nrf5340 audio broadcast sink sync fail when connecting with app through BLE

RE: nrf5340 audio broadcast sink sync fail when connecting with app through BLE

LandyWang — Wed, 04 Nov 2026 01:32:12 GMT

Thanks for your assistance. This method works.

Now I can connect to the app via BLE and sync the source simultaneously, regardless of the order.

RE: nrf5340 audio broadcast sink sync fail when connecting with app through BLE

Vidar Berg — Tue, 03 Nov 2026 10:42:58 GMT

Update: I discussed this with one of the developers who confirmed that this is a bug. It was fixed by Bluetooth: BAP: SD: Notify only bonded devices on reconnect by Thalley · Pull Request #106981 · zeph…. Unfortunately, it has not been back ported to nRF Connect SDK v3.4.x, but they will look into doing that.

In the meantime you may consider one of the following workarounds proposed by the developer:

The suggested workaround in the devzone ticket

 if (internal_state->attr == NULL) {
  return;
 }

Is the simplest solution for the specific issue (i.e. set_receive_state_changed_cb could be called before bt_bap_scan_delegator_register.

Alternative solutions would be to call bt_bap_scan_delegator_register before establishing any connections (which is also idea to do so that new connections can actually discover the service).

RE: nrf5340 audio broadcast sink sync fail when connecting with app through BLE

Vidar Berg — Tue, 03 Nov 2026 09:29:39 GMT

Thanks, knowing that the call is made from set_receive_state_changed_cb() helps narrow down the problem. I will check with the developers who are more familiar with this codebase to get their thoughts. In the meantime, you could try skipping notifications when the attr pointer is NULL.

static void set_receive_state_changed_cb(struct bt_conn *conn, void *data)
{
	struct bass_recv_state_internal *internal_state = data;
	struct bass_recv_state_flags *flags = &internal_state->flags[bt_conn_index(conn)];
	struct bt_conn_info conn_info;
	int err;
	
	if (internal_state->attr == NULL) {
		return;
	}
	...

RE: nrf5340 audio broadcast sink sync fail when connecting with app through BLE

LandyWang — Tue, 03 Nov 2026 03:25:14 GMT

Thank you for your reply.

Now I've added `CONFIG_BT_MAX_CONN` to both `prj.conf` and `overlay-broadcast_sink.conf`. Without connecting to the app via BLE, the broadcast sink can sync with the broadcast source, and after synchronization, it can connect to the app via BLE. However, if it connects to the app via BLE first, it still cannot synchronize with the broadcast source.

In short, currently, synchronizing with the broadcast source first and then connecting to the app via BLE succeeds, but connecting to the app via BLE first and then synchronizing with the broadcast source causes problems.

[quote userid="4240" url="~/f/nordic-q-a/129533/nrf5340-audio-broadcast-sink-sync-fail-when-connecting-with-app-through-ble/572789"]where bt_gatt_is_subscribed() is being called from, do you know?[/quote]

`bt_gatt_is_subscribed` is called from `set_receive_state_changed_cb` in bap_scan_delegator.c.

[quote userid="4240" url="~/f/nordic-q-a/129533/nrf5340-audio-broadcast-sink-sync-fail-when-connecting-with-app-through-ble/572789"]Also, do you get the same error if you keep CONFIG_BT_GATT_ENFORCE_SUBSCRIPTION enabled?[/quote]

If `CONFIG_BT_GATT_ENFORCE_SUBSCRIPTION` is enabled, BLE read/write operations after connecting to the app via BLE will have problems, so I'm not considering enabling it.

RE: nrf5340 audio broadcast sink sync fail when connecting with app through BLE

Vidar Berg — Mon, 02 Nov 2026 11:54:45 GMT

Hello,

The log shows that the assert is raised here because the "attr" pointer is NULL: https://github.com/nrfconnect/sdk-zephyr/blob/bf801e4e3d19e1ffa76164346480cb7734dd2800/subsys/bluetooth/host/gatt.c#L3343 but it doesn't show where bt_gatt_is_subscribed() is being called from, do you know? Also, do you get the same error if you keep CONFIG_BT_GATT_ENFORCE_SUBSCRIPTION enabled?

Best regards,

Vidar