[BRLTTY] Repeated Bluetooth pairing request on Android

[Dave Mielke]

[quoted lines by Robert Pösel on 2018/03/06 at 10:15 +0100]

>while reading Android documentation I come to this recommendation:
>
>"Note: You should always call cancelDiscovery() to ensure that the
>device isn't performing device discovery before you call connect().
>If discovery is in progress, then the connection attempt is
>significantly slowed, and it's more likely to fail." (https://developer.android.com/guide/topics/connectivity/bluetooth.html)

Since brltty doesn't do discovery (it only connects to already-paired devices), 
and since discovery is a rare action, arbitrarily cancelling discovery is a 
surprise that I don't believe we should be inflicting on people. :-) I think 
it's rather unlikely that someone would be trying to connect to a braille 
device and doing Bluetooth discovery at the same time.

>I don't see any call to BluetoothAdapter.cancelDiscovery() so it
>might be good idea to add it? On the other hand, since you are
>calling the connect() method repeatedly every few seconds, it would
>mean that bluetooth discovery will never have a chance to finish (as
>cancelling it has global effect for whole system). So unless this
>automatic repeated connection will be rewritten somehow, current way
>without cancelDiscovery() is perhaps okay?

Yes, I think cancelling discovery wouldn't be a good thing to do.

>what about power consumption and battery life regarding these
>repeated connection attempts? Do you know if it has any impact or is
>it "safe" to use this way?

I agree with you that retrying every few seconds isn't nice, but I haven't yet 
come up with a better way to do it. There's no obvious way for brltty to know 
that a new Bluetooth device has been turned on, come within range, etc.

Note that brltty doesn't try while the Android device is locked. This itself 
goes a long way to not needlessly draining the battery, although the main 
reason it's done that way is to allow a person to switch between devices (lock 
one, awaken another). So, the only time when brltty is retrying is when it 
isn't yet connected to a braille device while the Android device is awake.

-- 
I believe the Bible to be the very Word of God: http://Mielke.cc/bible/
Dave Mielke           | 2213 Fox Crescent | WebHome: http://Mielke.cc/
EMail: Dave at Mielke.cc | Ottawa, Ontario   | Twitter: @Dave_Mielke
Phone: 1-613-726-0014 | Canada  K2A 1H7   |