BLE Audio headset with peripheral with 2 different connections

RE: BLE Audio headset with peripheral with 2 different connections

Simonr — Thu, 03 Sep 2026 10:50:34 GMT

I wonder if you can also disable the CONFIG_BT_PER_ADV_SYNC_TRANSFER_RECEIVER and CONFIG_BT_ISO_SYNC_RECEIVER. Please try and see if you get closer to the required size.

Best regards,

Simon

RE: BLE Audio headset with peripheral with 2 different connections

MehdiZ — Wed, 02 Sep 2026 13:27:38 GMT

Hi Simon,

I'm making a peripheral device( not sure if this is true with LE Audio?). it has the following two roles:

1/LE Audio broadcaster sink

2/sends sensor data to a different central via ACL connection

So if I understood correctly, I should be able to deactivate at least the following two configurations:

CONFIG_BT_ISO_CENTRAL=n
CONFIG_BT_ISO_BROADCASTER=n

Best regards,

Mehdi

RE: BLE Audio headset with peripheral with 2 different connections

Simonr — Wed, 02 Sep 2026 12:30:35 GMT

Hi again Mehdi

Are you making a central or peripheral device here? Only one of the roles should be required, and broadcaster or receiver depending on what your application does. You should also be able to lower the usage by a lot by disabling all logging and debugging. Potentially also lowering the max connections, although that won't change too much.

Best regards,

Simon

RE: BLE Audio headset with peripheral with 2 different connections

MehdiZ — Tue, 01 Sep 2026 08:16:02 GMT

Hi,

I'm on sdk 2.6.0

I thought I needed the broadcasting configuration for the audio LE stack , no?

here's my current configuration files hci_ipc.conf:

CONFIG_BT_ISO_PERIPHERAL=y
CONFIG_BT_ISO_CENTRAL=y
CONFIG_BT_ISO_BROADCASTER=y
CONFIG_BT_ISO_SYNC_RECEIVER=y
CONFIG_BT_EXT_ADV=y
CONFIG_BT_PER_ADV_SYNC_TRANSFER_RECEIVER=y
CONFIG_BT_PER_ADV_SYNC_TRANSFER_SENDER=y

CONFIG_BT_CTLR_CONN_ISO_GROUPS=1
CONFIG_BT_CTLR_CONN_ISO_STREAMS=2
CONFIG_BT_CTLR_SYNC_ISO_STREAM_COUNT=2
CONFIG_BT_CTLR_ADV_ISO_SET=1
CONFIG_BT_CTLR_ADV_ISO_STREAM_COUNT=2

# Support two links as a central, or one link as a peripheral
CONFIG_BT_MAX_CONN=4
CONFIG_BT_CTLR_SDC_PERIPHERAL_COUNT=2

# Allow using more than default advertising event length
CONFIG_BT_CTLR_ADV_DATA_LEN_MAX=251

# To present the audio at the right point in time, we need the controller and
# audio clock to be synchronized
CONFIG_MPSL_TRIGGER_IPC_TASK_ON_RTC_START=y
CONFIG_MPSL_TRIGGER_IPC_TASK_ON_RTC_START_CHANNEL=4

# General
CONFIG_DEBUG=n
CONFIG_ASSERT=n
CONFIG_STACK_USAGE=n
CONFIG_THREAD_MONITOR=n
CONFIG_SERIAL=n
CONFIG_CONSOLE=n
CONFIG_PRINTK=n
CONFIG_UART_CONSOLE=n
CONFIG_BOOT_BANNER=n

MCUboot.conf:

CONFIG_SIZE_OPTIMIZATIONS=y

CONFIG_PM=n
CONFIG_MAIN_STACK_SIZE=20480
CONFIG_MBEDTLS_CFG_FILE="mcuboot-mbedtls-cfg.h"

CONFIG_BOOT_SWAP_SAVE_ENCTLV=n

CONFIG_BOOT_UPGRADE_ONLY=n
CONFIG_BOOT_BOOTSTRAP=n

### mbedTLS has its own heap
# CONFIG_HEAP_MEM_POOL_SIZE is not set

### We never want Zephyr's copy of tinycrypt.  If tinycrypt is needed,
### MCUboot has its own copy in tree.
# CONFIG_TINYCRYPT is not set
# CONFIG_TINYCRYPT_ECC_DSA is not set
# CONFIG_TINYCRYPT_SHA256 is not set
CONFIG_SPI=n
CONFIG_SPI_NOR=n
CONFIG_FLASH=y
CONFIG_FPROTECT=y

