z "$DEVDEV" ] && SANE_DEFAULT_DEVICE=""
# The above discovers the usb device.  If power has cycled on the scanner, 
# the usb port changes, therefore using the environment doesn't always work. 

[ -n $SANE_DEFAULT_DEVICE ] || (echo "Cannot find the scanner!" && exit 1)

lev0207 · 03-03-2012, 08:09 AM

david1941

Excellent stuff. Thanks for you help. I'm not sure yet exactly what I'm going to do but it appears that I now have a couple of solutions.

Thanks again,
Ernie

lev0207 · 03-06-2012, 08:16 AM

I consider my question resolved at this point but I don't know how to make that indication.