This is an old thread that also pertains to creating udev rules for 
various plug and play devices, particularly USB.  Everything has been 
working nicely for a few months under Ubuntu 10.04 but today for the 
first time I tried to set up a pair of udev rules for two devices of the 
same type that differ only in their serial numbers

The two devices are a pair of USB2Dynamixel controllers and the rules I 
tried are:

# The USB2Dynamixel on Pi Robot controlling AX-12 servos
SUBSYSTEMS=="usb", KERNEL=="ttyUSB[0-9]*", ATTRS{manufacturer}=="FTDI",
ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A1001a6n",
SYMLINK+="usb2dynamixel12"

# The other USB2Dynamixel on Pi Robot controlling RX-24 servos
SUBSYSTEMS=="usb", KERNEL=="ttyUSB[0-9]*", ATTRS{manufacturer}=="FTDI",
ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A600cB3f",
SYMLINK+="usb2dynamixel24"

The trouble is that whenever I plug in either controller, *both* devices 
get created (/dev/usb2dynamixel12 and /dev/usb2dynamixel24) and they 
both point to the same /dev/ttyUSB device which is /dev/ttyUSB0 if only 
one controller is plugged in and /dev/ttyUSB1 if they are both plugged in.

When I run

$ udevadm info -q all --attribute-walk -n /dev/ttyUSB0

when one or the other controller is plugged in, then diff the results I get:

54c54
<     ATTRS{devnum}=="7"
---
 >     ATTRS{devnum}=="8"
61c61
<     ATTRS{serial}=="A1001a6n"
---
 >     ATTRS{serial}=="A600cB3f"
72c72
<     ATTRS{urbnum}=="85"
---
 >     ATTRS{urbnum}=="113"
99c99
<     ATTRS{urbnum}=="57"
---
 >     ATTRS{urbnum}=="62"

so you can see my serial numbers are correct.  Does anyone know how to 
handle this situation?

Thanks!
patrick

http://www.pirobot.org

P.S. I have attached the entire output from udevadm when one of the 
controllers is plugged in.