Can nRF5340 keep two links simultaneously? One BLE audio link with another nRF5340, one custom BLE link with Smart Phone for configuration

[Junmin]

Hi,

I have kept following BLE audio since the nRF5340 audio DK was available. Recently, we came up with an idea of developing a broadcasting system. While we demoed the idea to potential customer, they required to control the BLE audio nodes with phone app, such as volume up, mute, etc. Is it possible to make a nRF5340 keep connected with 2 devices at the same time, one is on BLE audio, and another is a phone with normal BLE support? If not simultaneously, could be in the same firmware?

Thank you

Junmin

[Karl Ylvisaker]

Hello Junmin,

While we demoed the idea to potential customer, they required to control the BLE audio nodes with phone app, such as volume up, mute, etc. Is it possible to make a nRF5340 keep connected with 2 devices at the same time, one is on BLE audio, and another is a phone with normal BLE support? If not simultaneously, could be in the same firmware?

Do I understand you correctly that you would like to make a broadcaster (BIS), that also connects to a phone over regular BLE connection (ACL connection) in order to control the broadcast's volume etc.?

If I have understood you correctly, the answer is:
Yes - you can add a peripheral or central role to the nRF5340 LE Audio reference application, no problem.
The current controller is able to hold 2 concurrent ACL connections (regular BLE connections) in addition to the 1 or 2 BIS channels.

If I have not understood you correctly, could you share a quick diagram for your intended topology, so that I can better understand what you would like to achieve?

Best regards,
Karl

[Junmin]

Hello Karl,

You understood me pretty well, thank you.

Actually, in addition to broadcaster volume control, we'd like to control receiver volume independently also, but that's the same thing as broadcaster if we can add a peripheral or central role to receivers. I'll try you suggestion next week.

Thank you for positive feedback before weekend.

Have a great weekend

Junmin

[Junmin]

	err = bt_enable(NULL);
	if (err) {
		LOG_INF("Bluetooth init failed (err %d)", err);
		return;
	}

	if (IS_ENABLED(CONFIG_SETTINGS)) {
		settings_load();
	}

	LOG_INF("Bluetooth initialized");

	err = bt_iso_server_register(&iso_server);
	if (err) {
		LOG_INF("Unable to register ISO server (err %d)", err);
		return;
	}

	err = bt_le_adv_start(BT_LE_ADV_CONN, ad, ARRAY_SIZE(ad), NULL, 0);
	if (err) {
		LOG_INF("Advertising failed to start (err %d)", err);
		return;
	}

*** Booting Zephyr OS build v3.3.99-ncs1 ***
HL [00:00:00.257,446] <inf> fw_info: fw_info_app_print: 
         nRF5340 Audio nRF5340 Audio DK cpuapp                      
         NCS base version: 2.4.0                            
         Cmake run : Wed Aug 09 23:30:14 2023
HL [00:00:00.257,446] <inf> fw_info: fw_info_app_print: ------- DEBUG BUILD -------
HL [00:00:00.257,446] <inf> fw_info: fw_info_app_print: HEADSET left device
HL [00:00:00.268,066] <inf> board_version: board_version_valid_check: Compatible board/HW version found: 1.0.0
HL [00:00:00.302,551] <wrn> bt_hci_core: set_flow_control: Controller to host flow control not supported
HL [00:00:00.307,586] <inf> bt_hci_core: bt_dev_show_info: Identity: D4:A5:74:D6:1E:9F (random)
HL [00:00:00.307,617] <inf> bt_hci_core: bt_dev_show_info: HCI: version 5.2 (0x0b) revision 0x0d41, manufacturer 0x07e8
HL [00:00:00.307,617] <inf> bt_hci_core: bt_dev_show_info: LMP: version 5.2 (0x0b) subver 0x0d41
HL [00:00:00.433,502] <inf> ble: mac_print: MAC: 79:DD:C1:19:AE:31 (random)
HL [00:00:00.433,715] <inf> ble: on_bt_ready: Controller version: 3393
HL [00:00:00.527,954] <inf> ble_iso: uart_control_sub_thread: Bluetooth init failed (err -120)
HL [00:00:00.528,228] <inf> cis_headset: advertising_process: Advertising successfully started

[Junmin]

Hello Karl,

I'm still waiting for you suggestions. At the same time, I'm trying to take the following discussion as reference,

 nRF5340 Audio DK: LE Audio and UART2 Concurrently 

Since it's based on NCS 2.20, I'll go down to this version first.

