Re: Problems reading characteristics with Bluez 5.52

From: Peter Belau <pbelau1@gmail.com>
To: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc: "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>
Subject: Re: Problems reading characteristics with Bluez 5.52
Date: Thu, 2 Jan 2020 19:57:58 -0600	[thread overview]
Message-ID: <CAAERL8SK8rHhhGFN95+gWZF-2K4vozRcmZkA5aU9Fwx3a58+7w@mail.gmail.com> (raw)
In-Reply-To: <CABBYNZLe=ZmiPXg8mrU2BxY9H0hv_WvkvigyJBAs_wnq5ct_Cg@mail.gmail.com>

Thank you very much for the response;  I did not realize that
'indicate' was exclusive to doing an attribute read. However, "notify
on" doesn't seem to help. The device disconnects after a read and now
I can no longer connect to it at all:

QardioARM:/service0400/char0410]# notify on
Notify started
[CHG] Device 5C:D6:1F:0E:0A:7D ServicesResolved: no
[CHG] Device 5C:D6:1F:0E:0A:7D Connected: no

[bluetooth]#  connect 5C:D6:1F:0E:0A:7D

Attempting to connect to 5C:D6:1F:0E:0A:7D
Failed to connect: org.bluez.Error.Failed

On the bluetoothd side I'm seeing:

bluetoothd[20426]: src/agent.c:agent_disconnect() Agent :1.626 disconnected
bluetoothd[20426]: src/agent.c:remove_default_agent() Default agent cleared
bluetoothd[20426]: src/adapter.c:set_mode() sending set mode command for index 0
bluetoothd[20426]: src/agent.c:agent_destroy() agent :1.626
bluetoothd[20426]: src/agent.c:agent_unref() 0x55e718787df0: ref=0
bluetoothd[20426]: src/adapter.c:new_settings_callback() Settings: 0x00000a01
bluetoothd[20426]: src/adapter.c:settings_changed() Changed settings: 0x00000010
bluetoothd[20426]: src/adapter.c:settings_changed() Pending settings: 0x00000000
bluetoothd[20426]: src/agent.c:add_default_agent() Default agent set
to :1.627 /org/bluez/agent
bluetoothd[20426]: src/adapter.c:set_mode() sending set mode command for index 0
bluetoothd[20426]: src/agent.c:agent_ref() 0x55e7187b7a00: ref=1
bluetoothd[20426]: src/agent.c:register_agent() agent :1.627
bluetoothd[20426]: src/adapter.c:new_settings_callback() Settings: 0x00000a11
bluetoothd[20426]: src/adapter.c:settings_changed() Changed settings: 0x00000010
bluetoothd[20426]: src/adapter.c:settings_changed() Pending settings: 0x00000000
bluetoothd[20426]: src/device.c:att_connect_cb() connect error:
Connection refused (111)

I should note that I've tried a number of BTLE blood pressure devices
with a variety of BT controllers and Bluez cannot seem to maintain
reliable connections with any of the configurations I've tried. Any
help would be much appreciated.

On Thu, Jan 2, 2020 at 7:30 PM Luiz Augusto von Dentz
<luiz.dentz@gmail.com> wrote:
>
> Hi Peter,
>
> On Thu, Jan 2, 2020 at 5:22 PM Peter Belau <pbelau1@gmail.com> wrote:
> >
> > I'm trying to get a Qardio ARM BP monitor working with Linux/Bluez but
> > cannot seem to read any device characteristics with Bluez. My
> > interaction through bluetoothctl looks like this:
> >
> > # menu gatt
> > # attribute-info  00002a35-0000-1000-8000-00805f9b34fb
> > Characteristic - Blood Pressure Measurement
> >     UUID: 00002a35-0000-1000-8000-00805f9b34fb
> >     Service: /org/bluez/hci0/dev_B0_49_5F_02_B5_61/service0400
> >     Value:
> >   16 7f 00 49 00 5b 00 00 00 00 00 00 00 00 35 00  ...I.[........5.
> >   00 00                                            ..
> >     Notifying: no
> >     Flags: indicate
> > # select-attribute 00002a35-0000-1000-8000-00805f9b34fb
> > # read
> > # Attempting to read /org/bluez/hci0/dev_B0_49_5F_02_B5_61/service0400/char0410
> > Failed to read: org.bluez.Error.Failed
> >
> > I have bluetoothd running with debug flags but nothing appears in the
> > debug logs. What am I doing wrong?
>
> Look at the flags, it only has indicate so it doesn't support reading directly.
>
> --
> Luiz Augusto von Dentz