BLE Device disconnection when calling via Handsfree profile on iOS with reason 722

Question

We develop our own BLE device and connect to iPhone. We discover an issue that it will disconnect after 2~3 minutes when making calls via Handsfree profile. (ex: Using car audio system, infotainment HUD or so). Please refer to the raw log below.

Does anyone know what status 722 stands for?
How do we resolve this?
Thanks.

Code Block default 2021-02-09 17:04:57.813774 +0800    bluetoothd  Server.LE.Connection    LE ConnManager disconnection complete reason 722 address=<private> localRole=Master
default 2021-02-09 17:04:57.816296 +0800    bluetoothd  Stack.GATT   _GATT_LE_DisconnectedCB on handle 0x000000014C804720 with reason  STATUS 722
default 2021-02-09 17:04:57.816977 +0800    bluetoothd  Server.LE   Device "E2278A91-B7B6-2122-696C-BE887487C8D7" set last connected time to 1612890297
default 2021-02-09 17:04:57.820707 +0800    bluetoothd  Stack.CL     Removing peer ID 0 for handle 0x000000014C804720
default 2021-02-09 17:04:57.820869 +0800    bluetoothd  Stack.HCI    Releasing LE connection 0x0041
default 2021-02-09 17:04:57.822551 +0800    bluetoothd  Server.LE.Connection    Device "E2278A91-B7B6-2122-696C-BE887487C8D7" does not require low latency
default 2021-02-09 17:04:57.822580 +0800    bluetoothd  Server.LE.Connection    Found link-ready device calling disconnection notification
default 2021-02-09 17:04:57.822582 +0800    bluetoothd  Server.LE.Connection    Disconnected from device "E2278A91-B7B6-2122-696C-BE887487C8D7" successfully (locally-initiated)
default 2021-02-09 17:04:57.822585 +0800    bluetoothd  Server.LE.Connection    linkReady:1 disconnectDevice:0 localRole:0 reason:722 result:0
default 2021-02-09 17:04:57.824928 +0800    bluetoothd  Server.LE.Security  Removing temporary security keys for device <private>

Core Bluetooth

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Posted by

brosso

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Answer 1

722 means the disconnection was locally-initiated (it also says so on the line just above).
"locally" in this context means iPhone side.

It could be caused by many things, from the iPhone not liking something the device is doing and terminating the connection, to something in your app which is closing the connection, perhaps a code path that is doing so, or perhaps you are somehow releasing or overwriting your CBManager or CBPeripheral objects by mistake.

The causes are many, but hard to make a guess from a log snippet here.

Posted by

Gualtier Malde

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Answer 2

Hi Gualtier,

Thanks for your reply.
After further inspect, we summarize logs from logarchive file.

BLE Disconnect logs

Here is the predicate we use to filter logs

Code Block --predicate '(subsystem == "com.apple.bluetooth") AND (category IN { "Stack.ATT", "Server.Audio", "Server.Handsfree", "Server.GATT", "Server.LE", "Server.LE.Connection", "Stack.HCI" })'

Our app reads values from our BLE beacon device every 60 seconds in the background once connected.
As you can see, at 2021-02-09 17:04:23.995037

Code Block bluetoothd: [com.apple.bluetooth:Server.GATT] Reading value for characteristic value handle 0x001b, char handle 0x001a on device "<private>"

The read command never got responded until 2021-02-09 17:04:53.971431

Code Block bluetoothd: [com.apple.bluetooth:Stack.ATT] Timeout waiting for ATT response, forcing a disconnect. (status=65535)

After that, a sequence of disconnecting logs popped out as we post previously.
Other read value logs would be almost immediately followed by statedump logs
We suspect this is the root cause of disconnection but we still need more hints to solve this.

It only happens along with active HFP.
Other than that our beacon is able to maintain stable connection with iPhone until battery dies out.

Any advice would be appreciated :)

Posted by

brosso

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BLE Device disconnection when calling via Handsfree profile on iOS with reason 722

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