6. Configuration options to optimize RAM and Flash

6.1 Overview

There are several configuration options available to optimize Flash and RAM storage. The following list highlights key options that significantly increase the free DRAM, heap, and reduce the flash footprint.

For more optimizations, we’ve also listed the reference links to esp-idf’s optimization guide.

6.2 Configurations

6.2.1 Test Environment setup

All numbers mentioned below are collected in the following environment:

Note

  • These numbers may vary slightly in a different environment.

  • All numbers are in bytes

  • As we are using BLE only for commissioning, BLE memory is freed post commissioning, hence there is an increase in the free heap post commissioning. (CONFIG_USE_BLE_ONLY_FOR_COMMISSIONING=y)

  • After building an example, some DRAM will be utilized, and the remaining DRAM will be allocated as heap. Therefore, a direct increase in the free DRAM will reflect as an increase in free heap.

6.2.2 Default Configuration

We have used the default light example here, and below listed are the static and dynamic sizes.

Static memory stats

Size

Decreased by

Used D/IRAM

179487

–

Used Flash

1576436

–
Dynamic memory stats

Free Heap

Increased by

On Bootup

44256

–

Post Commissioning

77976

–

6.2.3 Disable the chip-shell

Console shell is helpful when developing/debugging the application, but may not be necessary in production. Disabling the shell can save space. Disable the below configuration option.

CONFIG_ENABLE_CHIP_SHELL=n
Static memory stats

Size

Decreased by

Used D/IRAM

178695

792

Used Flash

1521816

54620
Dynamic memory stats

Free Heap

Increased by

On Bootup

54136

9880

Post Commissioning

87592

9616

6.2.4 Adjust the dynamic endpoint count

The default dynamic endpoint count and default device type count is 16, which may be excessive for a normal application creating only 2 endpoints. eg: light, only has two endpoints, one for root endpoint and one for actual light. Adjusting this to a lower value, corresponding to the actual number of endpoints the application will create, can save DRAM.

Here, we have set the dynamic endpoint count and device type count to 2. Increase in the DRAM per endpoint/count is ~550 bytes.

CONFIG_ESP_MATTER_MAX_DYNAMIC_ENDPOINT_COUNT=2
CONFIG_ESP_MATTER_MAX_DEVICE_TYPE_COUNT=2
Static memory stats

Size

Decreased by

Used D/IRAM

172859

6628

Used Flash

1576048

388
Dynamic memory stats

Free Heap

Increased by

On Bootup

51020

6764

Post Commissioning

84208

6232

6.2.5 Use the newlib nano formatting

This optimization saves approximately 25-50K of flash, depending on the target. In our case, it results in a flash reduction of 47 KB.

Additionally, it lowers the high watermark of task stack for functions that call printf() or other string formatting functions. Fore more details please take a look at esp-idf’s newlib nano formatting guide.

CONFIG_NEWLIB_NANO_FORMAT=y
Static memory stats

Size

Decreased by

Used D/IRAM

179487

0

Used Flash

1529228

47208
Dynamic memory stats

Free Heap

Increased by

On Bootup

46164

1908

Post Commissioning

79616

1640

6.2.6 BLE Optimizations

Since most devices will primarily operate as BLE peripherals and typically won’t need more than one connection (especially if it’s just a Matter app), we can optimize by reducing the maximum allowed connections, thereby saving DRAM. Additionally, given the peripheral nature of these devices, we can disable the central and observer roles, for further optimization. In current implementation, BLE is disabled once commissioning succeeds, so these optimizations do not contribute to free heap post-commissioning.

Below are the configuration options that can be set to achieve these optimizations.

CONFIG_NIMBLE_MAX_CONNECTIONS=1
CONFIG_BTDM_CTRL_BLE_MAX_CONN=1
CONFIG_BT_NIMBLE_MAX_CONNECTIONS=1
CONFIG_BT_NIMBLE_ROLE_CENTRAL=n
CONFIG_BT_NIMBLE_ROLE_OBSERVER=n
CONFIG_BT_NIMBLE_MAX_BONDS=2
CONFIG_BT_NIMBLE_MAX_CCCDS=2
CONFIG_BT_NIMBLE_SECURITY_ENABLE=n
CONFIG_BT_NIMBLE_50_FEATURE_SUPPORT=n
CONFIG_BT_NIMBLE_WHITELIST_SIZE=1
CONFIG_BT_NIMBLE_GATT_MAX_PROCS=1
CONFIG_BT_NIMBLE_MSYS_1_BLOCK_COUNT=10
CONFIG_BT_NIMBLE_MSYS_1_BLOCK_SIZE=100
CONFIG_BT_NIMBLE_MSYS_2_BLOCK_COUNT=4
CONFIG_BT_NIMBLE_MSYS_2_BLOCK_SIZE=320
CONFIG_BT_NIMBLE_ACL_BUF_COUNT=5
CONFIG_BT_NIMBLE_HCI_EVT_HI_BUF_COUNT=5
CONFIG_BT_NIMBLE_HCI_EVT_LO_BUF_COUNT=3
CONFIG_BT_NIMBLE_ENABLE_CONN_REATTEMPT=n
Static memory stats