Any comments?

Best Regards

Junmin

[Karl Ylvisaker]

Hello Junmin,

Thank you for your extreme patience with this - I was unfortunately out of office for the first few days of this week due to sickness, but now I am back.

Junmin said:

I checked my code and did some experiments, you are right, I'm attempting to use the same CIS ACL for NUS service. I though a lot and reviewed other people's related questions in DevZone, but still have no idea how to fix it, any suggestions?

I see from your latest log that you receive the -120 error (operation already in progress) from your call to start, but it is hard for me to understand the context from which the bt_enable call was made from the code you have shared alone.
Could you share your full main.c with me, so that I may take a look?

Judging by this error message alone I wonder if you might be calling bt_enable elsewhere, such as in your uart_control_sub_thread? If so, please know that you only need to call bt_enable once in your main().

Junmin said:

At the same time, I'm trying to take the following discussion as reference,

 nRF5340 Audio DK: LE Audio and UART2 Concurrently 

Since it's based on NCS 2.20, I'll go down to this version first.

In this case I would recommend that you instead try the same approach with v2.4, instead of downgrading to v2.2, since there are so many important LE Audio related features and improvements that have been introduced since v2.2.

Best regards,
Karl

[Junmin]

Hello Karl,

Glad to know you are back from sickness!

My main.c is as following, just adding several line on the reference application. I tried to comment out bt_enable in my thread, the error code became -112, address already in use.

/*
 * Copyright (c) 2018 Nordic Semiconductor ASA
 *
 * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
 */

#include <zephyr/kernel.h>
#include <zephyr/debug/stack.h>
#include <zephyr/device.h>
#include <string.h>

#include <zephyr/bluetooth/bluetooth.h>
#include <zephyr/settings/settings.h>
#include <zephyr/zbus/zbus.h>

#include "macros_common.h"
#include "fw_info_app.h"
#include "led.h"
#include "button_handler.h"
#include "button_assignments.h"
#include "nrfx_clock.h"
#include "ble_core.h"
#include "sd_card.h"
#include "board_version.h"
#include "audio_system.h"
#include "channel_assignment.h"
#include "streamctrl.h"
//#include "ble_peripheral_uart.h"
#include "ble_peripheral_iso.h"
static K_SEM_DEFINE(le_audio_ok, 0, 1);

#if defined(CONFIG_AUDIO_DFU_ENABLE)
#include "dfu_entry.h"
#endif

#include <zephyr/logging/log.h>
LOG_MODULE_REGISTER(main, CONFIG_MAIN_LOG_LEVEL);

#if defined(CONFIG_INIT_STACKS)
/* Used for printing stack usage */
extern struct k_thread z_main_thread;
#endif /* defined(CONFIG_INIT_STACKS) */

static atomic_t ble_core_is_ready = (atomic_t) false;
static struct board_version board_rev;

ZBUS_CHAN_DECLARE(button_chan);
ZBUS_CHAN_DECLARE(le_audio_chan);

ZBUS_OBS_DECLARE(button_sub);
ZBUS_OBS_DECLARE(le_audio_evt_sub);

static int hfclock_config_and_start(void)
{
	int ret;

	/* Use this to turn on 128 MHz clock for cpu_app */
	ret = nrfx_clock_divider_set(NRF_CLOCK_DOMAIN_HFCLK, NRF_CLOCK_HFCLK_DIV_1);

	ret -= NRFX_ERROR_BASE_NUM;
	if (ret) {
		return ret;
	}

	nrfx_clock_hfclk_start();
	while (!nrfx_clock_hfclk_is_running()) {
	}

	return 0;
}

static int leds_set(void)
{
	int ret;

	/* Blink LED 3 to indicate that APP core is running */
	ret = led_blink(LED_APP_3_GREEN);
	if (ret) {
		return ret;
	}

