nRF53 peripheral cannot accept multiple connections - advertising fails while connected

Question

Using a simple example application, which works on nRF52, but fails on nRF53, using the Nordic Connect SDK:

- nRF53 in peripheral mode

- connectable advertising

- BT_MAX_CON > 1

- Can accept a single connection, but re-enabling advertising fails while connected

- Therefore, cannot accept a second connection.

Curiously, this works fine on nRF52.
Also curiously, this works fine on vanilla Zephyr, instead of NCS (https://github.com/zephyrproject-rtos/zephyr)

The error log on the nRF53 is: (bt_hci_core: opcode 0x200a status 0x09)

[00:00:00.462,249] <dbg> bt_conn: bt_conn_set_state: disconnected -> connecting-adv
[00:00:00.462,249] <dbg> bt_conn: bt_conn_ref: handle 0 ref 1 -> 2
[00:00:00.462,341] <dbg> bt_conn: bt_conn_prepare_events: 
[00:00:00.463,226] <dbg> bt_conn: bt_conn_unref: handle 0 ref 2 -> 1
Updated MTU: TX: 23 RX: 23 bytes
Connected
[00:01:03.034,393] <dbg> bt_conn: bt_conn_ref: handle 0 ref 1 -> 2
[00:01:03.034,393] <dbg> bt_conn: bt_conn_unref: handle 0 ref 2 -> 1
[00:01:03.034,423] <dbg> bt_conn: bt_conn_ref: handle 0 ref 1 -> 2
[00:01:03.034,484] <dbg> bt_conn: bt_conn_set_state: disconnected -> connecting-adv
[00:01:03.034,484] <dbg> bt_conn: bt_conn_ref: handle 0 ref 1 -> 2
[00:01:03.034,576] <dbg> bt_conn: bt_conn_prepare_events: 
[00:01:03.035,308] <wrn> bt_hci_core: opcode 0x200a status 0x09
[00:01:03.035,339] <dbg> bt_conn: bt_conn_set_state: connecting-adv -> disconnected
[00:01:03.035,339] <dbg> bt_conn: bt_conn_unref: handle 0 ref 2 -> 1
[00:01:03.035,369] <dbg> bt_conn: bt_conn_unref: handle 0 ref 1 -> 0
[00:01:03.035,369] <dbg> bt_conn: bt_conn_set_state: connecting-adv -> connected
[00:01:03.039,337] <dbg> bt_conn: bt_conn_set_state: disconnected -> connecting-adv
[00:01:03.039,337] <dbg> bt_conn: bt_conn_ref: handle 0 ref 1 -> 2
[00:01:03.039,428] <dbg> bt_conn: bt_conn_prepare_events: 
[00:01:03.039,428] <dbg> bt_conn: conn_prepare_events: Adding conn 0x200012e8 to poll list
[00:01:03.040,161] <wrn> bt_hci_core: opcode 0x200a status 0x09
[00:01:03.040,191] <dbg> bt_conn: bt_conn_set_state: connecting-adv -> disconnected
[00:01:03.040,191] <dbg> bt_conn: bt_conn_unref: handle 0 ref 2 -> 1
[00:01:03.040,191] <dbg> bt_conn: bt_conn_unref: handle 0 ref 1 -> 0
[00:01:03.040,283] <dbg> bt_conn: bt_conn_prepare_events:

I have attached a minimal sample application, which can reproduce the problem.

The gist of the application is:

static void connected(struct bt_conn *conn, uint8_t err)
{
	if (err) {
		printk("Connection failed (err 0x%02x)\n", err);
	} else {
		printk("Connected\n");
	}
    bt_le_adv_resume(); // or: bt_start_advertising();
}

and CONFIG_BT_MAX_CONN=4 in prj.conf

Here's the full sample:
5037.ble-advertising-while-connect-sample.zip

Einar Thorsrud · Accepted Answer

Hi, 
 The default configuration of the hci_rpmsg (network core image which includes the Bluetooth controller) supports central connections, and when that is enabled the number of peripheral connections is set to 1 (BT_CTLR_SDC_PERIPHERAL_COUNT). 
 You can change this by making a sub-folder in your application folder called "child_image", and putting a file called hci_rpmsg.conf there. This will function as an overlay configuration file, and in there you can put this (with this, the controller will not support any central connections, but 4 peripheral connections): 
 CONFIG_BT_CENTRAL=n
CONFIG_BT_CTLR_SDC_PERIPHERAL_COUNT=4

nRF53 peripheral cannot accept multiple connections - advertising fails while connected

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