Optimizing memory usage in Matter applications

You can use different approaches to optimizing the memory usage of your Matter application, both on the nRF Connect SDK side and in the Matter SDK.

Reducing memory usage on the nRF Connect SDK side

See the Memory footprint optimization guide for information about how to reduce memory usage for the nRF Connect SDK generally and for specific subsystems in particular, including Bluetooth® LE, Matter, and Thread.

Cutting off log regions for Matter SDK modules

The Matter SDK, included in the nRF Connect SDK as one of the submodule repositories using a dedicated Matter fork, provides a custom mechanism for optimizing memory usage in a Matter application. This solution defines a series of logging modules, each of which is a logical section of code that is a source of log messages and can include one or more files. For the complete list of modules, see the Matter SDK’s LogModule enumeration.

You can reduce the memory usage of each of these modules in the following ways:

• Define a custom logging level for each module by setting one of the Matter SDK logging levels (Error, Progress, Detail, or Automation) in src/chip_project_config.h, located in your application’s directory. For example, the following snippet shows the Bluetooth LE module set to logging at the Detail level:

  CHIP_CONFIG_LOG_MODULE_Ble_DETAIL 1
  

• Turn off logging for any of the modules by setting its respective enabler to 0 in the Matter SDK’s LogModule enumeration. For example, the following snippet shows the Bluetooth LE module cut off from logging its entries:

  CHIP_CONFIG_LOG_MODULE_Ble 0
  

Enabling Link Time Optimization (LTO)

You can reduce the memory usage of your Matter application by enabling Link Time Optimization (LTO).

LTO is an advanced compilation technique that performs optimization across all compiled units of an application at the link stage, rather than within each unit separately.

To enable LTO, set the CONFIG_LTO and CONFIG_ISR_TABLES_LOCAL_DECLARATION Kconfig options to y.

Note

Support for Link Time Optimization is experimental.

Profiling memory in Matter applications

This section offers useful commands for measuring usage of stacks, heaps, and Zephyr settings, and Kconfig options for configuring their memory size. Measuring memory usage allows you to adjust these values according to your project’s requirements.

Measuring memory usage

You can obtain the current memory statistics from the device using Kconfig options and UART shell commands. To do this, set the CONFIG_CHIP_MEMORY_PROFILING global Matter memory profiling Kconfig to y. This activates all the other necessary Kconfig options and enables all UART shell commands for measuring memory usage. Alternatively, you can enable each option separately.

The Kconfig option enables the following functionalities on the Matter device:

• Matter Settings shell commands by setting the CONFIG_NCS_SAMPLE_MATTER_SETTINGS_SHELL Kconfig option to y.

• Using CLI in nRF Connect examples by setting the CONFIG_CHIP_LIB_SHELL Kconfig option to y.

• Zephyr Kernel commands by setting the CONFIG_KERNEL_SHELL Kconfig option to y.

• Zephyr Settings shell by setting the CONFIG_SETTINGS_SHELL Kconfig option to y.

• OpenThread shell by setting the CONFIG_OPENTHREAD_SHELL Kconfig option to y if you build the Matter over Thread variant.

• Matter statistics shell by setting the CONFIG_CHIP_STATISTICS Kconfig option to y.

All the functionalities listed below are automatically enabled if the Matter memory profiling Kconfig option is activated. However, you can also find the specific Kconfig options required for each functionality to enable them separately.

Heap usage and Matter-related statistics

You can measure heap usage by monitoring peak usage. To do this, you need to set the following in your application prj.conf file:

 CONFIG_SHELL=y
 CONFIG_CHIP_STATISTICS=y
 CONFIG_CHIP_MALLOC_SYS_HEAP_WATERMARKS_SUPPORT=y
 CONFIG_CHIP_MALLOC_SYS_HEAP=y
 CONFIG_SYS_HEAP_RUNTIME_STATS=y

To monitor peak usage, you first reset the current peak measurement, then read the peak usage, perform some operations on the device, and read the peak usage again. The difference between the initial and subsequent peak values indicates the number of bytes dynamically allocated by all operations performed by the device during that interval. This method allows you to check for memory leaks or determine the amount of memory specific operations dynamically allocate but some objects may be also destroyed in the meantime, so to obtain the most accurate values the intervals should be as small as possible. By using these results, you can adjust the maximum heap size for your application, thereby optimizing RAM usage for other purposes.

