Re: Bluetooth disconnect event / Link layer monitoring

[Guy Morand <g.morand@scewo.ch>]

Thanks everyone for your quick answers!

I tried this already but unfortunately, it seems that the gamepad
doesn't allow that:
$ hcitool lst ec:83:50:de:02:3c 1
HCI write_link_supervision_timeout request failed: Input/output error

< HCI Command: Write Link Supervision Timeout (0x03|0x0037) plen 4
    handle 70 timeout 1
> HCI Event: Command Complete (0x0e) plen 6
    Write Link Supervision Timeout (0x03|0x0037) ncmd 1
    status 0x0c handle 70
    Error: Command Disallowed

Yes, if it was me, I would never use bluetooth!

I guess the only place where I can do something is in the kernel space.
I would like to send the error to the user when this happens:
Bluetooth: hci0 link tx timeout

Do you think that would be possible and make sense?

Best regards,

Guy

On Tue, Nov 19, 2019 at 6:06 AM Marcel Holtmann <marcel@holtmann.org> wrote:
>
> Hi Luiz,
>
> >> 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.
>
> we can add an option to L2CAP sockets to adjust the link supervision timeout.
>
> Anyway, these days, I would _not_ use Bluetooth BR/EDR for controlling anything. I would find a Gamepad that utilizes Bluetooth LE and focus on that.
>
> Regards
>
> Marcel
>


-- 

Guy Morand

Software Engineer

–

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