#if (CONFIG_AUDIO_DEV == HEADSET)
	enum audio_channel channel;

	channel_assignment_get(&channel);

	if (channel == AUDIO_CH_L) {
		ret = led_on(LED_APP_RGB, LED_COLOR_BLUE);
	} else {
		ret = led_on(LED_APP_RGB, LED_COLOR_MAGENTA);
	}

	if (ret) {
		return ret;
	}
#elif (CONFIG_AUDIO_DEV == GATEWAY)
	ret = led_on(LED_APP_RGB, LED_COLOR_GREEN);
	if (ret) {
		return ret;
	}
#endif /* (CONFIG_AUDIO_DEV == HEADSET) */

	return 0;
}

static int bonding_clear_check(void)
{
	int ret;
	bool pressed;

	ret = button_pressed(BUTTON_5, &pressed);
	if (ret) {
		return ret;
	}

	if (pressed) {
		if (IS_ENABLED(CONFIG_SETTINGS)) {
			LOG_INF("Clearing all bonds");
			bt_unpair(BT_ID_DEFAULT, NULL);
		}
	}
	return 0;
}

static int channel_assign_check(void)
{
#if (CONFIG_AUDIO_DEV == HEADSET) && CONFIG_AUDIO_HEADSET_CHANNEL_RUNTIME
	int ret;
	bool pressed;

	ret = button_pressed(BUTTON_VOLUME_DOWN, &pressed);
	if (ret) {
		return ret;
	}

	if (pressed) {
		channel_assignment_set(AUDIO_CH_L);
		return 0;
	}

	ret = button_pressed(BUTTON_VOLUME_UP, &pressed);
	if (ret) {
		return ret;
	}

	if (pressed) {
		channel_assignment_set(AUDIO_CH_R);
		return 0;
	}
#endif

	return 0;
}

/* Callback from ble_core when the ble subsystem is ready */
void on_ble_core_ready(void)
{
	int ret;

	(void)atomic_set(&ble_core_is_ready, (atomic_t) true);

	if (IS_ENABLED(CONFIG_SETTINGS)) {
		settings_load();

		ret = bonding_clear_check();
		ERR_CHK(ret);
	}

	k_sem_give(&le_audio_ok); 
}

int main(void)
{
	int ret;

	LOG_DBG("nRF5340 APP core started");

	ret = hfclock_config_and_start();
	ERR_CHK(ret);

	ret = led_init();
	ERR_CHK(ret);

	if (IS_ENABLED(CONFIG_ZBUS) && (CONFIG_ZBUS_RUNTIME_OBSERVERS_POOL_SIZE > 0)) {
		ret = zbus_chan_add_obs(&button_chan, &button_sub, K_MSEC(200));
		ERR_CHK(ret);

		ret = zbus_chan_add_obs(&le_audio_chan, &le_audio_evt_sub, K_MSEC(200));
		ERR_CHK(ret);
	}

	ret = button_handler_init();
	ERR_CHK(ret);

	channel_assignment_init();

	ret = channel_assign_check();
	ERR_CHK(ret);

	ret = fw_info_app_print();
	ERR_CHK(ret);

	ret = board_version_valid_check();
	ERR_CHK(ret);

	ret = board_version_get(&board_rev);
	ERR_CHK(ret);

	if (board_rev.mask & BOARD_VERSION_VALID_MSK_SD_CARD) {
		ret = sd_card_init();
		if (ret != -ENODEV) {
			ERR_CHK(ret);
		}
	}

#if defined(CONFIG_AUDIO_DFU_ENABLE)
	/* Check DFU BTN before initialize BLE */
	dfu_entry_check((void *)ble_core_init);
#endif

	/* Initialize BLE, with callback for when BLE is ready */
	ret = ble_core_init(on_ble_core_ready);
	ERR_CHK(ret);

	/* Wait until ble_core/NET core is ready */
	while (!(bool)atomic_get(&ble_core_is_ready)) {
		(void)k_sleep(K_MSEC(100));
	}

	ret = leds_set();
	ERR_CHK(ret);

	ret = streamctrl_start();
	ERR_CHK(ret);
/**/
    /* Don't go any further until BLE is initialized */
    k_sem_take(&le_audio_ok, K_FOREVER);

	ret = uart_start();
	ERR_CHK(ret);

}

Another thing I always wonder is that why I can't find nRF5340 audio DK board with nRF Connect mobile, as you know, I want to do volume control with phone app, scanning devices is the first step.

Thank you for your suggestion to stop trying on v2.2, or I would waste more time on it.

Best Regards

Junmin

[Karl Ylvisaker]

Hello Junmin,

Junmin said:

Glad to know you are back from sickness!

Thank you for saying so! :) 

Junmin said:

My main.c is as following, just adding several line on the reference application. I tried to comment out bt_enable in my thread, the error code became -112, address already in use.

Oh, could you include the code where you have added the nus functionality? I incorrectly assumed that you had this added as a thread towards the end of main.c, but it seems you have that implemented in another file somewhere.