To measure the heap usage, complete the following steps:

1. Clear the current peak values:

   uart:~$ matter stat reset
   

2. Read the current peak values:

   uart:~$ matter stat peak
   

   As a result you will get the following log:

   Packet Buffers: 0
   Timers: 2
   TCP endpoints: 0
   UDP endpoints: 1
   Exchange contexts: 0
   Unsolicited message handlers: 5
   Platform events: 1
   Heap allocated bytes: 208
   

   The value for Heap allocated bytes shows the current peak usage. In addition to heap statistics, you can also obtain other information about the Matter stack from this command.

3. Perform some operations on your device.

4. Read the current peak values using the matter stat peak command again.

   The difference between the current Heap allocated bytes value and the value in Step 2 shows the heap usage.

Non-Volatile Storage (NVS) Settings usage

You can measure the NVS Settings usage by monitoring peak and current usage. To do this, you need to set the following in your application prj.conf file:

 CONFIG_SHELL=y
 CONFIG_NCS_SAMPLE_MATTER_SETTINGS_SHELL=y
 CONFIG_SHELL_MINIMAL=n
 CONFIG_SETTINGS_SHELL=y

The NVS Settings usage may change during the device’s lifetime. The settings_storage partition can only be changed by reflashing the Matter device. This means that it cannot be altered through DFU (Device Firmware Update). Because of this, you need to be careful when setting the partition, and should allocate some free space to ensure that it can accommodate more data in the future. The data used within this partition may increase with updates to Matter and the nRF Connect SDK.

If this functionality is enabled, you can use Matter Settings shell commands.

To see the full list of available commands, use the following UART shell command on your device:

uart:~$ matter_settings

You will see a list of the available commands like this one:

peak      : Print peak settings size in Bytes. This size is reset during
          reboot.
          Usage: matter_settings peak
reset     : Reset peak settings size in Bytes.
            Usage: matter_settings reset
get_size  : Get size of the chosen settings entry.
            Usage: matter_settings get_size <name>
current   : Get current settings size in Bytes.
            Usage: matter_settings current
free      : Get free settings space in Bytes.
            Usage: matter_settings free

Similarly to heap measurements, you can reset the current peak usage value, read the peak value, perform some operations on the device, and read the peak value again to obtain the difference.

1. Reset the peak usage value:

   uart:~$ matter_settings reset
   

2. Measure the peak usage:

   uart:~$ matter_settings peak
   

3. Perform some operations on your device.

4. Read the current peak usage again using the matter_settings peak command again.

   The difference between the current peak value and the value in Step 2 shows the peak usage.

The matter_settings command also allows you also to read the current value of Zephyr settings usage. To read it from the device, use the following UART shell command on your device:

uart:~$ matter_settings current

You can also read the size of a specific settings entry by calling the matter_settings get_size <name> UART shell command on your device. To obtain the name of an entry, you can use the settings list command from the settings UART shell command set.

To read the size of a specific settings entry, complete the following steps:

1. View the list of all available settings:

   uart:~$ settings list
   

   mt/g/im/ec
   mt/g/gdc
   mt/g/gcc
   mt/g/lkgt
   mt/ctr/reboot-count
   mt/cfg/unique-id
   its/0000000000020001
   

2. Choose one of the available keys, for example mt/ctr/reboot-count to read size of the reboot counter.

3. Read the size of the chosen key:

   matter_settings get_size mt/ctr/reboot-count
   

To learn about other settings UART shell commands, use the following UART shell command on your device:

uart:~$ settings

You will see subcommand descriptions like the following:

settings - Settings shell commands
Subcommands:
list    : List all settings in a subtree (omit to list all)
        Usage: settings list [subtree]
read    : Read a specific setting
        Usage: settings read [type] <name>
        type: string or hex (default: hex)
write   : Write to a specific setting
        Usage: settings write [type] <name> <value>
        type: string or hex (default: hex)
delete  : Delete a specific setting
        Usage: settings delete <name>

Note

The Matter Settings shell commands provide only the peak value of the current settings usage. To estimate the space needed for the settings_storage partitions, gather the size of each settings key and decide how often the value is updated during the device’s lifetime.