### Various Zephyr boards enable features that we don't want.
# CONFIG_BT is not set
# CONFIG_BT_CTLR is not set
# CONFIG_I2C is not set

CONFIG_LOG=n
#CONFIG_LOG_MODE_MINIMAL=y # former CONFIG_MODE_MINIMAL
### Ensure Zephyr logging changes don't use more resources
#CONFIG_LOG_DEFAULT_LEVEL=0
### Decrease footprint by ~4 KB in comparison to CBPRINTF_COMPLETE=y
CONFIG_CBPRINTF_NANO=y
#CONFIG_NRF_RTC_TIMER_USER_CHAN_COUNT=0

CONFIG_MAIN_STACK_SIZE=10240
CONFIG_MBEDTLS_CFG_FILE="mcuboot-mbedtls-cfg.h"

CONFIG_FLASH=y
CONFIG_FPROTECT=y
CONFIG_PM=n

CONFIG_BOOT_SWAP_SAVE_ENCTLV=n
CONFIG_BOOT_ENCRYPT_IMAGE=n

CONFIG_BOOT_BOOTSTRAP=n
CONFIG_BOOT_UPGRADE_ONLY=n

### Minimal Configurations ###
CONFIG_BOOT_USE_MIN_PARTITION_SIZE=y
CONFIG_ASSERT=n
CONFIG_ASSERT_VERBOSE=n
CONFIG_BOOT_BANNER=n
CONFIG_CLOCK_CONTROL=n
CONFIG_CONSOLE=n
CONFIG_CONSOLE_HANDLER=n
CONFIG_GPIO=n
CONFIG_KERNEL_MEM_POOL=n
CONFIG_LOG=n
CONFIG_MINIMAL_LIBC_CALLOC=n
CONFIG_MINIMAL_LIBC_MALLOC=n
CONFIG_MINIMAL_LIBC_REALLOCARRAY=n
CONFIG_NCS_SAMPLES_DEFAULTS=n
CONFIG_NO_RUNTIME_CHECKS=y
CONFIG_NRF_RTC_TIMER=n
CONFIG_PRINTK=n
CONFIG_SECURE_BOOT_DEBUG=n
CONFIG_SERIAL=n
CONFIG_SYS_CLOCK_EXISTS=n
CONFIG_UART_CONSOLE=n

# trying out some more (doesn't do much)
CONFIG_MPU=n
CONFIG_ARM_MPU=n
CONFIG_CBPRINTF_NANO=y
CONFIG_CBPRINTF_LIBC_SUBSTS=n
CONFIG_MINIMAL_LIBC=y

# trying out some more (doesn't do anything)
CONFIG_SPI=n
CONFIG_TIMEOUT_64BIT=n
CONFIG_TIMESLICING=n
CONFIG_MINIMAL_LIBC_OPTIMIZE_STRING_FOR_SIZE=y

prj.conf:

#
# Copyright (c) 2022 Nordic Semiconductor ASA
#
# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
#

# nRF5340 Audio
CONFIG_NRF5340_AUDIO=y

CONFIG_SAMPLE_RATE_CONVERTER=y
CONFIG_SAMPLE_RATE_CONVERTER_FILTER_SIMPLE=y

# General
CONFIG_DEBUG=y
CONFIG_DEBUG_INFO=y
CONFIG_ASSERT=y
CONFIG_STACK_USAGE=y
CONFIG_THREAD_RUNTIME_STATS=y
CONFIG_STACK_SENTINEL=y
CONFIG_INIT_STACKS=y

# Uart driver
CONFIG_SERIAL=n

# Logging
CONFIG_LOG=y
CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y
CONFIG_LOG_TAG_MAX_LEN=2
CONFIG_LOG_TAG_DEFAULT="--"
CONFIG_LOG_BACKEND_UART=n
CONFIG_LOG_BACKEND_RTT=y