Junmin said:

Another thing I always wonder is that why I can't find nRF5340 audio DK board with nRF Connect mobile, as you know, I want to do volume control with phone app, scanning devices is the first step.

The default nRF5340 LE Audio application will advertise using Direct Advertising in the case that it is already bonded with a peer - could this be the case here?
Also, I think we will need to resolve the current BLE issues in order to ensure that the regular peripheral advertising actually starts in this case, before we look further into this.

Junmin said:

Thank you for your suggestion to stop trying on v2.2, or I would waste more time on it.

No problem at all, I am happy to help! :) 
It would be more productive to instead apply the same approach to your v2.4 based project, instead of downgrading to v2.2.

Best regards,
Karl

[Junmin]

Hello Karl,

You are right, my thread is in another file as following,

/*
 * Copyright (c) 2021 Nordic Semiconductor ASA
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr/types.h>
#include <stddef.h>
#include <string.h>
#include <errno.h>
#include <zephyr/sys/printk.h>
#include <zephyr/sys/byteorder.h>
#include <zephyr/kernel.h>

#include <zephyr/bluetooth/bluetooth.h>
#include <zephyr/bluetooth/hci.h>
#include <zephyr/bluetooth/conn.h>
#include <zephyr/bluetooth/iso.h>
#include <zephyr/settings/settings.h>
#include <zephyr/logging/log.h>

#include "led.h"
#include "macros_common.h"

LOG_MODULE_REGISTER(ble_iso);

#define DEVICE_NAME             "Peripheral"
#define DEVICE_NAME_LEN         (sizeof(DEVICE_NAME) - 1)

static const struct bt_data ad[] = {
	BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
	BT_DATA(BT_DATA_NAME_COMPLETE, DEVICE_NAME, DEVICE_NAME_LEN),
};

static struct k_work_delayable iso_send_work;
static struct bt_iso_chan iso_chan;
static uint16_t seq_num;
static atomic_t iso_tx_pool_alloc;
NET_BUF_POOL_FIXED_DEFINE(tx_pool, 1, BT_ISO_SDU_BUF_SIZE(CONFIG_BT_ISO_TX_MTU), 8,
			  NULL);
#define HCI_ISO_BUF_ALLOC_PER_CHAN 2

static void iso_timer_timeout(struct k_work *work)
{
	int ret;
	static uint8_t buf_data[CONFIG_BT_ISO_TX_MTU];
	struct net_buf *buf;
	static size_t len_to_send = CONFIG_BT_ISO_TX_MTU;
	static bool hci_wrn_printed;

	if (atomic_get(&iso_tx_pool_alloc) >= HCI_ISO_BUF_ALLOC_PER_CHAN) {
		if (!hci_wrn_printed) {
			LOG_WRN("HCI ISO TX overrun");
			hci_wrn_printed = true;
		}
		return;
	}

	hci_wrn_printed = false;

	buf = net_buf_alloc(&tx_pool, K_FOREVER);
	net_buf_reserve(buf, BT_ISO_CHAN_SEND_RESERVE);

	net_buf_add_mem(buf, buf_data, len_to_send);

	atomic_inc(&iso_tx_pool_alloc);
	ret = bt_iso_chan_send(&iso_chan, buf, seq_num++, BT_ISO_TIMESTAMP_NONE);

	if (ret < 0) {
		LOG_INF("Failed to send ISO data (%d)", ret);
		net_buf_unref(buf);
		atomic_dec(&iso_tx_pool_alloc);
	}

	k_work_schedule(&iso_send_work, K_MSEC(10));
}

static void connected(struct bt_conn *conn, uint8_t err)
{
	char addr[BT_ADDR_LE_STR_LEN];

	bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));

	if (err) {
		LOG_INF("Failed to connect to %s (%u)", addr, err);
		return;
	}

	LOG_INF("Connected %s", addr);
}

static void disconnected(struct bt_conn *conn, uint8_t reason)
{
	char addr[BT_ADDR_LE_STR_LEN];

	bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));

