[PLUG] USB Serial Port Adapters

Tim Wescott tim at wescottdesign.com
Mon Jun 20 14:34:40 PDT 2011

... and I figured out my terminal program.  It doesn't _see_ links, but 
it can _use_ them (and if I get my serial settings right, things even 
work! :) )

On 06/20/2011 01:33 PM, Tim Wescott wrote:
> Thanks.  This is exactly the guidance I was looking for.  My preferred
> terminal program doesn't seem to understand links to devices, but I'll cope.
> On 06/18/2011 09:49 AM, Jason Barnett wrote:
>> Here is a link that gives an example of this exact situation.  The example
>> shows using a FTDI chip and having the UDEV rule compare against the serial
>> number of the device so it should work for specific devices.
>> https://wiki.archlinux.org/index.php/Bus_pirate
>> Jason
>> On Fri, Jun 17, 2011 at 8:45 PM, Fred James<fredjame at fredjame.cnc.net>wrote:
>>> Jackman wrote:
>>>> Why can't udev rules be applied here?
>>>> On Fri, Jun 17, 2011 at 6:48 PM, Fred James<fredjame at fredjame.cnc.net>
>>> wrote:
>>>>> Tim Wescott wrote:
>>>>>> (omissions for brevity)
>>>>>>     I did an experiment: I started with my Fax
>>>>>> modem and the board I'm developing plugged in.  I did ls /dev/ttyU*.
>>>>>> Then I unplugged the development board and did ls again.  Then I
>>> plugged
>>>>>> in a debugger that has its own USB serial port adapter, and did ls
>>>>>> again.  Here's my results:
>>>>>> tim at servo:~$ ls /dev/ttyU*
>>>>>> /dev/ttyUSB0  /dev/ttyUSB1
>>>>>> tim at servo:~$ ls /dev/ttyU*
>>>>>> /dev/ttyUSB0
>>>>>> tim at servo:~$ ls /dev/ttyU*
>>>>>> /dev/ttyUSB0  /dev/ttyUSB1
>>>>>> What _did_ happen is that at different times the same device -- ttyUSB1
>>>>>> -- got mapped to different physical devices.  That is what I _do not_
>>>>>> want to happen.  What I want to happen is to plug in the development
>>>>>> board and have /dev/ttyUSBdevelop appear, and to plug in the debugger
>>>>>> and have /dev/ttyUSBdebug appear (or some similar me-defined mapping).
>>>>>> Different devices.  Different, _unique_, identifiers.
>>>>>> Otherwise, every time I plug a bunch of stuff in to the machine, I'm
>>>>>> going to have to do a bunch of hand work to figure out what ports map
>>> to
>>>>>> what devices at the moment.
>>>>> Tim Wescott
>>>>> Thought 1:  If you can use CLI (command line interface) to determine
>>>>> what you need to know, then a (BASH) script can be written to do that.
>>>>> Thought 2:  If a device can be identified (example: ttyUSB1 is the
>>>>> debugger), then it can be mounted to a directory (example: ~/debugger)
>>>>> Thought 3:  If 1 and if 2, then the two can be written together in a
>>> script.
>>>>> Does any of that help?
>>>>> Regards
>>>>> Fred James
>>> Jackman
>>> According to<http://reactivated.net/writing_udev_rules.html#about>, it
>>> can ...
>>> "
>>> udev rules are flexible and very powerful. Here are some of the things
>>> you can use rules to achieve:
>>>      * Rename a device node from the default name to something else
>>>      * Provide an alternative/persistent name for a device node by
>>>        creating a symbolic link to the default device node
>>>      * Name a device node based on the output of a program
>>>      * Change permissions and ownership of a device node
>>>      * Launch a script when a device node is created or deleted
>>>        (typically when a device is attached or unplugged)
>>>      * Rename network interfaces
>>> "
>>> Regards
>>> Fred James
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Tim Wescott
Wescott Design Services
Voice: 503-631-7815
Cell:  503-349-8432

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