Bluetooth connection cache processing

RE: Bluetooth connection cache processing

Amanda Hsieh — Mon, 30 Jun 2025 20:47:06 GMT

Hi,

The error code -12 when attempting to create a connection (e.g., with bt_conn_le_create or similar functions) typically means "Not enough memory" (-ENOMEM). This indicates that the system does not have enough resources (such as heap memory or connection objects) to establish a new connection.

The error code -128 in the context of bt_gatt_dm: GATT discover failed, error: -128 indicates that there is no active BLE connection when the GATT discovery is attempted. This is equivalent to the ENOTCONN error, which means "Not connected." You will encounter this error if you try to perform GATT operations, such as service discovery, without having an established BLE connection to the peer device.

You can refer to the Central Multilink sample, which can scan, connect, and establish multilink connections.

Regards,
Amanda H.

RE: Bluetooth connection cache processing

carefree — Fri, 27 Jun 2025 04:26:08 GMT

Here are my connection parameters:

peripherals:

_API_(int)
_LIB_NAME_(init)()
{
    int err;

    err = bt_enable(NULL);
    if (err)
    {
        return err;
    }

#if defined(CONFIG_BT_CTLR_PHY_CODED)

    struct bt_le_adv_param param =
        BT_LE_ADV_PARAM_INIT(BT_LE_ADV_OPT_CONNECTABLE |
                                 BT_LE_ADV_OPT_EXT_ADV |
                                 BT_LE_ADV_OPT_CODED,
                             BT_GAP_ADV_FAST_INT_MIN_1,
                             BT_GAP_ADV_FAST_INT_MAX_1,
                             NULL);

#elif defined(CONFIG_BT_EXT_ADV)

    struct bt_le_adv_param param =
        BT_LE_ADV_PARAM_INIT(BT_LE_ADV_OPT_CONNECTABLE |
                                 BT_LE_ADV_OPT_EXT_ADV,_LIB_NAME_(inst
                             BT_GAP_ADV_FAST_INT_MIN_1,
                             BT_GAP_ADV_FAST_INT_MAX_1,
                             NULL);

#endif

    err = bt_le_ext_adv_create(&param, NULL, &_LIB_NAME_(inst).adv);

    if (err)
    {
        printk("Failed to create Coded PHY extended advertising set (err %d)\n", err);
        return err;
    }

    err = bt_le_ext_adv_set_data(_LIB_NAME_(inst).adv, ad, ARRAY_SIZE(ad), NULL, 0);
    if (err)
    {
        printk("Failed to set extended advertising data (err %d)\n", err);
        return err;
    }

    err = bt_le_ext_adv_start(_LIB_NAME_(inst).adv, BT_LE_EXT_ADV_START_DEFAULT);
    if (err)
    {
        printk("Failed to start advertising set (err %d)\n", err);
        return err;
    }

    return 0;
}

At the same time, after the connection, change the PHY to CODED:

static void connected(struct bt_conn *conn, uint8_t conn_err)
{
    int err;

    if (conn_err)
    {
        printk("Connection failed, err 0x%02x \n", conn_err);
        _LIB_NAME_(inst).conn = NULL;
        return;
    }

#if defined(CONFIG_BT_CTLR_PHY_CODED)

    const struct bt_conn_le_phy_param preferred_phy = {
        .options = BT_CONN_LE_PHY_OPT_CODED_S8,
        .pref_rx_phy = BT_GAP_LE_PHY_CODED,
        .pref_tx_phy = BT_GAP_LE_PHY_CODED,
    };
    err = bt_conn_le_phy_update(conn, &preferred_phy);
    if (err)
    {
        printk("bt_conn_le_phy_update() returned %d", err);
    }

#endif

    _LIB_NAME_(inst).conn = conn;
}

static void disconnected(struct bt_conn *conn, uint8_t reason)
{
    // if (_LIB_NAME_(inst).config != NULL && _LIB_NAME_(inst).config->callback.connected != NULL)
    // {
    //     _LIB_NAME_(inst).config->callback.connected(false);
    // }
}

central:

  #define INTERVAL_MIN 10
#define INTERVAL_MAX 10
static struct bt_le_conn_param *conn_param = BT_LE_CONN_PARAM(INTERVAL_MIN, INTERVAL_MAX, 0, 400);
  
  struct bt_conn_le_create_param *conn_create_params = BT_CONN_LE_CREATE_PARAM(
        BT_CONN_LE_OPT_NONE,
        BT_GAP_SCAN_FAST_INTERVAL,
        BT_GAP_SCAN_FAST_WINDOW);

    struct bt_le_conn_param *conn_params = BT_LE_CONN_PARAM(
        BT_GAP_INIT_CONN_INT_MIN,
        BT_GAP_INIT_CONN_INT_MAX,
        0,
        100);

RE: Bluetooth connection cache processing

carefree — Fri, 27 Jun 2025 04:10:29 GMT

After making the modifications, the results were indeed quite satisfactory. However, there are still some other issues that I would like to ask you about. Here is my debugging log:

connect [E4], rssi: -37 phy: 1.
[connected] Connect success.
connect [E4], ret: 1.
[E4]: Send Hello.
[E4]: Send Check Mode.
[E4]: Config Mode.
connect [8F], rssi: -45 phy: 1.
[00:00:07.392,883] [1;33m<wrn> bt_hci_core: opcode 0x2043 status 0x0d [0m
Create connection err: -12.
connect [95], ret: 0.
error: 3.
connect [10], rssi: -50 phy: 1.
[00:00:08.456,329] [1;33m<wrn> bt_hci_core: opcode 0x2043 status 0x0d [0m
Create connection err: -12.
connect [95], ret: 0.
error: 3.
connect [8F], rssi: -45 phy: 1.
[00:00:09.491,851] [1;33m<wrn> bt_hci_core: opcode 0x2043 status 0x0d [0m
Create connection err: -12.
connect [95], ret: 0.
error: 3.
connect [D3], rssi: -42 phy: 1.
[00:00:10.545,196] [1;33m<wrn> bt_hci_core: opcode 0x2043 status 0x0d [0m
Create connection err: -12.
connect [95], ret: 0.
error: 3.
connect [10], rssi: -51 phy: 1.
[00:00:11.610,595] [1;33m<wrn> bt_hci_core: opcode 0x2043 status 0x0d [0m
Reset BLE......

1.This situation occurred when several devices were attempting to connect simultaneously. From the log, it can be seen that except for the first connected device, all the other devices seemed to have failed to connect. What could be the reason for this?

[00:00:19.576,416] [1;33m<wrn> bt_hci_core: Connection creation timeout triggered[0m
[connected] Connect error: 2.
connect [6C], ret: 0.
error: 3.
connect [46], rssi: -45 phy: 1.
[connected] Connect success.

[00:00:51.086,395] [1;31m<err> bt_gatt_dm: GATT discover failed, error: -128.[0m
error: 5.

2.Sometimes such situations occur as well. Could this be due to poor communication quality? Can I optimize some configuration parameters to reduce the occurrence of these two types of errors?

RE: Bluetooth connection cache processing

Amanda Hsieh — Thu, 26 Jun 2025 16:07:31 GMT

Hi,

[quote user=""]1. Sometimes it is impossible to search for any device. This situation usually occurs during the transition from Coded to 2M phy.[/quote]

It seems resource exhaustion or stack instability due to improper cleanup after disconnects or failed connections.

[quote user=""]2. Due to some communication abnormalities, the device resources were not properly released, resulting in bt_conn_le_create returning -12.[/quote]

bt_conn_le_create returning -12 , which typically maps to -ENOMEM means out of memory/resources.

In your disconnect callback, I suggest always calling bt_conn_unref() on the connection object. If you store connection pointers elsewhere, ensure you manage their reference counts correctly. For multilink, you also need to ensure that the CONFIG_BT_MAX_CONN and CONFIG_BT_CTLR_SDC_PERIPHERAL_COUNT are the number of concurrent connections you need, and increase CONFIG_HEAP_MEM_POOL_SIZE accordingly. See my colleague's explanation in this post.

Regards,
Amanda H.

RE: Bluetooth connection cache processing

carefree — Thu, 26 Jun 2025 10:03:48 GMT

In prj.conf, I set CONFIG_BT_MAX_CONN to 1, which can trigger this issue more quickly.