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  • Case ID: 328899
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nRF5340 BLE Transmission Stack Buffer Overflow

AKV

Hi,

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.

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

I am using the function bt_gatt_write_without_response_cb(). The stack buffer size is set with CONFIG_BT_BUF_ACL_TX_COUNT=30.

The CONFIG_BT_BUF_ACL_TX_COUNT is set to 30, allowing 10 buffers for each connection. I'm using a write complete callback to monitor buffer usage. If the buffer usage for any connection exceeds 10 due to transmission issues, I stop writing to that connection until it is cleared.

If one device connects to two other devices, with one being very close and the other being far away and out of range, the stack buffer becomes full for both connections, even for the nearby device. Why does this issue occur, causing difficulty in sending packets to the nearby device when the other device goes out of range?

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  • 0

    Hi, 

    If one device connects to two other devices, with one being very close and the other being far away and out of range, the stack buffer becomes full for both connections, even for the nearby device. Why does this issue occur, causing difficulty in sending packets to the nearby device when the other device goes out of range?

    When a device is out of range, the BLE stack might still try to resend the data, causing the stack's buffers to fill up. This can prevent new data from being queued for transmission, even for other devices that are within range. 

    Regards,
    Amanda H.

  • 0 in reply to Amanda Hsieh

    Hi,

    Thanks for the response.

    Our project currently runs on the nRF52840 with the nRF5 SDK, and we haven't encountered this issue. We are transitioning to the nRF5340 with the NCS to achieve better performance.

    However, this buffer overflow issue is significantly affecting our device's performance. Since this is a fundamental problem, could you address it on your end? Additionally, can we expect a solution in the next NCS release?

  • 0 in reply to AKV

    Hi, 

    The team said the trace isn't that helpful sadly, and thinks your assumptions are wrong concerning how CONFIG_BT_BUF_ACL_TX_COUNT work. CONFIG_BT_BUF_ACL_TX_COUNT doesn't give 10 buffers per connection because the buffers are shared between all the connections.

    You could try to increase the buffers in the Controller by setting CONFIG_BT_BUF_ACL_RX_COUNT. 

    -Amanda H.

  • 0 in reply to Amanda Hsieh

    Hi

    Amanda Hsieh said:
    CONFIG_BT_BUF_ACL_TX_COUNT doesn't give 10 buffers per connection because the buffers are shared between all the connections.

    I understand that CONFIG_BT_BUF_ACL_TX_COUNT is shared among all connections, so I have set its size to 30. As mentioned earlier, in the application layer, I will write up to 10 for each connection.

    Amanda Hsieh said:
    You could try to increase the buffers in the Controller by setting CONFIG_BT_BUF_ACL_RX_COUNT.

    I have tried to increase the CONFIG_BT_BUF_ACL_RX_COUNT up to 30 but the issue is still there.

