MCU Built-in Metrics

The Memfault SDK automatically collects a number of metrics without any additional code. This page lists all built-in metrics by platform.

For information on defining your own custom metrics, see the MCU Metrics documentation.

Core Metrics

These metrics are collected on all supported platforms.

Always Collected

Metric	Units	Description	Notes
MemfaultSdkMetric_IntervalMs	ms	Duration of the heartbeat interval	e.g. 3600000; default interval is 1 hour
MemfaultSdkMetric_UnexpectedRebootCount	count	Unexpected reboots since the last heartbeat	e.g. 0; non-zero values indicate unexpected reboots
operational_hours	hours	Operational hours accumulated since the last heartbeat	e.g. 1; increments each heartbeat interval
operational_crashfree_hours	hours	Crash-free operational hours since the last heartbeat	e.g. 1; resets to 0 after a crash

Conditionally Collected

The following core metrics are enabled by setting the corresponding macro in memfault_platform_config.h:

Metric	Units	Description	Enable macro	Notes
sync_successful	count	Successful syncs	MEMFAULT_METRICS_SYNC_SUCCESS 1
sync_failure	count	Failed syncs	MEMFAULT_METRICS_SYNC_SUCCESS 1
sync_memfault_successful	count	Successful Memfault syncs	MEMFAULT_METRICS_MEMFAULT_SYNC_SUCCESS 1
sync_memfault_failure	count	Failed Memfault syncs	MEMFAULT_METRICS_MEMFAULT_SYNC_SUCCESS 1
connectivity_connected_time_ms	ms	Time connected to the network	MEMFAULT_METRICS_CONNECTIVITY_CONNECTED_TIME 1	e.g. 3540000 for ~59 min in a 1-hour interval
connectivity_expected_time_ms	ms	Time the device was expected to be connected	MEMFAULT_METRICS_CONNECTIVITY_CONNECTED_TIME 1	Compare with connectivity_connected_time_ms to compute uptime ratio
battery_soc_pct_drop	%	Battery state-of-charge drop since the last heartbeat	MEMFAULT_METRICS_BATTERY_ENABLE 1	e.g. 5; use with battery_discharge_duration_ms for drain rate
battery_discharge_duration_ms	ms	Duration of battery discharge	MEMFAULT_METRICS_BATTERY_ENABLE 1	Excludes time spent charging
battery_soc_pct	%	Current battery state of charge	MEMFAULT_METRICS_BATTERY_ENABLE 1	e.g. 82
MemfaultSDKMetric_log_dropped_lines	count	Log lines dropped since the last heartbeat	MEMFAULT_METRICS_LOGS_ENABLE 1	Non-zero indicates log buffer pressure
MemfaultSDKMetric_log_recorded_lines	count	Log lines recorded since the last heartbeat	MEMFAULT_METRICS_LOGS_ENABLE 1
uptime_s	s	Device uptime	MEMFAULT_METRICS_UPTIME_ENABLE 1	Monotonically increasing since last POR

The Battery and Connectivity core metrics are also available on all platforms when enabled. See the Core Metrics documentation for details.

FreeRTOS

These metrics are available on FreeRTOS-based platforms. To use them, add the Memfault FreeRTOS port files from ports/freertos/ to your project and include the built-in metric definitions in your memfault_metrics_heartbeat_config.def:

#include "ports/freertos/config/memfault_metrics_heartbeat_freertos_config.def"

ESP-IDF users get these automatically when CONFIG_MEMFAULT_FREERTOS_TASK_RUNTIME_STATS=y.

Metric	Units	Description	Condition	Notes
cpu_usage_pct	% (÷100)	CPU usage percentage	Always when port is included	e.g. 4500 = 45.00%
cpu1_usage_pct	% (÷100)	Core 1 CPU usage percentage	MEMFAULT_FREERTOS_RUNTIME_STATS_MULTI_CORE_SPLIT 1	Dual-core ESP32 etc.
timer_task_stack_free_bytes	bytes	Free bytes in the FreeRTOS timer task stack	MEMFAULT_FREERTOS_COLLECT_TIMER_STACK_FREE_BYTES 1	e.g. 512; low values may indicate stack overflow risk
memory_idle_pct_max	%	Peak idle task stack usage	MEMFAULT_METRICS_THREADS_DEFAULTS 1
memory_tmr_svc_pct_max	%	Peak timer service task stack usage	MEMFAULT_METRICS_THREADS_DEFAULTS 1

Zephyr

Zephyr built-in metrics are organized by the Kconfig option that enables them. Use menuconfig to explore available options under the MEMFAULT submenu.

