[BRLTTY] Baum driver not stable

[André-Abush Clause]

Hello,

Since several weeks, I search to run BRLTTY with driver Baum. 
Unfortunately, it seems that it doesn't work. Indeed, BRLTTY crashes 
constantly when I using keyboard.

A long series of beeps are emit, the connection with the VarioUltra is 
lost, and I have to kill and restart the BRLTTY if I want to find the 
braille again.

Sometimes, this happens just A Few Seconds After Starting BRLTTY without 
any action on my part.

I don't have this problem with my old braille display.

Below any excerpts from a BRLTTY log:

```
2016-06-23 at 23:12:53.389 [brltty] BRLTTY 5.3.1 rev 
BRLTTY-5.3.1-153-ge740c2ca [http://brltty.com/]
2016-06-23 at 23:12:53.389 [brltty] lock descriptor allocated: 
queue-discarded-elements
2016-06-23 at 23:12:53.390 [brltty] Log Level: debug
[....]
2016-06-23 at 23:12:55.592 [tune-thread] tone: MSecs:100 Freq:440
2016-06-23 at 23:12:57.593 [tune-thread] beeper disabled
2016-06-23 at 23:13:00.564 [brltty] USB bulk transfer error 110: Connection 
timed out.
2016-06-23 at 23:13:00.564 [brltty] popped command handler: message
2016-06-23 at 23:13:00.564 [brltty] popped command environment: message
2016-06-23 at 23:13:00.564 [brltty] report listener registered: 0: 
brlapi_handleReports
2016-06-23 at 23:13:01.564 [brltty] USB bulk transfer error 110: Connection 
timed out.
2016-06-23 at 23:13:01.564 [brltty] activity action request: 
braille-driver: stop
2016-06-23 at 23:13:01.564 [brltty] activity state change: braille-driver: 
9[stopping]
2016-06-23 at 23:13:01.564 [brltty] report listener unregistered: 0: 
brlapi_handleReports
2016-06-23 at 23:13:01.587 [brltty] activity state change: braille-driver: 
0[stopped]
2016-06-23 at 23:13:01.587 [brltty] reinitializing braille driver
2016-06-23 at 23:13:01.587 [brltty] activity action request: 
braille-driver: start
2016-06-23 at 23:13:01.587 [brltty] activity state change: braille-driver: 
4[preparing]
[...]
2016-06-23 at 23:13:01.954 [brltty] cannot open file: /etc/brltty-bm.prefs: 
No such file or directory
[...]
2016-06-23 at 23:12:55.592 [tune-thread] tone: MSecs:100 Freq:440
2016-06-23 at 23:12:57.593 [tune-thread] beeper disabled
2016-06-23 at 23:13:00.564 [brltty] USB bulk transfer error 110: Connection 
timed out.
[...]
2016-06-23 at 23:13:01.587 [brltty] reinitializing braille driver
[...]
2016-06-23 at 23:13:14.052 [brltty] USB control transfer error 110: 
Connection timed out.
2016-06-23 at 23:13:14.052 [brltty] USB configuration descriptor not 
readable: 0
2016-06-23 at 23:13:14.052 [brltty] USB configuration descriptor not found: 1
2016-06-23 at 23:13:14.052 [brltty] braille driver initialization failed: 
bm -> usb:
2016-06-23 at 23:13:14.052 [brltty] braille driver not found
2016-06-23 at 23:13:14.052 [brltty] activity action failed: braille-driver: 
start
2016-06-23 at 23:13:14.052 [brltty] activity state change: braille-driver: 
2[scheduled]
2016-06-23 at 23:13:14.052 [brltty] activity state change: braille-driver: 
6[starting]
[...]
2016-06-23 at 23:13:15.055 [brltty] USB language code string read error
[...]
2016-06-23 at 23:13:24.112 [brltty] USB: interface descriptor not found: 0.0
[...]
2016-06-23 at 23:13:33.382 [brltty] USB configuration set error 32: Broken 
pipe.
[...]
```

For a more complete log, please see <http://dl.andreabc.net/brltty.log>.

Do you have an idea of the problem please? How to resolve it?

Thanks in advance for your responses,

André