Stack usage for all threads

You can measure the stack usage by monitoring peak usage of each thread stack. To do this, you need to set the following in your application prj.conf file:

 CONFIG_SHELL=y
 CONFIG_KERNEL_SHELL=y

You can also measure the peak stack usage of each thread running on the Matter device. This measurement can help in setting the proper stack size value and saving RAM space for other stacks or the heap.

To see all statistics for each running thread, use the following UART shell command on your device:

kernel stacks

You will see statistics similar to the following ones, although the number of threads may be different:

0x20011568 CHIP                             (real size 6144):       unused 3952     usage 2192 / 6144 (35 %)
0x200069e8 BT RX WQ                         (real size 1216):       unused 1040     usage  176 / 1216 (14 %)
0x20006930 BT TX                            (real size 1536):       unused 1080     usage  456 / 1536 (29 %)
0x20006d08 rx_q[0]                          (real size 1536):       unused 1384     usage  152 / 1536 ( 9 %)
0x20006e18 openthread                       (real size 4096):       unused 3432     usage  664 / 4096 (16 %)
0x20007be8 ot_radio_workq                   (real size 1024):       unused  848     usage  176 / 1024 (17 %)
0x20006768 shell_uart                       (real size 3200):       unused 2104     usage 1096 / 3200 (34 %)
0x20002580 nrf5_rx                          (real size 1024):       unused  832     usage  192 / 1024 (18 %)
0x2000d510 sysworkq                         (real size 1152):       unused  880     usage  272 / 1152 (23 %)
0x20007b10 MPSL Work                        (real size 1024):       unused  808     usage  216 / 1024 (21 %)
0x2000d3a0 idle                             (real size  320):       unused  272     usage   48 /  320 (15 %)
0x2000d458 main                             (real size 6144):       unused 4584     usage 1560 / 6144 (25 %)
0x20025d00 IRQ 00                           (real size 2048):       unused 1120     usage  928 / 2048 (45 %)

You can read the peak usage measurement for each thread and learn about the total size of the stack, and unused bytes. You can adjust the stack values for your application using estimations based on these measurements.

Configuring memory usage

Most of the Matter samples in the nRF Connect SDK have a safe configuration that assumes a high number of free space for heap, stacks, and settings partition size. After measuring the memory usage, you may want to adjust the memory parameters according to your project’s requirements.

The following sections present a guide on how to adjust specific maximum memory values.

Settings usage

Important

The settings_storage partition can only be changed by reflashing the Matter device. This means that it cannot be altered through DFU (Device Firmware Update). Because of this, you need to be careful when setting the partition, and should allocate some free space to ensure that it can accommodate more data in the future. The data used within this partition may increase with updates to Matter and the nRF Connect SDK.

To adjust the settings usage, you need to modify the pm_static file related to your target board. For example, to modify the settings_storage partition in the Matter Template sample for the nrf52840dk_nrf52840 target, complete the following steps:

1. Locate the pm_static_nrf52840dk_nrf52840.yml in the sample directory

2. Locate the settings_storage partition within the pm_static file.

   For example:

   settings_storage:
       address: 0xf8000
       size: 0x8000
       region: flash_primary
   

3. Modify the size value.

4. Align all other partitions to not overlap any memory regions.

   To learn more about how to configure partitions in the pm_static file, see the Partition Manager documentation.

5. Align the CONFIG_SETTINGS_NVS_SECTOR_COUNT Kconfig option value to the used NVS sectors. Each target in nRF Connect SDK Matter samples uses 4 kB NVS sectors, so you can divide the settings_storage partition size by 4096 (0x1000) to get the value you need to set for the CONFIG_SETTINGS_NVS_SECTOR_COUNT Kconfig option.

To learn more about partitioning, see the Partition layout guide.

Stack sizes for all threads

Each thread has its own Kconfig option to configure the maximum stack size. You can modify Kconfig values to increase or decrease the maximum stack sizes according to your project’s requirements.