Default Metrics (CONFIG_MEMFAULT_METRICS_DEFAULT_SET_ENABLE)

Metric	Units	Description	Additional requirement	Notes
cpu_usage_pct	% (÷100)	Total CPU active percentage	CONFIG_THREAD_RUNTIME_STATS=y, Zephyr ≥ 3.0	e.g. 4500 = 45.00%
TimerTaskCpuUsage	%	CPU usage of the timer task	CONFIG_THREAD_RUNTIME_STATS=y	Raw permille value
AllTasksCpuUsage	%	Aggregate CPU usage across all tasks	CONFIG_THREAD_RUNTIME_STATS=y
TimerTaskFreeStack	bytes	Free stack bytes for the timer task	CONFIG_THREAD_STACK_INFO=y	e.g. 384; low values may indicate stack overflow risk
FileSystem_BytesFree	bytes	Free bytes in the filesystem	CONFIG_MEMFAULT_FS_BYTES_FREE_METRIC=y

Networking (CONFIG_MEMFAULT_METRICS_TCP_IP)

Metric	Units	Description	Additional requirement	Notes
net_bytes_received	bytes	Total bytes received	-
net_bytes_sent	bytes	Total bytes sent	-
net_tcp_recv	count	TCP packets received	CONFIG_NET_STATISTICS_TCP=y
net_tcp_sent	count	TCP packets sent	CONFIG_NET_STATISTICS_TCP=y
net_udp_recv	count	UDP packets received	CONFIG_NET_STATISTICS_UDP=y
net_udp_sent	count	UDP packets sent	CONFIG_NET_STATISTICS_UDP=y

Wi-Fi (CONFIG_MEMFAULT_METRICS_WIFI)

Metric	Units	Description	Example	Notes
wifi_connected_time_ms	ms	Time connected to Wi-Fi	3540000	Used to assess connection stability
wifi_disconnect_count	count	Wi-Fi disconnect count	2	Can help identify roaming or signal loss
wifi_standard_version	-	Wi-Fi standard	802.11n	802.11b/g/n/ac/ax
wifi_security_type	-	Security type	WPA2-PSK	Open, WPA2-PSK, WPA3, etc.
wifi_frequency_band	-	Frequency band	2.4	2.4 or 5
wifi_primary_channel	channel	Primary channel ID	6	1–11 (2.4 GHz), 36+ (5 GHz)
wifi_sta_rssi	dBm	Station RSSI	-65	> −70 dBm is generally good
wifi_beacon_interval	TU (1.024 ms)	Beacon interval	100	Typical values: 100 or 102 TU
wifi_dtim_interval	beacon periods	DTIM interval	3	Higher DTIM reduces wake-ups; improves battery at cost of latency
wifi_twt_capable	boolean	TWT (Target Wake Time) capable	1	Power-saving feature introduced in 802.11ax
wifi_tx_rate_mbps	Mbps	TX rate	72	Varies dynamically with signal quality and AP capabilities
wifi_ap_oui	-	OUI of the associated access point	00:1A:2B	Vendor identifier extracted from AP MAC

Bluetooth (CONFIG_MEMFAULT_METRICS_BLUETOOTH)

Metric	Units	Description	Additional requirement	Notes
bt_gatt_mtu_size	octets	GATT MTU size	-	e.g. 247; default is 23; higher = more efficient transfers
bt_connection_remote_info	-	Remote info: [version]:[mfr id].[subversion]	CONFIG_BT_REMOTE_VERSION=y	e.g. 0a:0059.0000
bt_connection_event_count	count	Connection event count	-
bt_connection_interval_us	µs	Connection interval	-	e.g. 45000 (45 ms); range 7.5 ms – 4 s
bt_connection_latency	intervals	Connection latency	-	Number of intervals the peripheral can skip
bt_connection_timeout	10 ms	Supervision timeout	-	e.g. 400 = 4 s; connection dropped if no packet received in this window
bt_connection_rssi	dBm	Connection RSSI	CONFIG_BT_CTLR_CONN_RSSI=y	e.g. −55; > −70 dBm is generally good
bt_connected_time_ms	ms	Time connected	-
bt_disconnect_count	count	Disconnect count	-

CPU Temperature (CONFIG_MEMFAULT_METRICS_CPU_TEMP)

Metric	Units	Description	Example	Notes
thermal_cpu_c	°C (÷10)	CPU temperature	27.5

Memory (CONFIG_MEMFAULT_METRICS_MEMORY_USAGE)

Metric	Units	Description	Additional requirement	Notes
memory_pct_max	% (÷100)	Peak heap utilization since last heartbeat	Zephyr ≥ 3.0	e.g. 4800 = 48.00%
Heap_BytesFree	bytes	Free bytes in the heap	-	e.g. 28672

Thread Stack Defaults (CONFIG_MEMFAULT_METRICS_THREADS_DEFAULTS)

Metric	Units	Description	Additional requirement	Notes
memory_idle_pct_max	%	Peak idle thread stack usage	-	High values (near 100%) indicate near stack overflow
memory_sysworkq_pct_max	%	Peak system work queue stack usage	-
memory_mflt_upload_pct_max	%	Peak Memfault upload thread stack usage	CONFIG_MEMFAULT_PERIODIC_UPLOAD_USE_DEDICATED_WORKQUEUE=y

Boot Time (CONFIG_MEMFAULT_METRICS_BOOT_TIME)

Metric	Units	Description	Example	Notes
boot_time_ms	ms	Boot time	1250	Time from reset to application ready

ESP-IDF

ESP-IDF built-in metrics are enabled via idf.py menuconfig under the Component config → Memfault submenu.