# Use this for debugging thread usage
#CONFIG_LOG_THREAD_ID_PREFIX=y

# Console related defines
CONFIG_CONSOLE=y
CONFIG_RTT_CONSOLE=y
CONFIG_UART_CONSOLE=n

# Shell related defines
CONFIG_SHELL=n
CONFIG_KERNEL_SHELL=n
CONFIG_USE_SEGGER_RTT=y
## Disable logs on RTT
CONFIG_SHELL_RTT_INIT_LOG_LEVEL_NONE=n
CONFIG_SHELL_BACKEND_RTT=n
CONFIG_SHELL_BACKEND_SERIAL=n
CONFIG_SHELL_VT100_COMMANDS=n
CONFIG_SHELL_VT100_COLORS=n
#CONFIG_SHELL_STACK_SIZE=4096
#CONFIG_SHELL_CMD_BUFF_SIZE=128
## Reduce shell memory usage
CONFIG_SHELL_WILDCARD=n
CONFIG_SHELL_HELP_ON_WRONG_ARGUMENT_COUNT=n
CONFIG_SHELL_STATS=n
CONFIG_SHELL_CMDS=n
CONFIG_SHELL_HISTORY=n

# Turn off default shell commands
CONFIG_I2C_SHELL=n
CONFIG_HWINFO_SHELL=n
CONFIG_CLOCK_CONTROL_NRF_SHELL=n
CONFIG_FLASH_SHELL=n
CONFIG_DEVICE_SHELL=n

# Suppress LOG_ERR messages from sd_check_card_type. Because SPI_SDHC has no card presence method,
# assume card is in slot. Thus error message is always shown if card is not inserted
CONFIG_SD_LOG_LEVEL_OFF=n

# Suppress LOG_INF messages from hci_core
CONFIG_BT_HCI_CORE_LOG_LEVEL_WRN=y

CONFIG_TRANSPORT_BIS=y
CONFIG_NAOX_HW_CODEC_DA7218=y
CONFIG_HW_CODEC_CIRRUS_LOGIC=n

#EEG configs
CONFIG_NRFX_RTC0=y
CONFIG_I2C=y
CONFIG_GPIO=y

CONFIG_BT=y
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_MAX_CONN=4
#CONFIG_BT_ISO_PERIPHERAL=y
CONFIG_BT_MAX_PAIRED=3

CONFIG_HEAP_MEM_POOL_SIZE=4096

# Over-ride various BT settings for extended data packet size
CONFIG_BT_L2CAP_TX_BUF_COUNT=6
CONFIG_BT_BUF_ACL_RX_SIZE=256
CONFIG_BT_BUF_ACL_TX_SIZE=256
CONFIG_BT_L2CAP_TX_MTU=252
CONFIG_BT_CTLR_DATA_LENGTH_MAX=251
CONFIG_BT_USER_DATA_LEN_UPDATE=y
CONFIG_BT_GATT_CLIENT=y
CONFIG_BT_USER_PHY_UPDATE=y
CONFIG_BT_DEVICE_NAME="NaoX dev kit"
CONFIG_BT_DEVICE_NAME_DYNAMIC=y

# This example requires more workqueue stack
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=8192
CONFIG_MAIN_STACK_SIZE=4096
CONFIG_BT_RX_STACK_SIZE=4096
CONFIG_BT_HCI_TX_STACK_SIZE=2048

CONFIG_CBPRINTF_FP_SUPPORT=y

# ADC configuration
# Zephyr ADC layer disabled to give nrfx_saadc exclusive ownership of the SAADC.
# DT properties (oversampling, acquisition-time) are still read via DT_* macros.
CONFIG_ADC=n
CONFIG_NRFX_SAADC=y

# Timer configuration
#CONFIG_NRFX_TIMER0=y
#CONFIG_NRFX_TIMER1=y
CONFIG_NRFX_TIMER2=y

# DPPI for hardware-chained Timer -> SAADC sampling (no CPU on tick)
CONFIG_NRFX_DPPI=y 

#DFU OTA Config
CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_MCUMGR=y
CONFIG_NET_BUF=y
CONFIG_ZCBOR=y
CONFIG_CRC=y
CONFIG_MCUMGR_TRANSPORT_BT=y
CONFIG_MCUMGR_TRANSPORT_BT_CONN_PARAM_CONTROL=y
CONFIG_IMG_MANAGER=y
CONFIG_STREAM_FLASH=y
CONFIG_FLASH_MAP=y
CONFIG_FLASH=y
CONFIG_MCUMGR_GRP_IMG=y
CONFIG_MCUMGR_GRP_OS=y
CONFIG_MCUMGR_GRP_OS_BOOTLOADER_INFO=y
CONFIG_MCUMGR_TRANSPORT_BT_REASSEMBLY=y

RE: BLE Audio headset with peripheral with 2 different connections

Simonr — Tue, 01 Sep 2026 07:35:49 GMT

Okay, you've reduced the size by a lot at least. Let's see if we can help you get it to fit somehow.

