NCS/Zephyr peripheral to multiple centrals ECONNREFUSED

[Jason Wright]

For my application I'd like to have my device (nRF5340) be simultaneously (1) a central with a single peripheral connected, and (2) a peripheral with multiple centrals connected.

To facilitate this I want connectable advertising to continue even after the first connection has been established.

I start advertising with:

static const struct bt_data ad[] = {
BT_DATA_BYTES(BT_DATA_GAP_APPEARANCE,
(CONFIG_BT_DEVICE_APPEARANCE >> 0) & 0xff,
(CONFIG_BT_DEVICE_APPEARANCE >> 8) & 0xff),
BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
BT_DATA_BYTES(BT_DATA_UUID16_ALL, BT_UUID_16_ENCODE(BT_UUID_HIDS_VAL)),
};

static const struct bt_data sd[] = {
BT_DATA_BYTES(BT_DATA_NAME_COMPLETE, CONFIG_BT_DEVICE_NAME)
};

...

err = bt_le_adv_start(BT_LE_ADV_CONN, ad, ARRAY_SIZE(ad),
sd, ARRAY_SIZE(sd));

And my prj.conf includes:

CONFIG_BT=y
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_CENTRAL=y
CONFIG_BT_MAX_CONN=8
CONFIG_BT_MAX_PAIRED=8

CONFIG_BT_SMP=y

CONFIG_BT_CONN_CTX=y

CONFIG_BT_SCAN=y
CONFIG_BT_SCAN_FILTER_ENABLE=y
CONFIG_BT_SCAN_UUID_CNT=1

CONFIG_BT_GATT_CLIENT=y
CONFIG_BT_GATT_DM=y

So I have two questions on this:

1. Is there a setting in NCS/Zephyr to have advertising not stop upon connection?
2. I tried manually restarting advertising in the connection callback (by calling bt_le_adv_start with the same parameters again). But bt_le_adv_start returns -ECONNREFUSED, which according to Zephyr docs happens "When connectable advertising is requested and there is already maximum number of connections established in the controller." Why is this the case when I have CONFIG_BT_MAX_CONN=8? Is this a bug?

[Susheel Nuguru]

Is there a setting in NCS/Zephyr to have advertising not stop upon connection?

Not sure if there is, but you can start the advertising again based on role using bt_le_adv_start in the connected event callback that you registered with BT_CONN_CB_DEFINE (EDIT, based on your second question, it seems that you have figured this out already)

I tried manually restarting advertising in the connection callback (by calling bt_le_adv_start with the same parameters again). But bt_le_adv_start returns -ECONNREFUSED, which according to Zephyr docs happens "When connectable advertising is requested and there is already maximum number of connections established in the controller." Why is this the case when I have CONFIG_BT_MAX_CONN=8? Is this a bug?

Assuming that you are using the softdevice controller (SDC) and assuming that you have not changed the default value of CONFIG_SDC_SLAVE_COUNT which is 1, makes the peripheral count set to 1 and the central count set to 7 in this case. If you can set CONFIG_SDC_SLAVE_COUNT=7 in the proj.conf, then you might not get this error.

[Jason Wright]

Thank you for the reply.

It seems that CONFIG_SDC_SLAVE_COUNT is not present in the latest NCS: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/kconfig/search.html?q=CONFIG_SDC_SLAVE_COUNT&check_keywords=yes&area=default

Now it is CONFIG_BT_CTLR_SDC_PERIPHERAL_COUNT: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/kconfig/index.html#CONFIG_BT_CTLR_SDC_PERIPHERAL_COUNT

And it must go in the child image configuration.

With that working, I start getting -EALREADY returned from the call to bt_le_adv_start. And indeed, with the PERIPHERAL_COUNT greater than 1, it seems it's not necessary to manually restart advertising in the connection callback.