BLE peripheral with multiple connections

Question

I'm struggling to get a peripheral device to work with two simultaneous connections. I have attached my configuration (for the application) and my connect/disconnect callbacks, with the advertizing data.

I'm advertizingwith BT_LE_ADV_OPT_CONNECTABLE and not with ONE_TIME flag. I understand this should keep adv running until I manually stop it. This is my desired behaviour. Upon the first connection to the device, however, I already get a warning from bt_hci_core <wrn> bt_hci_core: opcode 0x200a status 0x0d. Where 0x0d means CONNECTION REJECTED DUE TO LIMITED RESOURCES. Note that this is different from CONNECTION LIMIT EXCEEDED (0x09) that I read in other posts. I have the feeling that the controller is still somehow allocating only resources for one single peripheral, despite the BT_MA_CONN=2 configuration.
I read in some posts about the CONFIG_BT_CTLR_SDC_PERIPHERAL_COUNT config, which seems to address this, however this should be relevant only in the case where the device is also acting as Central device. I cannot select this config in my application. However, if I check the compiled .config in the hci_ipc application, indeed there I find this configured to 1 and with BT_CENTRAL enabled. I'm now confused on what I should do to get my application running. I don't think I'm expected to modify the hci_ipc sample manually
On a different note, I'm also confused on the purpose of bt_conn_ref() and bt_conn_unref(). They are not always present in the ble samples, and I'm not sure I understand what they are used for (the examples seem to work without them).

Many thanks for the help!

CONFIG_BT=y
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_MAX_CONN=2
# CONFIG_BT_CTLR_SDC_PERIPHERAL_COUNT=2 # this is not selectable in the application?
CONFIG_BT_USER_DATA_LEN_UPDATE=y
CONFIG_BT_USER_PHY_UPDATE=y
CONFIG_BT_GAP_AUTO_UPDATE_CONN_PARAMS=n

static void connected(struct bt_conn *conn, uint8_t code){

    if(code){
        LOG_ERR("Connection failed (code 0x%0x2)", code);
        // bt_conn_unref(conn);
        return;
    }

    conn_count++;
    bt_conn_ref(conn);

    __ASSERT(conn_count < CONFIG_BT_MAX_CONN, "Conn counting error");

    LOG_INF("Connected to Client (code 0x%0x2)", code);

    if(conn_count >= CONFIG_BT_MAX_CONN){
        int err = stop_advertising();
        if(err){
            LOG_ERR("Advertising failed to start (err %d)", err);
        }
    }

    post_event_async(BLE_EVT_CONNECTED);
}

static void disconnected(struct bt_conn *conn, uint8_t code){

    LOG_INF("Disconnected from Client (code 0x%0x2)", code);

    bt_conn_unref(conn);

    conn_count--;

    __ASSERT(conn_count <= CONFIG_BT_MAX_CONN, "Conn counting error");

    int err = start_advertising();
    if(err){
        LOG_ERR("Advertising failed to start (err %d)", err);
    }

    post_event_async(BLE_EVT_DISCONNECTED);
}

BT_CONN_CB_DEFINE(conn_callbacks) = {
	.connected = connected,
	.disconnected = disconnected,
};

static int start_advertising(void){
    struct bt_data ad[] = {
        BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
        BT_DATA_BYTES(BT_DATA_NAME_SHORTENED, CONFIG_BT_DEVICE_NAME),
    };
    return bt_le_adv_start(
        BT_LE_ADV_PARAM(BT_LE_ADV_OPT_CONNECTABLE,
            BT_GAP_ADV_FAST_INT_MIN_2,
            BT_GAP_ADV_FAST_INT_MAX_2,
            NULL), // undirected adv
        ad, ARRAY_SIZE(ad), NULL, 0);
}

PS: I'm using NCS 2.7.0 on nrf5340

Hieu · Accepted Answer

Yaxit said:
I'm not using parent-child image anymore, as this is marked to be deprecated. I'm using the suggested sysbuild approach. The two images are found in separate folders in my build directory.

Interesting that your setup defaulted to use HCI IPC. But no matters, the solution remains the same.

Yaxit said:
I'm not sure how I can configure the netcore image with sysbuild. The HCI_IPC sample is in the zephyr tree, isn't this different from Nordic's softdevice?

The HCI IPC application can work with both the Zephyr Controller and the SoftDevice Controller. While working with NCS, the default controller would be the SoftDevice Controller.

If you need to be extra sure, you can check the .config file in <build dir>/hci_ipc/zephyr to see if CONFIG_BT_LL_SOFTDEVICE or CONFIG_BT_LL_SW_SPLIT is set. If it's the _SOFTDEVICE config that is set, then the SoftDevice Controller is used.

Yaxit said:
I tried to make some sense of it from here but I'm more confused than before :D
docs.nordicsemi.com/.../index.html

You got very close. The method is described in this section: Zephyr application Kconfig fragment and devicetree overlay.

So basically, you create <project dir>/sysbuild/hci_ipc.conf, and put in the configs mentioned in my last reply.

BLE peripheral with multiple connections

Top Replies