bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Martdur — Mon, 11 Sep 2023 08:45:50 GMT

Hi Hung Bui,

Thanks a lot for your help !

I'll check later where in my subrscibe procedure I enable CCCD and can get the BT_ATT_ERR_AUTHENTICATION .

Have a great week.

Best regards.

Martin

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Hung Bui — Mon, 11 Sep 2023 07:42:18 GMT

Hi Mart,

Usually service discovery should not fail. Usually you don't need to be paired to do service discovery.
After service discovery successfully, you should try to read/write the characteristic values or most commonly try to enable CCCD. If you can't read or write a characteristic(s) and get BT_ATT_ERR_AUTHENTICATION you should start pairing.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Martdur — Fri, 08 Sep 2023 14:17:12 GMT

So If I understand it right:

I launch the discovery procedure
On discovery_fail_cb
- If the error is related to authentification -> Launch pairing procedure.
On security changed re-launch the discovery procedure.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Hung Bui — Fri, 08 Sep 2023 13:48:14 GMT

Hi Mart,
It's hard to say.

But what you can do is to not requesting pairing when you connected.

You can wait until you read/write a characteristic and receive either BT_ATT_ERR_AUTHENTICATION or BT_ATT_ERR_INSUFFICIENT_ENCRYPTION then you can start pairing. That how it's normally done on the phone.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Martdur — Fri, 08 Sep 2023 13:21:14 GMT

Excatly Hung !

It works when I don't pair with the sensor.

The last question :

How I will I'm able to know that a sensor will not support pairing like this sensor do?

Because I wan't to be compliant with all kind of device.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Hung Bui — Fri, 08 Sep 2023 13:09:52 GMT

The only major difference I can see is that in the new trace you sent there were no pairing/bonding. When with the nrf53 central, it was pairing with the device.
Usually it's the opposite that you need to pair to be able to use the device, but I don't know about this device. Maybe you can try to not pair with the peripheral to see if it works.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Martdur — Fri, 08 Sep 2023 12:50:33 GMT

Yes it's a third party sensor made by powertap.

It tested it with the nrf connect app on phone and I could subscribe to the characteristic.

I don't know why it work with the phone, I'm investigating.

Here the response and the traces file :

devzone.nordicsemi.com/.../2100.BleAtTimeout.pcapng

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Hung Bui — Fri, 08 Sep 2023 12:20:16 GMT

Hi Martin,
What I can see is that the central tried to do a write request to the peripheral but it never got a write response, hence a ATT Timeout. The connection is terminated after 30 seconds because of that:

So it's correct that the issue is when the central trying to enable notification on the cycling power measurement service.
We need to look into the peripheral code to see why it doesn't response ?
Is it a 3rd party sensor ? If it is you may want to capture how it react when you connect with a phone and their native app to control the sensor.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Martdur — Fri, 08 Sep 2023 12:05:05 GMT

Hello Hung,

Sorry for the late response I was busy with another topic.

Thanks for the help, I managed to get proper traces.

The central is scanning and connecting to the concerned device then it performs a discovering and then subscribes to the cpwr measurement characteristic.

Then we have this timeout error.

Here the file:

devzone.nordicsemi.com/.../BleAtTimeout.pcapng

Thanks in advance.

Martin.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Hung Bui — Tue, 05 Sep 2023 11:09:07 GMT

Hi Mart,

You would need to select the advertiser in the drop down list so that the sniffer would follow the connection instead of just scanning for advertising packets.
We have a tutorial here for nRF Sniffer. It's to be used with nRF Connect examples, but the principle is the same.
https://academy.nordicsemi.com/courses/bluetooth-low-energy-fundamentals/lessons/lesson-6-bluetooth-le-sniffer/topic/blefund-lesson-6-exercise-2/

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Martdur — Mon, 04 Sep 2023 10:37:29 GMT

Hi Hung,

My bad I missed something in the tutorial.

I managed to make the nrf sniffer working but I don't understand the trace I had, it's seems that the connexion is bugged after a while.

In the same time I've realized that the central is detecting this sensor with delay so I increased the scan window, and this seems to solve this issue but I still I have the At timeout error.

