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 able to spot any obvious problems in the code snippets you posted. Are you able to provide a minimal version of your project here or in a private that would allow me to reproduce the issue on a nRF5340 DK?

[AKV]

Hi,

We have observed an issue related to the missing disconnection event. We were able to reproduce the issue with nRF5340DK.

We're currently using an Event Length (EL) of 2.5 ms and the MTU is set to 247 bytes. During a Data Length Extension (DLE) event, with an EL of 2.5 ms, we can send a maximum of 208 bytes within 894 µs in a single packet.

When we transmit packets smaller than 208 bytes, the issue doesn't occur. However, when the packet size exceeds 208 bytes, the problem happens more frequently. It appears that the issue arises when the link layer splits the packet for transmission.

Here i have attached the sniffer trace.

nrf5340DK_disconnection_event_missing.pcapng

[Vidar Berg]

Hi,

The sniffer trace shows that the peripheral is not responding to the last write command. Do you have logs from the peripheral device when this happens?

[AKV]

Hi,

On the peripheral side, there is no disconnection event, and we are transmitting from both sides.

However, after the other device turns off, the peripheral side indicates that the stack buffer is full and is unable to send packets, yet the disconnection event is not detected. The stack buffer size is set to 30. 

[DISCOVERY]: Discovery Mode Fast Scanning
[DISCOVERY]: Discovery Mode Fast Advertising
[CONN]: ####### CONNECTED as PERIPHERAL,  #######
[CONN]: CONN_COUNT:1, ConnDataIndex:0, conn_handle:99, k_uptime_get_32():59021
[DISCOVERY]: Discovery Mode Slow Scanning
[CONN]: LE data len updated: TX (len: 208 time: 894) RX (len: 208 time: 894)

TX[0] BufferFull:1, ConnHandle:99, InIndex:45, OutIndex:35, StackBufferUserd:10
TX[0] BufferFull:1, ConnHandle:99, InIndex:46, OutIndex:35, StackBufferUserd:11
TX[0] BufferFull:1, ConnHandle:99, InIndex:47, OutIndex:35, StackBufferUserd:12
TX[0] BufferFull:1, ConnHandle:99, InIndex:48, OutIndex:35, StackBufferUserd:13
TX[0] BufferFull:1, ConnHandle:99, InIndex:49, OutIndex:35, StackBufferUserd:14
TX[0] BufferFull:1, ConnHandle:99, InIndex:50, OutIndex:35, StackBufferUserd:15
TX[0] BufferFull:1, ConnHandle:99, InIndex:51, OutIndex:35, StackBufferUserd:16
TX[0] BufferFull:1, ConnHandle:99, InIndex:52, OutIndex:35, StackBufferUserd:17
TX[0] BufferFull:1, ConnHandle:99, InIndex:53, OutIndex:35, StackBufferUserd:18
TX[0] BufferFull:1, ConnHandle:99, InIndex:54, OutIndex:35, StackBufferUserd:19
TX[0] BufferFull:1, ConnHandle:99, InIndex:55, OutIndex:35, StackBufferUserd:20
TX[0] BufferFull:1, ConnHandle:99, InIndex:56, OutIndex:35, StackBufferUserd:21
TX[0] BufferFull:1, ConnHandle:99, InIndex:57, OutIndex:35, StackBufferUserd:22
TX[0] BufferFull:1, ConnHandle:99, InIndex:58, OutIndex:35, StackBufferUserd:23
TX[0] BufferFull:1, ConnHandle:99, InIndex:59, OutIndex:35, StackBufferUserd:24
TX[0] BufferFull:1, ConnHandle:99, InIndex:60, OutIndex:35, StackBufferUserd:25
TX[0] BufferFull:1, ConnHandle:99, InIndex:61, OutIndex:35, StackBufferUserd:26
TX[0] BufferFull:1, ConnHandle:99, InIndex:62, OutIndex:35, StackBufferUserd:27
TX[0] BufferFull:1, ConnHandle:99, InIndex:63, OutIndex:35, StackBufferUserd:28
TX[0] BufferFull:1, ConnHandle:99, InIndex:64, OutIndex:35, StackBufferUserd:29
TX[0] BufferFull:1, ConnHandle:99, InIndex:65, OutIndex:35, StackBufferUserd:30

[Vidar Berg]

Hi,

If you turn off the central device, the peripheral will wait for the supervision timeout timer to expire (was set to 3 seconds the sniffer capture) before it considers the link lost. So, did you wait for the supervision timer to expire? I would also recommend you debug your application to see if any of your threads become blocking/blocked in this scenario.