nRF5340 LE disconnection Issue.

[AKV]

Hi,

We are using nRF5340 DK and the nRF Connect SDK Version 2.6.1.

We are experiencing an issue with disconnections. We use bt_conn_ref() when receiving the connected event and bt_conn_unref() when receiving the disconnection event.

However, sometimes after a disconnection, when we retry, we encounter the error: "bt_conn: bt_conn_exists_le: Found valid connection (0x20001a18) with address FF:F5:55:5A:D6:6A (random) in disconnected state".

Why does this issue occur even after the disconnection event has been processed?

If we call bt_conn_unref() twice during the disconnection event as shown in the below code (essentially incrementing once upon connection and decrementing twice upon disconnection), the issue does not occur.

void connected(struct bt_conn *conn, uint8_t conn_err){
	bt_conn_ref(conn);
}
void disconnected(struct bt_conn *conn, uint8_t reason){
 	bt_conn_unref(conn);
 	bt_conn_unref(conn);	
}

Could this behavior be due to an internal counter issue?

[Vidar Berg]

Hi,

I'm not aware of any known issues where the Bluetooth host fails to release its own reference. Are you developing a peripheral or central application?

Thanks,

Vidar

[AKV]

Hi, 

Thanks for the response.

We are developing a mesh network. Our requirement is the one device can connect to three other devices. Using one connection as a peripheral and up to two connections as a central for mesh connections.

[Vidar Berg]

Hi,

For the GAP central role, you should decrement the reference count in the connectected callback if the connection failed to be established: https://github.com/nrfconnect/sdk-nrf/blob/57e64dd9671a27f6d78172d5526cbedcbbebcc70/samples/bluetooth/central_and_peripheral_hr/src/main.c#L233. Clients need the connection object for performing service discovery. For the peripheral/server, it is often not necessary to increment the reference count.

[AKV]

Hi

Thanks for the response.

I followed the example implementation you suggested, but the issue persists. 

[dejans]

Hi,

Could you provide a complete log showing the error?

Best regards,
Dejan

[AKV]

Hi,

*** Booting nRF Connect SDK v3.5.99-ncs1-1 ***

[00:00:00.017,944] <inf> bt_hci_core: hci_vs_init: HW Platform: Nordic Semiconductor (0x0002)
[00:00:00.017,944] <inf> bt_hci_core: hci_vs_init: HW Variant: nRF53x (0x0003)
[00:00:00.017,974] <inf> bt_hci_core: hci_vs_init: Firmware: Standard Bluetooth controller (0x00) Version 54.58864 Build 1214809870
[00:00:00.019,805] <inf> bt_hci_core: bt_dev_show_info: Identity: FF:F5:55:5A:D6:6A (random)
[00:00:00.019,836] <inf> bt_hci_core: bt_dev_show_info: HCI: version 5.4 (0x0d) revision 0x218f, manufacturer 0x0059
[00:00:00.019,836] <inf> bt_hci_core: bt_dev_show_info: LMP: version 5.4 (0x0d) subver 0x218f

[DISCOVERY]: Discovery Mode Fast Scanning
[DISCOVERY]: Discovery Mode Fast Advertising

[CONN]: Connecting to Node:34628, DeviceAddress:D9:55:D0:0F:78:7D (random)
[CONN]: ####### CONNECTED as CENTRAL  MacAddr:D9:55:D0:0F:78:7D (random) #######
[CONN]: CONN_COUNT:1, ConnDataIndex:0, conn_handle:0, k_uptime_get_32():2745
[DISCOVERY]: Discovery Mode Slow Scanning
[CONN]: MTU exchange done

èONN]: ####### CONNECTED as PERIPHERAL,  MacAddr:FA:8F:B8:34:60:23 (random) #######
[CONN]: CONN_COUNT:2, ConnDataIndex:1, conn_handle:9, k_uptime_get_32():6873
[DISCOVERY]: Discovery Mode Slow Scanning

[CONN]: Force disconnecting Node:34628, conn->handle:0
[CONN]: ####### DISCONNECTED Reason: 22  MacAddr:D9:55:D0:0F:78:7D (random) #######
[CONN]: CONN_COUNT:1, conn_handle:0, conn->state:0, k_uptime_get_32():6977

[RECONN]:Reconnection Nodeid:34628, Addr:D9:55:D0:0F:78:7D (random)
[CONN]: Connecting to Node:34628, DeviceAddress:D9:55:D0:0F:78:7D (random)
[00:00:06.980,743] <wrn> bt_conn: bt_conn_exists_le: Found valid connection (0x20001aa0) with address D9:55:D0:0F:78:7D (random) in disconnected state
[ERROR]: Create conn failed (err -22)

In the provided logs, you can observe the connection and disconnection sequences.

Initially, I connected to the device with the address D9:55:D0:0F:78:7D as a master. Then, I connected to the device with the address FA:8F:B8:34:60:23 as a peripheral.

Afterward, I disconnected the first device, D9:55:D0:0F:78:7D, and received a disconnection event indicating that the state is disconnected.

However, when I attempted to reconnect to the last disconnected device, an error occurred stating, "Found valid connection (0x20001aa0) with address D9:55:D0:0F:78:7D (random) in disconnected state."

[Vidar Berg]

AKV said:

However, when I attempted to reconnect to the last disconnected device, an error occurred stating, "Found valid connection (0x20001aa0) with address D9:55:D0:0F:78:7D (random) in disconnected state."

Where does your application attempt to reconnect, is it within the disconnected callback, or right after?

[AKV]

Hi,

Thanks for the response.

I was retrying the disconnected callback. Now, I've added a flag to the disconnect callback, I will check the disconnect flag and initiate the connection from a separate thread, rather than reconnecting from the disconnect callback.

This approach has significantly reduced the failure rate, but occasionally the error "Found valid connection (0x20001aa0) with address D9:55:D0:0F:78:7D (random) in disconnected state" still occurs.

I've observed that there are occasional connectivity issues as well,

1. Failed to connect to D9:55:D0:0F:78:7D (random) with ERROR (2).

2. Post connection the issue "MTU exchange failed (err 14)" occurs and then disconnect.