Size

Decreased by

Used D/IRAM

177753

1734

Used Flash

1552372

24064
Dynamic memory stats

Free Heap

Increased by

On Bootup

54096

9840

Post Commissioning

77728

-248

6.2.7 Configuring logging event buffer

Matter events serve as a historical record, stored in chronological order in the logging event buffer. By reducing the buffer size we can potentially save the DRAM. However, it’s important to note that this reduction could lead to the omission of events.

For instance, reducing the critical log buffer from 4K to 256 bytes could save 3K+ DRAM, but it comes with the trade-off of potentially missing critical events.

CONFIG_EVENT_LOGGING_CRIT_BUFFER_SIZE=256
CONFIG_EVENT_LOGGING_INFO_BUFFER_SIZE=256
CONFIG_EVENT_LOGGING_DEBUG_BUFFER_SIZE=256
CONFIG_MAX_EVENT_QUEUE_SIZE=20

Reduce ESP system event queue size and event task stack size can increase free heap size.

CONFIG_ESP_SYSTEM_EVENT_QUEUE_SIZE=16
CONFIG_ESP_SYSTEM_EVENT_TASK_STACK_SIZE=2048
CONFIG_MAX_EVENT_QUEUE_SIZE=20

Reduce the chip device event queue size can reduce IRAM size usage, lead to free heap increase.

CONFIG_MAX_EVENT_QUEUE_SIZE=20
Static memory stats

Size

Decreased by

Used D/IRAM

174111

5376

Used Flash

1576434

0
Dynamic memory stats

Free Heap

Increased by

On Bootup

51288

7032

Post Commissioning

84868

6892

6.2.8 Relocate certain code from IRAM to flash memory

Relocating certain code from IRAM to flash can reduce IRAM usage, so increase available heap size. However, this may increase execution time.

Note

The options in this section may impact performance. Please perform thorough testing before using them in production.

6.2.8.1 Reduce BLE IRAM usage

Move most IRAM into flash. This will increase the usage of flash and reduce ble performance. Because the code is moved to the flash, the execution speed of the code is reduced. To have a small impact on performance, you need to enable flash suspend (SPI_FLASH_AUTO_SUSPEND).

CONFIG_BT_CTRL_RUN_IN_FLASH_ONLY=y
Static memory stats

Size

Decreased by

Used D/IRAM

159553

19934

Used Flash

1589720

-13284
Dynamic memory stats

Free Heap

Increased by

On Bootup

64044

19788

Post Commissioning

97608

19632

6.2.8.2 Place FreeRTOS functions into Flash

When enabled the selected Non-ISR FreeRTOS functions will be placed into Flash memory instead of IRAM. This saves up to 8KB of IRAM depending on which functions are used.

CONFIG_FREERTOS_PLACE_FUNCTIONS_INTO_FLASH=y
Static memory stats

Size

Decreased by

Used D/IRAM

170409

9078

Used Flash

1585754

-9318
Dynamic memory stats

Free Heap

Increased by

On Bootup

53344

9088

Post Commissioning

86780

8804

6.2.8.3 Place non-ISR ringbuf functions into flash

Place non-ISR ringbuf functions (like xRingbufferCreate/xRingbufferSend) into flash. This frees up IRAM, but the functions can no longer be called when the cache is disabled.

CONFIG_RINGBUF_PLACE_FUNCTIONS_INTO_FLASH=y
Static memory stats

Size

Decreased by

Used D/IRAM

174741

4746

Used Flash

1581604

-5168
Dynamic memory stats

Free Heap

Increased by

On Bootup

48860

4604

Post Commissioning

82444

4468

6.2.8.4 Use esp_flash implementation in ROM

Enable this flag to use new SPI flash driver functions from ROM instead of ESP-IDF. After enable CONFIG_SPI_FLASH_ROM_IMPL, will increase free IRAM. But may miss out on some flash features and support for new flash chips.

CONFIG_SPI_FLASH_ROM_IMPL=y
CONFIG_SPI_MASTER_ISR_IN_IRAM=n
CONFIG_SPI_SLAVE_ISR_IN_IRAM=n
Static memory stats

Size

Decreased by

Used D/IRAM

166798

12689

Used Flash

1573452

2984
Dynamic memory stats

Free Heap

Increased by

On Bootup

56900

12644

Post Commissioning

90204

12228

6.2.8.5 Force the entire heap component to be placed in flash memory

Enable this flag to save up RAM space by placing the heap component in the flash memory Note that it is only safe to enable this configuration if no functions from esp_heap_caps.h or esp_heap_trace.h are called from IRAM ISR which runs when cache is disabled.

