[COLUG] USB to serial converter, udev rule making, one problem solved

[charles morrison]

To All:
Review of problem.
The initial request for ideas came from my attempt to install a qbasic 
program under dosemu in which I discovered that the dosemu would not 
recognize my serial port which is a USB to serial converter. There are 
actually two problems: the first is that even though our qbasic program 
runs under dosemu, the serial port did not work, and the second was that 
the symlink created using udev rules did not work. I have solved the 
mystery of the second problem.

The reason for using udev was to create a known point to communicate to 
DOS devices using a USB to serial converter. Typically, DOS programs use 
COM1, COM2, etc as devices. They must always be at the same device node, 
or else when plugging and unplugging devices, the DOS program cannot 
search and adjust its node point, so a fixed node name is desired. I 
used udev to create this device name as /dev/COM1 for this program. Then 
the /etc/dosemu/dosemu.conf file can be adjusted to always look at 
/dev/COM1 as COM1 for all DOS programs. Similarly, a symlink can then be 
used under WINE in the dosdevices directory.

My udev rules worked and created a symlink to a COM1, to which I could 
never send data, even though it worked for the original device node and 
under a dosemu command prompt. The reason was in the manner in which 
udev creates symlinks (which I do not fully understand).

My current and working rule is for a Belkin USB to serial converter:

/SUBSYSTEMS=="usb-serial", DRIVERS=="mct_u232", SYMLINK+="COM1", 
GROUP="dialout", MODE="777"/

This recognizes the USB to serial converter when it is plugged in and 
then adds a symlink to it as /dev/COM1.
The problem arose due to matching udev parameters, but not at the 
correct level in the hierarchy.

Explanation:

 Using the /udevinfo -a -p $(udevinfo -q path -n /dev/ttyUSB0)/ command 
yields:

looking at device '/class/tty/ttyUSB0':
    KERNEL=="ttyUSB0"
    SUBSYSTEM=="tty"
    DRIVER==""
    ATTR{dev}=="188:0"

  looking at parent device 
'/devices/pci0000:00/0000:00:13.0/usb1/1-1/1-1:1.0/ttyUSB0':
    KERNELS=="ttyUSB0"
    /SUBSYSTEMS=="usb-serial"/
    /DRIVERS=="mct_u232"/

  looking at parent device 
'/devices/pci0000:00/0000:00:13.0/usb1/1-1/1-1:1.0':
    KERNELS=="1-1:1.0"
    SUBSYSTEMS=="usb"
    DRIVERS=="mct_u232"
    ATTRS{modalias}=="usb:v050Dp0109d0102dc00dsc00dp00icFFiscFFipFF"
    ATTRS{bInterfaceProtocol}=="ff"
    ATTRS{bInterfaceSubClass}=="ff"
    ATTRS{bInterfaceClass}=="ff"
    ATTRS{bNumEndpoints}=="03"
    ATTRS{bAlternateSetting}==" 0"
    ATTRS{bInterfaceNumber}=="00"

  looking at parent device '/devices/pci0000:00/0000:00:13.0/usb1/1-1':
    KERNELS=="1-1"
    *SUBSYSTEMS=="usb"*
    DRIVERS=="usb"
    ATTRS{serial}=="927135"
    *ATTRS{product}=="Belkin Components"*
    ATTRS{manufacturer}=="Belkin USB PDA Adapter"
    ATTRS{quirks}=="0x0"
    ATTRS{maxchild}=="0"
    ATTRS{version}==" 1.10"
    ATTRS{devnum}=="4"
    ATTRS{busnum}=="1"
    ATTRS{speed}=="12"
    ATTRS{bMaxPacketSize0}=="16"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bDeviceClass}=="00"
    ATTRS{bcdDevice}=="0102"
    ATTRS{idProduct}=="0109"
.
.
.
.


When I used the wrong parameters *
   SUBSYSTEMS=="usb"/ /and*
    *ATTRS{product}=="Belkin Components"
*I got a symlink which did not work and was of the form: crwxrwxrwx 1 
root dialout 254, 11 2007-12-18 11:16 ./usbdev1.4_ep02, and also did not 
work, since major device 254 is an experimental device node.

When I moved up into the udev description and used
    /SUBSYSTEMS=="usb-serial"/
    /DRIVERS=="mct_u232"
/the symlink became
lrwxrwxrwx 1 root   root           7 2007-12-18 11:43 COM1 -> ttyUSB0

and it now works just as well as if I were using /dev/ttyUSB0.

This problem is solved, but I still have not gotten my qbasic program to 
use the serial port.

Charlie Morrison

//

-- 
Charlie Morrison
American LED-gible, Inc
1776 Lone Eagle Street
Columbus, OH  43228  USA
614-851-1100
FAX  614-851-1121
We use ISO 26300 document standards available through Open Office at http://www.openoffice.org