Memory (CONFIG_MEMFAULT_METRICS_MEMORY_USAGE)

Metric	Units	Description	Example	Notes
heap_free_bytes	bytes	Free bytes in the heap	204800	Current free heap
heap_largest_free_block_bytes	bytes	Largest contiguous free block in the heap	131072	Low values may indicate heap fragmentation
heap_allocated_blocks_count	count	Number of currently allocated heap blocks	127
heap_min_free_bytes	bytes	Minimum free bytes ever in the heap	98304	High water mark since boot; indicates worst-case memory pressure
memory_pct_max	% (÷100)	Peak heap utilization since last heartbeat	6200	Divide by 100 for percentage: 62.00%

Wi-Fi (CONFIG_MEMFAULT_ESP_WIFI_METRICS)

Metric	Units	Description	Example	Notes
wifi_connected_time_ms	ms	Time connected to Wi-Fi	3540000	Used to assess connection stability
wifi_sta_min_rssi	dBm	Minimum observed station RSSI	-72	Worst-case signal during the interval; > −70 dBm is generally good
wifi_primary_channel	channel	Primary channel ID	6	1–11 (2.4 GHz), 36+ (5 GHz)
wifi_security_type	-	Security type	WPA2_PSK	Open, WPA2_PSK, WPA3_PSK, etc.
wifi_standard_version	-	Wi-Fi standard	802.11n	802.11b/g/n/ac/ax
wifi_disconnect_count	count	Disconnect count	1	Can help identify roaming or signal loss
wifi_ap_oui	-	OUI of the associated access point	00:1A:2B	Vendor identifier extracted from AP MAC

CPU Temperature (CONFIG_MEMFAULT_METRICS_CPU_TEMP)

Metric	Units	Description	Example	Notes
thermal_cpu_c	°C (÷10)	CPU temperature	452	Divide by 10 for degrees Celsius: 45.2 °C

note

CPU temperature is not supported on the original ESP32.

Chip Info (CONFIG_MEMFAULT_METRICS_CHIP_ENABLE)

Metric	Units	Description	Example	Notes
flash_spi_manufacturer_id	-	24-bit RDID of the SPI flash chip	c84017	c84017 = GigaDevice GD25Q64 8 MiB
flash_spi_total_size_bytes	bytes	Total SPI flash size	8388608	8 MiB
esp_chip_revision	-	Chip model and revision	esp32s3-0.2

Network I/O (CONFIG_MEMFAULT_METRICS_NETWORK_IO)

Requires ESP-IDF ≥ 5.4.0.

Metric	Units	Description	Example	Notes
network_rx_bytes	bytes	Total bytes received over the network	1048576
network_tx_bytes	bytes	Total bytes transmitted over the network	524288

Boot Time (CONFIG_MEMFAULT_METRICS_BOOT_TIME)

Metric	Units	Description	Example	Notes
boot_time_ms	ms	Boot time	2100	Time from reset to application ready

Flash Wear (CONFIG_MEMFAULT_METRICS_FLASH_ENABLE)

Metric	Units	Description	Example	Notes
flash_spi_write_bytes	bytes	Total bytes written to SPI flash	4096	Typical minimum write is one 4 KiB sector
flash_spi_erase_bytes	bytes	Total bytes erased on SPI flash	4096	Flash must be erased before writing

Deep Sleep (CONFIG_MEMFAULT_DEEP_SLEEP_SUPPORT)

These metrics are enabled automatically when CONFIG_MEMFAULT_DEEP_SLEEP_SUPPORT=y and can be individually disabled with CONFIG_MEMFAULT_DEEP_SLEEP_METRICS=n.

Metric	Units	Description	Example	Notes
deep_sleep_time_ms	ms	Time spent in deep sleep	55800000	e.g. ~15.5 hours; use with active_time_ms to compute duty cycle
deep_sleep_wakeup_count	count	Number of deep sleep wakeups	42
active_time_ms	ms	Time spent out of deep sleep	600000

FreeRTOS Task Runtime (CONFIG_MEMFAULT_FREERTOS_TASK_RUNTIME_STATS)

See FreeRTOS metrics above. Enabled on ESP-IDF via CONFIG_MEMFAULT_FREERTOS_TASK_RUNTIME_STATS=y.