	LOG_INF("Disconnected from %s (reason 0x%02x)", addr, reason);
}

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

/** Print data as d_0 d_1 d_2 ... d_(n-2) d_(n-1) d_(n) to show the 3 first and 3 last octets
 *
 * Examples:
 * 01
 * 0102
 * 010203
 * 01020304
 * 0102030405
 * 010203040506
 * 010203...050607
 * 010203...060708
 * etc.
 */
static void iso_print_data(uint8_t *data, size_t data_len)
{
	/* Maximum number of octets from each end of the data */
	const uint8_t max_octets = 3;
	char data_str[35];
	size_t str_len;

	str_len = bin2hex(data, MIN(max_octets, data_len), data_str, sizeof(data_str));
	if (data_len > max_octets) {
		if (data_len > (max_octets * 2)) {
			static const char dots[] = "...";

			strcat(&data_str[str_len], dots);
			str_len += strlen(dots);
		}

		str_len += bin2hex(data + (data_len - MIN(max_octets, data_len - max_octets)),
				   MIN(max_octets, data_len - max_octets),
				   data_str + str_len,
				   sizeof(data_str) - str_len);
	}

	LOG_INF("\t %s", data_str);
}

static void iso_recv(struct bt_iso_chan *chan, const struct bt_iso_recv_info *info,
		struct net_buf *buf)
{
	LOG_INF("Incoming data channel %p len %u", chan, buf->len);
	iso_print_data(buf->data, buf->len);
}

static void iso_connected(struct bt_iso_chan *chan)
{
	LOG_INF("ISO Channel %p connected", chan);
	k_work_reschedule(&iso_send_work, K_MSEC(100));
}

static void iso_disconnected(struct bt_iso_chan *chan, uint8_t reason)
{
	LOG_INF("ISO Channel %p disconnected (reason 0x%02x)", chan, reason);
	k_work_cancel_delayable(&iso_send_work);
	atomic_clear(&iso_tx_pool_alloc);
}

static void iso_sent(struct bt_iso_chan *chan)
{
	atomic_dec(&iso_tx_pool_alloc);
}

static struct bt_iso_chan_ops iso_ops = {
	.recv		= iso_recv,
	.connected	= iso_connected,
	.disconnected	= iso_disconnected,
	.sent = iso_sent,
};

static struct bt_iso_chan_io_qos iso_tx = {
	.sdu = CONFIG_BT_ISO_TX_MTU,
	.path = NULL,
};

static struct bt_iso_chan_qos iso_qos = {
	.tx = &iso_tx,
	.rx = NULL,
};

static struct bt_iso_chan iso_chan = {
	.ops = &iso_ops,
	.qos = &iso_qos,
};

static int iso_accept(const struct bt_iso_accept_info *info,
		      struct bt_iso_chan **chan)
{
	LOG_INF("Incoming request from %p", (void *)info->acl);

	if (iso_chan.iso) {
		LOG_INF("No channels available");
		return -ENOMEM;
	}

	*chan = &iso_chan;

	return 0;
}

static struct bt_iso_server iso_server = {
#if defined(CONFIG_BT_SMP)
	.sec_level = BT_SECURITY_L1,
#endif /* CONFIG_BT_SMP */
	.accept = iso_accept,
};

static struct k_thread uart_control_sub_thread_data;
static k_tid_t uart_control_sub_thread_id;

#define CONFIG_UART_CONTROL_SUB_STACK_SIZE 2048
K_THREAD_STACK_DEFINE(uart_control_sub_thread_stack, CONFIG_UART_CONTROL_SUB_STACK_SIZE);

static void uart_control_sub_thread(void)
{
	int err;

	err = bt_enable(NULL);
	if (err) {
		LOG_INF("Bluetooth init failed (err %d)", err);
		return;
	}

	if (IS_ENABLED(CONFIG_SETTINGS)) {
		settings_load();
	}

	LOG_INF("Bluetooth initialized");

	err = bt_iso_server_register(&iso_server);
	if (err) {
		LOG_INF("Unable to register ISO server (err %d)", err);
		return;
	}

	err = bt_le_adv_start(BT_LE_ADV_CONN, ad, ARRAY_SIZE(ad), NULL, 0);
	if (err) {
		LOG_INF("Advertising failed to start (err %d)", err);
		return;
	}

	LOG_INF("Advertising successfully started");
	k_work_init_delayable(&iso_send_work, iso_timer_timeout);
}

int uart_start(void)
{
	int ret;

	uart_control_sub_thread_id =
		k_thread_create(&uart_control_sub_thread_data, uart_control_sub_thread_stack,
						CONFIG_UART_CONTROL_SUB_STACK_SIZE,
						(k_thread_entry_t)uart_control_sub_thread, NULL, NULL, NULL,
						K_PRIO_PREEMPT(CONFIG_BUTTON_MSG_SUB_THREAD_PRIO), 0, K_NO_WAIT);
	ret = k_thread_name_set(uart_control_sub_thread_id, "UART_CONTROL_SUB");
	ERR_CHK(ret);

	ret = led_blink(LED_APP_1_BLUE);
	ERR_CHK(ret);

	return 0;
}

I have tested the nRF5340 LE Audio application with a Pixel 7, it's no problem to scan, bond and stream from the phone, but not vice versa. Also, at least once,I have scanned and bonded the application with nRF Connect mobile from another phone without BLE audio support, however I can't repeat the phenomenon anyhow, maybe a previous SDK version.

