[BRLTTY] Get rid of braille display keys occasionally not working

[Mario Lang]

Lars Bjørndal <lars at lamasti.net> writes:

> On Fri, Aug 11, 2017 at 11:17:38AM +0200, Lars Bjørndal wrote:
>> Hi, Mario!
>> 
>> Another note:
>> 
>> On the system where I have connection problems, I sometimes experience
>> that a key press on the braille display doesn't do anything. The
>> display, however, moves when the cursor is moved.
>> 
>> Some lines from the log says:
>> 
>> aug. 11 05:06:56 kul3 brltty[1032]: input byte missing at offset 0
>> aug. 11 05:06:56 kul3 brltty[1032]: Partial Packet: 79
>> aug. 11 05:07:21 kul3 brltty[1032]: autoreleasing key: ? (Grp:0 Num:2)
>> aug. 11 05:07:21 kul3 brltty[1032]: autoreleasing key: B3 (Grp:0 Num:11)
>> aug. 11 05:07:21 kul3 brltty[1032]: autoreleasing key: ? (Grp:0 Num:22)
>> aug. 11 05:07:21 kul3 brltty[1032]: autoreleasing key: ? (Grp:0 Num:84)
>> aug. 11 05:07:21 kul3 brltty[1032]: autoreleasing key: ? (Grp:0 Num:85)
>> aug. 11 05:08:43 kul3 brltty[1032]: input byte missing at offset 0
>> aug. 11 05:08:43 kul3 brltty[1032]: Partial Packet: 79 54 02
>> aug. 11 05:09:03 kul3 brltty[1032]: autoreleasing key: ? (Grp:0 Num:22)
>

[...]

> The BRLTTY release is 5.5. I use a Handy Tech Active Braille.
>
> Please tell me if I can do anything more to investigate the keys not
> working problem. In the mean time, I have to restart BRLTTY from time
> to time, to get the keys working again.

I know that a slightly unstable Bluetooth connection can lead to lost
key presses (or releases).  This was the reason why Dave implemented
auto key release in BRLTTY 5.5.  What that does is to automatically
release keys that have been pressed for a seemingly long time.  This,
at least for me, made the issue of having to restart BRLTTY due to a
lost key release go away.  When this happens, I just wait a few seconds
until BRLTTY automatically releases the stuck key, and I can continue to
work as usual.  However, I should probably also explain that I have
changed my Bluetooth host controller chip in the meanwhile, from an USB
dongle that used to be connected to my Pi Zero, to the internal
Bluetooth chip that comes with the new Pi Zero W.  That change resulted
in a more stable bluetooth connection.  I am using an Active Star
though, so we can't really compare our results.

While I can not really be sure, I am guessing that most Bluetooth
problems around Raspberry setups actually come from unstable hardware on
the Raspberry side.  Even the USB port of a "full-blown" Raspberry Pi 3
feels a bit weak to a Handy Tech user.  When I connect my Modular
Evolution directly to the USB port of a Raspberry Pi 3, things basically
work fine, but the Modular Evolution resets itself (with an audible
beep) every 10 or 20 minutes.  To me, this indicates some problems with
power, since I have never seen that behaviour with a normal PC USB port.

To answer your question: All I can suggest is to try and switch
to a differen bluetooth host controller, and, check in the BRLTTY
preferences how long auto key release is set for you.  Experiment
with that setting, maybe it helps.  This only makes sense though, if
your Bluetooth connection is at least stable enough to basically work,
but only sometimes loose a key event.  If it is unstable to a point
where too much data gets lost, I am afraid there is not much really
we can do on the side of BRLTTY to imrove that.

-- 
CYa,
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