LwIP (CONFIG_MEMFAULT_LWIP_METRICS)

Requires TCP_STATS and/or UDP_STATS to be enabled in your LwIP config.

Metric	Units	Description	LwIP requirement	Notes
tcp_tx_count	count	TCP packets sent	TCP_STATS 1
tcp_rx_count	count	TCP packets received	TCP_STATS 1
tcp_drop_count	count	TCP packets dropped	TCP_STATS 1	Non-zero may indicate network congestion
udp_tx_count	count	UDP packets sent	UDP_STATS 1
udp_rx_count	count	UDP packets received	UDP_STATS 1
udp_drop_count	count	UDP packets dropped	UDP_STATS 1	Non-zero may indicate network congestion

MbedTLS (CONFIG_MEMFAULT_MBEDTLS_METRICS)

Metric	Units	Description	Example	Notes
mbedtls_mem_used_bytes	bytes	Current bytes allocated by mbedTLS	12288
mbedtls_mem_max_bytes	bytes	Maximum bytes ever allocated by mbedTLS	36864	Peak typically occurs during TLS handshake

nRF Connect SDK (NCS)

NCS built-in metrics are defined in the Nordic SDK repository (not the Memfault SDK). The Memfault SDK provides the collection implementations. The source of truth for the metric definitions is:

• modules/memfault-firmware-sdk/config/memfault_metrics_heartbeat_extra.def

nRF91 Series - LTE (CONFIG_MEMFAULT_NCS_LTE_METRICS)

Metric	Units	Description	Example	Notes
ncs_lte_time_to_connect_ms	ms	Time to connect to the LTE network	3200	High values may indicate poor coverage or network congestion
ncs_lte_connection_loss_count	count	Number of connection lost events	1
ncs_lte_psm_tau_seconds	s	Assigned PSM tracking area update (TAU) timer	3600
ncs_lte_psm_active_time_seconds	s	Active time for PSM	10	Time modem stays awake after transmitting
ncs_lte_edrx_interval_ms	ms	Assigned eDRX interval	5120
ncs_lte_edrx_ptw_ms	ms	Assigned eDRX paging time window (PTW)	1280
ncs_lte_mode	-	LTE mode	7	0 = None, 7 = LTE-M, 9 = NB-IoT
ncs_lte_on_time_ms	ms	Time the modem is on	360000
ncs_lte_reset_loop_detected_count	count	Times the modem detected a reset loop on the host	0	Non-zero: modem blocks network attaches for 30 min
ncs_lte_modem_fw_version	-	Modem firmware version	nrf9160_1.3.5
ncs_lte_operator	-	Network operator	AT&T
ncs_lte_snr_decibels	dB	Signal-to-noise ratio	15	Higher is better
ncs_lte_rsrp_dbm	dBm	Reference signal received power	-95	−70 to −80 dBm is good; below −100 dBm is poor
ncs_lte_tx_kilobytes	kB	Kilobytes transmitted via the modem	12
ncs_lte_rx_kilobytes	kB	Kilobytes received via the modem	24
ncs_lte_band	-	Assigned frequency band (3GPP enumeration)	2	Maps to 3GPP frequency band; see LTE band reference

nRF91 Series - Stack (CONFIG_MEMFAULT_NCS_STACK_METRICS)

Metric	Units	Description	Example	Notes
ncs_connection_poll_unused_stack	bytes	Free stack bytes in the LTE connection poll thread	512	Low values may indicate stack overflow risk

nRF52 / nRF53 / nRF54 Series - Bluetooth (CONFIG_MEMFAULT_NCS_BT_METRICS)

Metric	Units	Description	Example	Notes
ncs_bt_connection_time_ms	ms	Total Bluetooth connected time	3540000
ncs_bt_connection_count	count	Number of Bluetooth connections	3
ncs_bt_bond_count	count	Number of Bluetooth bonds	1	Persistent across resets

nRF52 / nRF53 / nRF54 Series - Stack (CONFIG_MEMFAULT_NCS_STACK_METRICS)

Metric	Units	Description	Example	Notes
ncs_bt_rx_unused_stack	bytes	Free stack bytes in the Bluetooth RX thread	256	Low values may indicate stack overflow risk
ncs_bt_tx_unused_stack	bytes	Free stack bytes in the Bluetooth TX thread	384	Low values may indicate stack overflow risk

npm13xx Battery (CONFIG_MEMFAULT_NRF_PLATFORM_BATTERY_NPM13XX)

Metric	Units	Description	Example	Notes
battery_voltage	V (÷1000)	Battery voltage	3750	Divide by 1000 for volts: 3.75 V