[BRLTTY] Problem connecting the braille display Brailliant BI 40

[Didier Spaier]

On 12/11/2015 23:29, Mario Lang wrote:
> Shérab <Sebastien.Hinderer at ens-lyon.org> writes:
> 
>> Hello Didier,
>>
>> Thanks a lot for your response.
>>
>> Didier Spaier (2015/11/12 21:13 +0100):
>>> I am not sure that I understand your question.
>>>
>>> In brltty-5.2 this is done installing the file
>>> 40-usb-brltty.rules in /lib/udev, or do I miss something?
>>
>> I am on Deban andhave brltty 5.2~20141018-5+b2 installed,it seems this
>> is themost recent version of thepackage.
>>
>> I used this command:
>>
>> dpkg -L brltty | grep udev
>>
>> And the only result I got was:
>>
>> /usr/share/doc/brltty/examples/udev.rules.gz
>>
>> And I confirm that under/lib/udev/ nothing matches *brltty*
> 
> Yes, because udev-activation is not enabled on Debian by default.
> You are free to use the example file provided to configure your system
> to use it.
> I'd be interested in hearing how it works for you, after you give it
> some time for testing.
> 
>> So I think that indeed if the file you mention would be there everything
>> would work fine but it's not! :)
> 
> I am not quite sure that *everything* would work just fine.
> The problem here is that udev rules can basically just be used
> to do auto-activation if you use USB.  However, not all
> configurations do exclusively use USB.  My laptop, for instance,
> has BRLTTY configured to find my display *either* via USB or Bluetooth.
> This has prooven to be very helpful once my bluetooth stack broke.
> 
> Additionally, some people are still using serial braille displays.
> These can also not be handled by udev (AFAIK).
> 
> If we enable udev activation by default, we need to teach the users
> additionally about the fact that in some cases, they will have to enable
> the daemon, and in some other cases they dont.
> 
> I am personally not ready to open that can of worms yet.
> Especially, because I don't really see what we would be gaining.
> Most of us have BRLTTY around on their systems most of the time anyway.
> And if resource consumption is a problem, for instance, on an embedded
> system, you can still manually drop these udev rules into your system
> configuration and use them.  However, maybe I am missing an obvious
> point.
> Why is it particularily pressing to give up control about launching
> brltty?  Just another link in a chian of things that should never break.
> 
Well, I am not acquainted with Debian and am a Slackware user so all the
systemd thing escapes me, but what I do is as simple a shipping the
udev rules and:
_ If a Braille display was used at during installation (it was if brltty
  was set in the command line), then make the startup script
  /etc/rc.d/rc.brltty executable
_ If not, just let it not executable (changing that is just a magtter of
  "chmod 755/etc/rc.d.rc.brltty")

At boot, /etc/rc.d/rc.S starts the daemon if and only if the startup script
is executable.

I imagine that something similar could be done with the systemd services?

Furthermore I fail to see an inconvenience to start the daemon even if no
Braille display is in use, or if a Bluetooth connected device is used:
the rules wont be triggered then, that's all.

But maybe _I_ miss something obvious?
Cheers,
Didier