I don't know what exactly you've done by now, but reducing the BLE feature set by removing features you don't need should lower the memory usage of the net core noticeably. Anything related to broadcasting (BROADCASTER, BIS, BIG) can be disabled if you haven't already.

Alternatively, not allowing DFU on the NET core might be worth looking into as well, as that will take quite a bit of memory as well.

How does your memory report look at this point? If you upload it we can help you look at what options you have in more specifics.

Best regards,

Simon

RE: BLE Audio headset with peripheral with 2 different connections

MehdiZ — Mon, 31 Aug 2026 08:49:46 GMT

Hi, after trying many configuration options,
My build is still overflowing the network flash by 600 bytes.

I don't suppose that it's possible to put the memory region in the cpu app flash (still plenty of space there) ?

RE: BLE Audio headset with peripheral with 2 different connections

MehdiZ — Thu, 27 Aug 2026 07:37:06 GMT

Hi,

Thank you very much.

I'll look into it and get back to you.

Best regards,

Mehdi

RE: BLE Audio headset with peripheral with 2 different connections

Simonr — Thu, 27 Aug 2026 07:04:06 GMT

Using the Zephyr Footprint and Memory Usage reports and the VS code extension for it you should be able to get a clear view of what is taking space in your application. The LE Audio stack + BLE stack is already taking up a lot, so if you also add DFU and multiple other functionalities you might be getting close to the flash limits of the nRF5340.

We also have documentation here on memory footprint optimization to minimize the footprint of your application. https://nrfconnectdocs.nordicsemi.com/ncs/latest/nrf/test_and_optimize/optimizing/memory.html

Best regards,

Simon

RE: BLE Audio headset with peripheral with 2 different connections

MehdiZ — Wed, 26 Aug 2026 13:22:13 GMT

Thank you very much for your help.

I managed to get it working.

I'm now trying to add DFU over BLE to the build but I'm overflowing my flash.

../arm-zephyr-eabi/bin/ld.bfd: region `FLASH' overflowed by 16668 bytes

I'm using the internal flash as we don't have external memory on our custom hardware.

I've attempted to reduce the size by using the following configurations but I was not successful.

CONFIG_DEBUG=n
CONFIG_ASSERT=n
CONFIG_STACK_USAGE=n
CONFIG_THREAD_MONITOR=n
CONFIG_CONSOLE=n
CONFIG_PRINTK=n
CONFIG_BOOT_BANNER=n
CONFIG_SIZE_OPTIMIZATIONS=y

Do you know other configurations I can disable to reduce the build size?

Best regards,

Mehdi

RE: BLE Audio headset with peripheral with 2 different connections

Simonr — Mon, 24 Aug 2026 06:48:38 GMT

1900 bytes per second should definitely be possible from a Bluetooth LE perspective. You can use the BLE throughput calculator here to get an estimate of how much data you can expect to get on a BLE connection? I assume you also want to do LE Audio here, so you need to account for how much data that will transmit as well.

Best regards,

Simon

RE: BLE Audio headset with peripheral with 2 different connections

MehdiZ — Wed, 19 Aug 2026 09:24:06 GMT

Hi Maria,

Thank you for your answer

I managed to get something working and now we are in the process of evaluating the performance of both connections.

The ACL activity will be transferring 19 Bytes of data every 10ms.

Do you think this is an acceptable amount?

is there some technical documentation available?

Best regards,

Mehdi

RE: BLE Audio headset with peripheral with 2 different connections

Maria Gilje — Wed, 19 Aug 2026 09:10:37 GMT

Hi Mehdi,

It is feasible for the LE Audio receiver to have a connection to another central. The first steps would be to increase the amount of peripheral roles for you custom HW and to make it advertise after connecting to the LE Audio GW. Note that for LE Audio applications, ISO activity is prioritised over ACL activity, so keep this in mind when evaluating how much ACL activity there will be between the phone and the custom HW.

I hope that can get you started for a few days, as I'll be away the rest of this week. When I get back I'll be able to help you on the way with any issues you encounter while expanding the functionality of your application.

Best regards,

Maria

RE: BLE Audio headset with peripheral with 2 different connections

Pallavi Patil — Tue, 18 Aug 2026 15:15:23 GMT

Hie Mehdi,

We are looking into your case and we will update you as soon as possible.

Thanks for your patience.

Regards

Pallavi