Re: Linux USB serial questions

[Jeong Han Lee <jhlee@ibs.re.kr>]

Dear Mark,

There are three things I want to share. I think, you already know them, 
but just in case.


1) If an user is in the dialout group (uucp for RHEL, I guess), the user 
can read/write to a Serial Port.

  So I think, don't need to execute chmod o+rw /dev/ttyUSB0

2) Each device has its own unique name (usually by-id directories
   in /dev/  directory. If you type tree in /dev/, you will see many 
symlinks

  For example,

ctrluser@ctrlpc1:/dev/serial$ tree
.
├── by-id
│   └── usb-Arduino__www.arduino.cc__0043_A4139363931351B06171-if00 -> 
../../ttyACM0
└── by-path
    └── pci-0000:00:1d.0-usb-0:1.2:1.0 -> ../../ttyACM0

3) And  you can write your own symlink for any device, I didn't try it 
myself, but I think it can be used to fix your devices in their own 
symlinks.

  Please see 70-persistent-cd.rules for further reference. In my system,
----------------------------------------------------------------------
root@ctrlpc1:/etc/udev/rules.d# more 70-persistent-cd.rules
# This file was automatically generated by the /lib/udev/write_cd_rules
# program, run by the cd-aliases-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single
# line, and set the $GENERATED variable.

# CDDVDW_SH-216AB (pci-0000:00:1f.2-scsi-4:0:0:0)
SUBSYSTEM=="block", ENV{ID_CDROM}=="?*", 
ENV{ID_PATH}=="pci-0000:00:1f.2-scsi-4:0:0:0", SYMLINK+="cdrom", 
ENV{GENERATED}="1"
SUBSYSTEM=="block", ENV{ID_CDROM}=="?*", 
ENV{ID_PATH}=="pci-0000:00:1f.2-scsi-4:0:0:0", SYMLINK+="cdrw", 
ENV{GENERATED}="1"
SUBSYSTEM=="block", ENV{ID_CDROM}=="?*", 
ENV{ID_PATH}=="pci-0000:00:1f.2-scsi-4:0:0:0", SYMLINK+="dvd", 
ENV{GENERATED}="1"
SUBSYSTEM=="block", ENV{ID_CDROM}=="?*", 
ENV{ID_PATH}=="pci-0000:00:1f.2-scsi-4:0:0:0", SYMLINK+="dvdrw", 
ENV{GENERATED}="1"
--------------------------------------------------------------------
root@ctrlpc1:/dev# tree |grep "pci-0000:00:1f.2-scsi-4:0:0:0"
│   │   └── pci-0000:00:1f.2-scsi-4:0:0:0 -> ../../sr0
--------------------------------------------------------------------
root@ctrlpc1:/dev# tree |grep sr0
│   ├── 11:0 -> ../sr0
├── cdrom -> sr0
├── cdrw -> sr0
│   │   └── pci-0000:00:1f.2-scsi-4:0:0:0 -> ../../sr0
├── dvd -> sr0
├── dvdrw -> sr0
├── scd0 -> sr0
├── sr0
---------------------------------------------------------------------


  Thanks,
  Jeong Han


On 04/18/2013 12:22 AM, Mark Rivers wrote:
> Folks,
>
> I have a couple of questions about how to automatically set up USB serial devices on Linux.  I have a Newport motor controller which is a USB device, but is actually a "serial" device.  I can configure it fine on Linux by plugging it in and executing the following 2 commands as root:
>
> modprobe ftdi_sio vendor=0x104d product=0x3000
> chmod o+rw /dev/ttyUSB0

> The first command loads the ftdi_sio driver with the vendor and product codes for this device.  Those codes can be determined from the lsusb command:
>
> Colorado:motor/iocBoot/iocWithAsyn>/usr/sbin/lsusb
> Bus 002 Device 003: ID 104d:3000 Newport Corporation
>
> The second command sets the permissions on the device so any user can read and write it.
>
> After doing those commands my EPICS IOC can access the device, set the baud rate, data bits, stop bits, etc.  I now have a motor record driver to talk to it.
>
> My question is how to have those 2 commands executed automatically so I don't need to manually do it.  My first thought was to create a udev entry for the device.  I created the following file and put it in /etc/udev/rules.d
>
> Colorado:motor/iocBoot/iocWithAsyn>more ~/81-Agilis.rules
> SYSFS{idVendor}=="104d", ATTRS{idProduct}=="3000", MODE="0666"
>
> If this file is present after the Linux system is booted and after I have issued the "modprobe" command then it works correctly.  Each time I unplug the device /dev/ttyUSB0 disappears, and each time I plug it in it reappears with the correct permissions.  If the udev file is not present then when I plug it in the device is missing read/write permission for others.
>
> However, if that udev file is present when the system boots, before I issue the "modprobe" command then the "modprobe" command does not work in the sense that no /dev/ttyUSBn device appears.  I think this could be because the udev file is causing some other driver to load, and so it won't load the ftdi_sio driver.  Is there a way to specify which driver to load in the udev file?
>
> Does anyone know how to do this?
>
> I have a related question.  An EPICS user at NIH has 18 of these devices which he wants to use at the same time.  Is there a way to assign a specific device (based upon its serial number for example) to a  specific /dev/ttyUSBn port?  If not,  how does one figure out which motor is connected to which /dev/ttyUSBn port?
>
> Thanks,
> Mark

--
Jeong Han Lee, Dr.rer.nat.
---------------------------
Accelerator Division
Rare Isotope Science Project
Institute for Basic Science
70, Yuseong-daero 1689-gil, Yuseong-gu,
Daejeon 305-811, South Korea
---------------------------
cell : +82-10-7363-2083
tel  : +82-42-878-8733
fax  : +82-42-878-8799