CONFIG_HEAP_PLACE_FUNCTION_INTO_FLASH=y
Static memory stats

Size

Decreased by

Used D/IRAM

179487

0

Used Flash

1576436

0
Dynamic memory stats

Free Heap

Increased by

On Bootup

44124

-132

Post Commissioning

77564

-412

6.2.9 Reduce Task Stack Size

Reduce some task stack size can increase free heap size.

CONFIG_ESP_MAIN_TASK_STACK_SIZE=3072
CONFIG_ESP_TIMER_TASK_STACK_SIZE=2048
CONFIG_CHIP_TASK_STACK_SIZE=6144
Static memory stats

Size

Decreased by

Used D/IRAM

179487

0

Used Flash

1576448

0
Dynamic memory stats

Free Heap

Increased by

On Bootup

48204

3948

Post Commissioning

81660

3684

6.2.10 Excluding Unused Matter Clusters

If the cluster implementation source files use a class derived from another class with virtual functions and instantiate a global object of this class, the linker may keep all the related symbols that may be used for this class in the vtable. To eliminate these symbols, you can deselect the unused Matter clusters under → Component config → ESP Matter → Select Supported Matter Clusters. Excluding unused clusters will help reduce flash and memory usage. The default configuration disables all unused clusters.

CONFIG_SUPPORT_ACCOUNT_LOGIN_CLUSTER=n
CONFIG_SUPPORT_ACTIVATED_CARBON_FILTER_MONITORING_CLUSTER=n
CONFIG_SUPPORT_AIR_QUALITY_CLUSTER=n
CONFIG_SUPPORT_APPLICATION_BASIC_CLUSTER=n
CONFIG_SUPPORT_APPLICATION_LAUNCHER_CLUSTER=n
CONFIG_SUPPORT_AUDIO_OUTPUT_CLUSTER=n
CONFIG_SUPPORT_BOOLEAN_STATE_CONFIGURATION_CLUSTER=n
CONFIG_SUPPORT_BRIDGED_DEVICE_BASIC_INFORMATION_CLUSTER=n
CONFIG_SUPPORT_CARBON_DIOXIDE_CONCENTRATION_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_CARBON_MONOXIDE_CONCENTRATION_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_CHANNEL_CLUSTER=n
CONFIG_SUPPORT_CHIME_CLUSTER=n
CONFIG_SUPPORT_COMMISSIONER_CONTROL_CLUSTER=n
CONFIG_SUPPORT_CONTENT_LAUNCHER_CLUSTER=n
CONFIG_SUPPORT_CONTENT_CONTROL_CLUSTER=n
CONFIG_SUPPORT_CONTENT_APP_OBSERVER_CLUSTER=n
CONFIG_SUPPORT_DEVICE_ENERGY_MANAGEMENT_CLUSTER=n
CONFIG_SUPPORT_DEVICE_ENERGY_MANAGEMENT_MODE_CLUSTER=n
CONFIG_SUPPORT_DIAGNOSTIC_LOGS_CLUSTER=n
CONFIG_SUPPORT_DISHWASHER_ALARM_CLUSTER=n
CONFIG_SUPPORT_DISHWASHER_MODE_CLUSTER=n
CONFIG_SUPPORT_MICROWAVE_OVEN_MODE_CLUSTER=n
CONFIG_SUPPORT_DOOR_LOCK_CLUSTER=n
CONFIG_SUPPORT_ECOSYSTEM_INFORMATION_CLUSTER=n
CONFIG_SUPPORT_ELECTRICAL_ENERGY_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_ELECTRICAL_POWER_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_ENERGY_EVSE_CLUSTER=n
CONFIG_SUPPORT_ENERGY_EVSE_MODE_CLUSTER=n
CONFIG_SUPPORT_ENERGY_PREFERENCE_CLUSTER=n
CONFIG_SUPPORT_FAN_CONTROL_CLUSTER=n
CONFIG_SUPPORT_FAULT_INJECTION_CLUSTER=n
CONFIG_SUPPORT_FIXED_LABEL_CLUSTER=n
CONFIG_SUPPORT_FORMALDEHYDE_CONCENTRATION_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_HEPA_FILTER_MONITORING_CLUSTER=n