Best regards and have a nice weekend,

Junmin

[Junmin]

Also, I think the key point of my case is to add a peripheral role to the nRF5340 audio application in SDK, which a phone without BLE audio support can scan, bond and communicate with.

Junmin

[Karl Ylvisaker]

Hello Junmin,

Junmin said:

I have tested the nRF5340 LE Audio application with a Pixel 7, it's no problem to scan, bond and stream from the phone, but not vice versa. Also, at least once,I have scanned and bonded the application with nRF Connect mobile from another phone without BLE audio support, however I can't repeat the phenomenon anyhow, maybe a previous SDK version.

I am glad to read that you were able to test this against a Pixel 7 as expected, but I am not quite sure what you mean when you say that it did not work the other way around - does this mean that you wanted the Pixel 7 to function as a peripheral with a nRF5340 Audio DK working as the central/gateway?

If you bond the nRF5340 Audio reference application with another device then it will be using direct advertising to advertise to this specific device again by default, and so it will not be visible to other devices (unless you use a BLE sniffer to see all BLE traffic). Does the device show up again as advertising if you reprogram it? If so, the issue is likely that it is using direct advertising since it is already bonded to the other device.

Junmin said:

Also, I think the key point of my case is to add a peripheral role to the nRF5340 audio application in SDK, which a phone without BLE audio support can scan, bond and communicate with.

Please see the example referenced earlier (and at the last sentence of this comment) for how you can add this to your application.

Junmin said:

You are right, my thread is in another file as following,

Thank you for sharing the code - you do not need to call bt_enable again in your uart_control_sub_thread call since this is already called in your main() startup.
It also seems to me that you are trying to register an iso server in your uart_control_sub_thread, which I am not sure why you would do, if you only wish for the NUS service to run alongside the existing CIS (that you setup in your main() already).

Regarding your code, do you intend for the NUS service to be available alongside the other LE Audio services, or do you intend for it to be a separate connection (potentially to another device) entirely?
In case of the former, which is the impression I have had from your earlier description, you can use this example as a reference regarding how you can add the NUS service to your gateway code.

Best regards,
Karl

[Junmin]

Hello Karl,

As for the Pixel 7 test, I mean the nRF5340 audio DK board works as a BT speaker instead of headset, which can stream audio signal from Pixel 7 to the DK board but can't stream sound back to Pixel 7. The test does nothing with our current application, sorry for making you feel confused.

Thank you for explaining me the direct advertising concept, now I understand what I have observed before.

I intend to use a separate connection to do real time configuration, and made some progress last weekend taking the " Multiple advertising sets' example as reference.

Best Regards

Junmin

[Karl Ylvisaker]

Hello Junmin,

Junmin said:

As for the Pixel 7 test, I mean the nRF5340 audio DK board works as a BT speaker instead of headset, which can stream audio signal from Pixel 7 to the DK board but can't stream sound back to Pixel 7. The test does nothing with our current application, sorry for making you feel confused.

No worries - I will just ask for clarifications if there is somethings that are unclear to me! :) 
I am still not sure that I understand this configuration you describe correctly, unfortunately - could you possibly draw a quick diagram of the configuration you are testing with here? Will the nRF5340 Audio DK be a gateway device that sends a CIS stream to a Pixel 7, or will you use the nRF5340 Audio DK as a headset device that outputs the audio it received from the Pixel 7 to a speaker or similar?

Junmin said:

Thank you for explaining me the direct advertising concept, now I understand what I have observed before.

No problem at all, I am glad to read that this explanation matches the behavior you described.

Junmin said:

I intend to use a separate connection to do real time configuration, and made some progress last weekend taking the " Multiple advertising sets' example as reference.

Do you mean a separate connection between the same devices? If so, why could you not just do these configurations over the ACL that is already established for the CIS? You can add both custom and standard services to the headset/peripheral device, which would function just as it would on a regular non-LE Audio device, or without the CIS in place.

Best regards,
Karl