[Owfs-developers] Fwd: Re: Problem starting owserver on a LinkUSB with option ftdi addressing without sudo

[Martin P. (GMX) <Mar...@gm...>]

sorry, forgot to hit 'reply all'...


-------- Forwarded Message --------
Subject: 	Re: [Owfs-developers] Problem starting owserver on a LinkUSB 
with option ftdi addressing without sudo
Date: 	Thu, 10 Aug 2017 19:01:07 +0200
From: 	Martin Patzak (GMX) <Mar...@gm...>
To: 	Eloy Paris <pe...@ch...>





On 10.08.2017 18:06, Eloy Paris wrote:
> Hi Martin,
>
> On Thu, Aug 10, 2017 at 03:22:19PM +0200, Martin Patzak (GMX) wrote:
>
> [...]
>
>
> A small enhancement that you can add and use is to have udevd create
> a predictable symlink for the device. This way if you plug in more
> USB devices, or plug things in a different order so they get assigned
> the same /dev/ node that your LinkUSB currently has, your owserver or
> whatever programs use your LinkUSB will still be able to find it.
>
> As an example, here's what I have on my
> /etc/udev/rules.d/50-local-usb-serial.rules file:
>
> ----------------------------------------------------------------------
> #
> # Fromhttp://marc.merlins.org/perso/linuxha/2010-06.html#Dealing-with-many-USB-to-Serial-Port-Converters-on-linux-and-device-naming
> #
> # After making a change 'udevadm trigger' will update symlinks.
> #
>
> #http://www.reactivated.net/writing_udev_rules.html#udevinfo
> # was udevinfo -a -p /class/tty/ttyUSB0
> # now udevadm info --attribute-walk -p /class/tty/ttyUSB0
> # (used to determine product ID, serial number, etc. to be used
> # in the declarations below)
>
> SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A5008b6u", SYMLINK+="plm"
> SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A400bXjP", SYMLINK+="1wire-master0"
> SUBSYSTEMS=="usb", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A800eIPR", SYMLINK+="1wire-master1"
> SUBSYSTEMS=="usb", ATTRS{product}=="FT231X USB UART", ATTRS{serial}=="DC00HJ03", SYMLINK+="moteino-usb"
> ----------------------------------------------------------------------
>
> These rules will create the symlinks /dev/plm, /dev/1wire-master0,
> /dev/1wire-master1, and /dev/moteino-usb for the FTDI serial-to-USB
> chips with those serial numbers. Applications (like owserver) then
> use the symlinks instead of the actual /dev/bus/usb/<n>/<m> path. For
> example, my /etc/owfs.conf contains this:
>
> server: device = /dev/1wire-master0
>
> Cheers,
>
> Eloy Paris.-
Hello Eloy,

thanks for your suggestion. I had a rule just like yours, but it was 
linked to the usb-serial device /dev/ttyUSB<n> and not /dev/bus/usb/<n>/<m>.
Can you please check, where your symlink actually points to?

But regardless, I recently learned, that in order to get direct ftdi 
communication in owserver, on has to address the device in a special 
way: ftdi:..., in my case, a LinkUSB, it looks like:

/owserver --link=ftdi:s:0x0403:0x6001:A800bXHr/

so i cannot use a symlink as address. But this way of addressing is also 
unique, because the serial number is also given, when using the option 
's:' (for serial number)

If you address the serial usb device, you only get native serial 
communication, like so

/owserver --link=/dev/ttyUSB<n>

/this is what I did in the beginning, and here you could use your 
symlink, but you won't get the speed advantage of direct communication, 
as Johan explained to me.

My problem then was, that I could only start owserver in direct 
communication mode, when I used 'sudo'. I did not know which node I have 
change the permission on in order to get owserver started. Matthias 
pointed out, that I have to talk to the raw usb device, which I then 
found resides in /dev/bus/usb/<n>/<m>, which is created by udev. Well 
there is a corresponding raw device created by SYSFS in 
/sys/platform/bla/bla/bla/deep/down/there, which also Matthias pointed 
out, but you don't have to bother with that.

Cheers,

Martin