CONFIG_SUPPORT_ICD_MANAGEMENT_CLUSTER=n
CONFIG_SUPPORT_KEYPAD_INPUT_CLUSTER=n
CONFIG_SUPPORT_LAUNDRY_WASHER_MODE_CLUSTER=n
CONFIG_SUPPORT_LOCALIZATION_CONFIGURATION_CLUSTER=n
CONFIG_SUPPORT_LOW_POWER_CLUSTER=n
CONFIG_SUPPORT_MEDIA_INPUT_CLUSTER=n
CONFIG_SUPPORT_MEDIA_PLAYBACK_CLUSTER=n
CONFIG_SUPPORT_MICROWAVE_OVEN_CONTROL_CLUSTER=n
CONFIG_SUPPORT_MESSAGES_CLUSTER=n
CONFIG_SUPPORT_MODE_SELECT_CLUSTER=n
CONFIG_SUPPORT_NITROGEN_DIOXIDE_CONCENTRATION_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_SAMPLE_MEI_CLUSTER=n
CONFIG_SUPPORT_OCCUPANCY_SENSING_CLUSTER=n
CONFIG_SUPPORT_POWER_TOPOLOGY_CLUSTER=n
CONFIG_SUPPORT_OPERATIONAL_STATE_CLUSTER=n
CONFIG_SUPPORT_OPERATIONAL_STATE_OVEN_CLUSTER=n
CONFIG_SUPPORT_OPERATIONAL_STATE_RVC_CLUSTER=n
CONFIG_SUPPORT_OVEN_MODE_CLUSTER=n
CONFIG_SUPPORT_OZONE_CONCENTRATION_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_PM10_CONCENTRATION_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_PM1_CONCENTRATION_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_PM2_5_CONCENTRATION_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_POWER_SOURCE_CLUSTER=n
CONFIG_SUPPORT_POWER_SOURCE_CONFIGURATION_CLUSTER=n
CONFIG_SUPPORT_PUMP_CONFIGURATION_AND_CONTROL_CLUSTER=n
CONFIG_SUPPORT_RADON_CONCENTRATION_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_REFRIGERATOR_ALARM_CLUSTER=n
CONFIG_SUPPORT_REFRIGERATOR_AND_TEMPERATURE_CONTROLLED_CABINET_MODE_CLUSTER=n
CONFIG_SUPPORT_RVC_CLEAN_MODE_CLUSTER=n
CONFIG_SUPPORT_RVC_RUN_MODE_CLUSTER=n
CONFIG_SUPPORT_SERVICE_AREA_CLUSTER=n
CONFIG_SUPPORT_SMOKE_CO_ALARM_CLUSTER=n
CONFIG_SUPPORT_SOFTWARE_DIAGNOSTICS_CLUSTER=n
CONFIG_SUPPORT_SWITCH_CLUSTER=n
CONFIG_SUPPORT_TARGET_NAVIGATOR_CLUSTER=n
CONFIG_SUPPORT_TEMPERATURE_CONTROL_CLUSTER=n
CONFIG_SUPPORT_THERMOSTAT_CLUSTER=n
CONFIG_SUPPORT_THERMOSTAT_USER_INTERFACE_CONFIGURATION_CLUSTER=n
CONFIG_SUPPORT_THREAD_BORDER_ROUTER_MANAGEMENT_CLUSTER=n
CONFIG_SUPPORT_THREAD_NETWORK_DIRECTORY_CLUSTER=n
CONFIG_SUPPORT_TIME_FORMAT_LOCALIZATION_CLUSTER=n
CONFIG_SUPPORT_TIME_SYNCHRONIZATION_CLUSTER=n
CONFIG_SUPPORT_TIMER_CLUSTER=n
CONFIG_SUPPORT_TVOC_CONCENTRATION_MEASUREMENT_CLUSTER=n
CONFIG_SUPPORT_UNIT_TESTING_CLUSTER=n
CONFIG_SUPPORT_USER_LABEL_CLUSTER=n
CONFIG_SUPPORT_VALVE_CONFIGURATION_AND_CONTROL_CLUSTER=n
CONFIG_SUPPORT_WAKE_ON_LAN_CLUSTER=n
CONFIG_SUPPORT_LAUNDRY_WASHER_CONTROLS_CLUSTER=n
CONFIG_SUPPORT_LAUNDRY_DRYER_CONTROLS_CLUSTER=n
CONFIG_SUPPORT_WIFI_NETWORK_MANAGEMENT_CLUSTER=n
CONFIG_SUPPORT_WINDOW_COVERING_CLUSTER=n
CONFIG_SUPPORT_WATER_HEATER_MANAGEMENT_CLUSTER=n
CONFIG_SUPPORT_WATER_HEATER_MODE_CLUSTER=n
Static memory stats

Size

Decreased by

Used D/IRAM

179487

3736

Used Flash

1576436

36938
Dynamic memory stats

Free Heap

Increased by

On Bootup

44256

3876

Post Commissioning

77976

4164

6.3 References for futher optimizations