The following table presents the possible threads used in a Matter application and the Kconfig options dedicated to setting the maximum stack usage for each of them:

Thread name	Kconfig option	Description of the related stack
CHIP	CONFIG_CHIP_TASK_STACK_SIZE	Matter thread stack. For example, all functions scheduled to be executed from the Matter thread context using the SystemLayer().ScheduleLambda function.
openthread	CONFIG_OPENTHREAD_THREAD_STACK_SIZE	OpenThread thread stack. For Matter over Thread only.
main	CONFIG_MAIN_STACK_SIZE	Application thread stack. For example, all functions scheduled to be executed from the Main thread context using the Nrf::PostTask function.
idle	CONFIG_IDLE_STACK_SIZE	The Idle thread that work while any other thread is not working.
MPSL Work	CONFIG_MPSL_WORK_STACK_SIZE	Multiprotocol Service Layer libraries thread stack. Switching times slots for multi-protocol purposes.
sysworkq	CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE	Zephyr stack. Switching context purposes.
shell_uart	CONFIG_SHELL_STACK_SIZE	Zephyr shell purposes.
BT TX	CONFIG_BT_HCI_TX_STACK_SIZE	Bluetooth LE transmitting thread stack.
nrf5_rx	CONFIG_IEEE802154_NRF5_RX_STACK_SIZE	Bluetooth LE receiving thread stack.
BT RX WQ	CONFIG_BT_RX_STACK_SIZE	Bluetooth LE processing thread stack.
ot_radio_workq	CONFIG_OPENTHREAD_RADIO_WORKQUEUE_STACK_SIZE	IEEE 802.15.4 radio processing thread stack. For Matter over Thread only.
net_mgmt	CONFIG_NET_MGMT_EVENT_STACK_SIZE	Zephyr network management event processing thread stack. For Matter over Wi-Fi only.
wpa_supplicant_main	CONFIG_WIFI_NM_WPA_SUPPLICANT_THREAD_STACK_SIZE	WPA supplicant main thread. Processing Wi-Fi requests and connections. For Matter over Wi-Fi only.
wpa_supplicant_wq	CONFIG_WIFI_NM_WPA_SUPPLICANT_WQ_STACK_SIZE	WPA supplicant work queue thread. Processing Wi-Fi task queue For Matter over Wi-Fi only.
nrf700x_bh_wq	CONFIG_NRF70_BH_WQ_STACK_SIZE	nRF700x Wi-Fi driver work queue.
nrf700x_intr_wq	CONFIG_NRF70_IRQ_WQ_STACK_SIZE	Interrupts processing generated by the nRF700X Wi-Fi radio.
mbox_wq	CONFIG_IPC_SERVICE_BACKEND_RPMSG_WQ_STACK_SIZE	Inter Processor Communication. For multi-processors targets only.

Heap size

The Matter application defines the static size of the heap used by all memory allocations. This configuration ignores the CONFIG_HEAP_MEM_POOL_SIZE Kconfig option value in the application configuration. The static size is determined by the CONFIG_CHIP_MALLOC_SYS_HEAP and CONFIG_CHIP_MALLOC_SYS_HEAP_OVERRIDE Kconfig options. To use a dynamic heap size on your Matter device, set them both to n.

The static heap size means that you can define the maximum heap size for your application by setting the CONFIG_CHIP_MALLOC_SYS_HEAP_SIZE Kconfig value. You can also adjust the heap dedicated for MbedTLS purposes by setting the CONFIG_MBEDTLS_HEAP_SIZE Kconfig option value.

Memory profiling troubleshooting

When you manipulate memory sizes, your device can experience issues and faults. Many of these issues can be caused by incorrect stack or heap configurations. The following can help you troubleshoot if you notice problems with your application:

• Check the name of the thread from which the fault originates.

  If you notice a fault on your Matter device, look at the logs to find the thread that was executing when the error occurred. Sometimes, if there is not enough space in a specific thread, a crash can occur. In such cases, consider increasing the size of the stack dedicated to that thread. Find the thread in the thread and Kconfig option table and change the value of the corresponding Kconfig option in your project configuration.

• The code fails on calloc/malloc functions.

  If your code fails on functions that allocate dynamic memory, try increasing the CONFIG_CHIP_MALLOC_SYS_HEAP_SIZE Kconfig value.

• The code fails while executing some cryptographic operations on an nRF54 Series SoC.

  Currently, most cryptographic operations on the nRF54 Series use the current thread’s stack to store operating data. This means that if a demanding cryptographic operation is executed from a thread context with a stack size that is too small, it will cause an unexpected crash. If you notice such an issue, increase the stack size for the failing thread to verify that the cryptographic operations begin to function properly again.