    TX[0] BufferFull:0, ConnHandle:2, InIndex:270, OutIndex:270, StackBufferUserd:0
TX[1] BufferFull:0, ConnHandle:0, InIndex:232, OutIndex:232, StackBufferUserd:0
writeCmdTxCmpltCallback index:1 ConnHandle:0, OutIndex:233
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:271
TX[0] BufferFull:0, ConnHandle:2, InIndex:271, OutIndex:271, StackBufferUserd:0
TX[1] BufferFull:0, ConnHandle:0, InIndex:233, OutIndex:233, StackBufferUserd:0
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:272
writeCmdTxCmpltCallback index:1 ConnHandle:0, OutIndex:234
TX[0] BufferFull:0, ConnHandle:2, InIndex:272, OutIndex:272, StackBufferUserd:0
TX[1] BufferFull:0, ConnHandle:0, InIndex:234, OutIndex:234, StackBufferUserd:0
writeCmdTxCmpltCallback index:1 ConnHandle:0, OutIndex:235
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:273
TX[0] BufferFull:0, ConnHandle:2, InIndex:273, OutIndex:273, StackBufferUserd:0
TX[1] BufferFull:0, ConnHandle:0, InIndex:235, OutIndex:235, StackBufferUserd:0
writeCmdTxCmpltCallback index:1 ConnHandle:0, OutIndex:236
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:274
TX[0] BufferFull:0, ConnHandle:2, InIndex:274, OutIndex:274, StackBufferUserd:0
TX[1] BufferFull:0, ConnHandle:0, InIndex:236, OutIndex:236, StackBufferUserd:0
writeCmdTxCmpltCallback index:1 ConnHandle:0, OutIndex:237
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:275
TX[0] BufferFull:0, ConnHandle:2, InIndex:275, OutIndex:275, StackBufferUserd:0
TX[1] BufferFull:0, ConnHandle:0, InIndex:237, OutIndex:237, StackBufferUserd:0
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:276
TX[0] BufferFull:0, ConnHandle:2, InIndex:276, OutIndex:276, StackBufferUserd:0
TX[1] BufferFull:0, ConnHandle:0, InIndex:238, OutIndex:237, StackBufferUserd:1
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:277
TX[0] BufferFull:0, ConnHandle:2, InIndex:277, OutIndex:277, StackBufferUserd:0
TX[1] BufferFull:0, ConnHandle:0, InIndex:239, OutIndex:237, StackBufferUserd:2
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:278
TX[0] BufferFull:0, ConnHandle:2, InIndex:278, OutIndex:278, StackBufferUserd:0
TX[1] BufferFull:0, ConnHandle:0, InIndex:240, OutIndex:237, StackBufferUserd:3
TX[0] BufferFull:0, ConnHandle:2, InIndex:279, OutIndex:278, StackBufferUserd:1
TX[1] BufferFull:0, ConnHandle:0, InIndex:241, OutIndex:237, StackBufferUserd:4
TX[0] BufferFull:0, ConnHandle:2, InIndex:280, OutIndex:278, StackBufferUserd:2
TX[1] BufferFull:0, ConnHandle:0, InIndex:242, OutIndex:237, StackBufferUserd:5
TX[0] BufferFull:0, ConnHandle:2, InIndex:281, OutIndex:278, StackBufferUserd:3
TX[1] BufferFull:0, ConnHandle:0, InIndex:243, OutIndex:237, StackBufferUserd:6
TX[0] BufferFull:0, ConnHandle:2, InIndex:282, OutIndex:278, StackBufferUserd:4
TX[1] BufferFull:0, ConnHandle:0, InIndex:244, OutIndex:237, StackBufferUserd:7
TX[0] BufferFull:0, ConnHandle:2, InIndex:283, OutIndex:278, StackBufferUserd:5
TX[1] BufferFull:0, ConnHandle:0, InIndex:245, OutIndex:237, StackBufferUserd:8
TX[0] BufferFull:0, ConnHandle:2, InIndex:284, OutIndex:278, StackBufferUserd:6
TX[1] BufferFull:0, ConnHandle:0, InIndex:246, OutIndex:237, StackBufferUserd:9
TX[0] BufferFull:0, ConnHandle:2, InIndex:285, OutIndex:278, StackBufferUserd:7
TX[1] BufferFull:1, ConnHandle:0, InIndex:247, OutIndex:237, StackBufferUserd:10
TX[0] BufferFull:0, ConnHandle:2, InIndex:286, OutIndex:278, StackBufferUserd:8
TX[1] BufferFull:1, ConnHandle:0, InIndex:247, OutIndex:237, StackBufferUserd:10
TX[0] BufferFull:0, ConnHandle:2, InIndex:287, OutIndex:278, StackBufferUserd:9
TX[1] BufferFull:1, ConnHandle:0, InIndex:247, OutIndex:237, StackBufferUserd:10
TX[0] BufferFull:1, ConnHandle:2, InIndex:288, OutIndex:278, StackBufferUserd:10
TX[1] BufferFull:1, ConnHandle:0, InIndex:247, OutIndex:237, StackBufferUserd:10
TX[0] BufferFull:1, ConnHandle:2, InIndex:288, OutIndex:278, StackBufferUserd:10
TX[1] BufferFull:1, ConnHandle:0, InIndex:247, OutIndex:237, StackBufferUserd:10

####### DISCONNECTED conn_handle:0 for Reason: 8 #######

writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:279
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:280
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:281
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:282
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:283
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:284
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:285
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:286
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:287
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:288
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:289
writeCmdTxCmpltCallback index:0 ConnHandle:2, OutIndex:290

    I have attached the relevant portion of the application logs. The TX[0] print occurs before sending, and the write complete callback appears when the write complete callback event is received.

    You can see that the write complete callback is received for two connections.

    However, after the connection handle 0 goes out of range, the write complete callback does not come for connection handle 2, even though connection handle 2 is nearby. Once connection handle 0 disconnects, the write complete callback for connection handle 2 comes through.

    The issue is that I am unable to write to the stack buffer for connection handle 2 until the connection handle 0 disconnects.

  • 0 in reply to AKV

    Could you post the full device (app core) logs with:

    CONFIG_BT_GATT_LOG_LEVEL_DBG=y
CONFIG_BT_ATT_LOG_LEVEL_DBG=y
CONFIG_BT_L2CAP_LOG_LEVEL_DBG=y

    Would it also be possible to run your app on a 52840 using NCS to rule out misconfiguration issues between the two 5340 cores?

  • 0 in reply to Jonathan Rico

    Hi,

    Please find the attached log with enabled log.

    CONFIG_BT_GATT_LOG_LEVEL_DBG=y
    CONFIG_BT_ATT_LOG_LEVEL_DBG=y
    CONFIG_BT_L2CAP_LOG_LEVEL_DBG=y

    nRF5340_MultiConnection_BufferOverflow_issue.txt

  • 0 in reply to AKV

    Hi,

    Were you able to verify the log? Are there any updates?

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