Re: Bluetooth disconnect event / Link layer monitoring

[Luiz Augusto von Dentz <luiz.dentz@gmail.com>]

Hi Guy,

On Mon, Nov 18, 2019 at 7:19 PM Guy Morand <g.morand@scewo.ch> wrote:
>
> Hello bluetooth developers,
>
> We are developing a wheelchair that we can controle with a bluetooth
> gamepad, the XBOX 360 controller to be more precise. It basically works
> fine but when I remove the battery, I get the disconnect event in the
> user space around 10 seconds later. That is not acceptable since the
> wheelchair will keep rolling to potentially dangerous places!
>
> I tried to implement a ping mechanism on the bluetooth layer, inspired
> from bluez sources somewhere:
>   int _socket_fd = socket(PF_BLUETOOTH, SOCK_RAW, BTPROTO_L2CAP);
>   // bind on AF_BLUETOOTH
>   // connect with AF_BLUETOOTH
>
>   send_cmd->ident = PING_IDENT;
>   send_cmd->len = htobs(PING_DATA_SIZE);
>   send_cmd->code = L2CAP_ECHO_REQ;
>   if (send(_socket_fd, send_buffer, PING_PACKET_SIZE, 0) <= 0) {
>     // ...
>   }
>
> It basically works fine except when the signal gets bad. This will get
> printed by the kernel:
> [  859.629431] Bluetooth: hci0 link tx timeout
> [  859.635482] Bluetooth: hci0 killing stalled connection 9c:aa:1b:6b:51:c9
>
> In that case, I don't get event from the /dev/jsX device but the gamepad
> seems to still answer to pings??!!
>
> Since I haven't found any acceptable workaround and always find the same
> pages again and again, I'm asking here:
> * Is it possible to achieve what I want?
> * Does it make sense that the ping work but the HID layer seems dead?
> * Any recommendation, pointers?

Id look into adjusting the link supervision timeout instead of
creating a raw socket, you can use hcitool to do that, neither is
really great since it require root but at least the supervision
timeout is something a lot more reliable for this.

-- 
Luiz Augusto von Dentz