The concerned peripheral address : 6c b8 f0 94 78 d2

Here the sniffer trace:

/cfs-file/__key/communityserver-discussions-components-files/4/BlePaquert_5F00_FailedToDiscover.pcapng

/cfs-file/__key/communityserver-discussions-components-files/4/BlePaquert_5F00_FailedToDiscover2.pcapng

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Martdur — Fri, 01 Sep 2023 15:13:45 GMT

Thanks but I get this, I think I launch the command from the wrong directory, am I right ?

C:\Users\dev>cd C:\Program Files\Wireshark\extcap

C:\Program Files\Wireshark\extcap>py -3 -m pip install -r requirements.txt.
Requirement already satisfied: colorama==0.4.6 in c:\users\dev\appdata\local\programs\python\python311\lib\site-packages (from -r requirements.txt. (line 1)) (0.4.6)
Requirement already satisfied: docopt==0.6.2 in c:\users\dev\appdata\local\programs\python\python311\lib\site-packages (from -r requirements.txt. (line 2)) (0.6.2)
Requirement already satisfied: packaging==23.1 in c:\users\dev\appdata\local\programs\python\python311\lib\site-packages (from -r requirements.txt. (line 3)) (23.1)
Requirement already satisfied: pykwalify==1.7.0 in c:\users\dev\appdata\local\programs\python\python311\lib\site-packages (from -r requirements.txt. (line 4)) (1.7.0)
Requirement already satisfied: python-dateutil==2.8.2 in c:\users\dev\appdata\local\programs\python\python311\lib\site-packages (from -r requirements.txt. (line 5)) (2.8.2)
Requirement already satisfied: PyYAML==6.0 in c:\users\dev\appdata\local\programs\python\python311\lib\site-packages (from -r requirements.txt. (line 6)) (6.0)
Requirement already satisfied: six==1.16.0 in c:\users\dev\appdata\local\programs\python\python311\lib\site-packages (from -r requirements.txt. (line 7)) (1.16.0)
Requirement already satisfied: west==1.0.0 in c:\users\dev\appdata\local\programs\python\python311\lib\site-packages (from -r requirements.txt. (line 8)) (1.0.0)
Requirement already satisfied: setuptools in c:\users\dev\appdata\local\programs\python\python311\lib\site-packages (from west==1.0.0->-r requirements.txt. (line 8)) (65.5.0)

C:\Program Files\Wireshark\extcap>

Edit : And the folder is still empty.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Hung Bui — Fri, 01 Sep 2023 14:01:18 GMT

Hi Mart,

Python folder should be added to the System Environment Variables in Windows. In that you need to add the python folder in to the Path so that it can be called in any folder:

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Martdur — Fri, 01 Sep 2023 13:54:03 GMT

I didn't managed to get further than the chapter 1.2 of Installing the nrf sniffer capture tools.

Can you provide me more information on which folder I need to lauchn the : pip c"py -3 -m pip install -r requirements.txt" command please.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Martdur — Fri, 01 Sep 2023 13:16:34 GMT

Hi Hung,

Thanks for your response.

I have no control over the peripheral, maybe you have a sample code that simulate a cycling power sensor.

No there no assert on my side just this error.

I realized that I have thoses two line in the log that I don't with other sensor :

[00:00:17.566,650] <inf> BLE: le_param_req: LE conn param req: D2:78:94:F0:B8:6C (random) int (0x0020, 0x00a0) lat 4 to 500
[00:00:24.565,734] <inf> BLE: le_param_updated: LE conn param updated: D2:78:94:F0:B8:6C (random) int 0x00a0 lat 4 to 500

I'll try do use the sniffer and come back to you.

RE: bt_att: att_timeout: ATT Timeout error after subscribing succesfully.

Hung Bui — Fri, 01 Sep 2023 11:13:09 GMT

Hi Mart,

I would suggest to capture a sniffer trace to see what happens over the air. I'm not so sure on which exact ATT request that got timed out. There is a tutorial on how to use the sniffer trace in this course: https://academy.nordicsemi.com/courses/bluetooth-low-energy-fundamentals/lessons/lesson-6-bluetooth-le-sniffer/

Do you have control over the peripheral's side ? Was there any assert ?