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Voltage Wake Configuration
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Boot Voltage Protection
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Voltage Wake (LPCOMP + VBUS)
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Early Boot Register Capture
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Shutdown Reason Tracking
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Architecture
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Early Boot Capture
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Board Implementation
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Voltage Wake Configuration
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References
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< a href = "https://github.com/meshcore-dev/meshcore/edit/main/docs/nrf52_power_management.md" title = "Edit this page" class = "md-content__button md-icon" rel = "edit" >
< svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 24 24" > < path d = "M10 20H6V4h7v5h5v3.1l2-2V8l-6-6H6c-1.1 0-2 .9-2 2v16c0 1.1.9 2 2 2h4zm10.2-7c.1 0 .3.1.4.2l1.3 1.3c.2.2.2.6 0 .8l-1 1-2.1-2.1 1-1c.1-.1.2-.2.4-.2m0 3.9L14.1 23H12v-2.1l6.1-6.1z" / > < / svg >
< / a >
< h1 id = "nrf52-power-management" > nRF52 Power Management< / h1 >
< h2 id = "overview" > Overview< / h2 >
< p > The nRF52 Power Management module provides battery protection features to prevent over-discharge, minimise likelihood of brownout and flash corruption conditions existing, and enable safe voltage-based recovery.< / p >
< h2 id = "features" > Features< / h2 >
< h3 id = "boot-voltage-protection" > Boot Voltage Protection< / h3 >
< ul >
< li > Checks battery voltage immediately after boot and before mesh operations commence< / li >
< li > If voltage is below a configurable threshold (e.g., 3300mV), the device configures voltage wake (LPCOMP + VBUS) and enters protective shutdown (SYSTEMOFF)< / li >
< li > Prevents boot loops when battery is critically low< / li >
< li > Skipped when external power (USB VBUS) is detected< / li >
< / ul >
< h3 id = "voltage-wake-lpcomp-vbus" > Voltage Wake (LPCOMP + VBUS)< / h3 >
< ul >
< li > Configures the nRF52's Low Power Comparator (LPCOMP) before entering SYSTEMOFF< / li >
< li > Enables USB VBUS detection so external power can wake the device< / li >
< li > Device automatically wakes when battery voltage rises above recovery threshold or when VBUS is detected< / li >
< / ul >
< h3 id = "early-boot-register-capture" > Early Boot Register Capture< / h3 >
< ul >
< li > Captures RESETREAS (reset reason) and GPREGRET2 (shutdown reason) before SystemInit() clears them< / li >
< li > Allows firmware to determine why it booted (cold boot, watchdog, LPCOMP wake, etc.)< / li >
< li > Allows firmware to determine why it last shut down (user request, low voltage, boot protection)< / li >
< / ul >
< h3 id = "shutdown-reason-tracking" > Shutdown Reason Tracking< / h3 >
< p > Shutdown reason codes (stored in GPREGRET2):
| Code | Name | Description |
|------|------|-------------|
| 0x00 | NONE | Normal boot / no previous shutdown |
| 0x4C | LOW_VOLTAGE | Runtime low voltage threshold reached |
| 0x55 | USER | User requested powerOff() |
| 0x42 | BOOT_PROTECT | Boot voltage protection triggered |< / p >
< h2 id = "supported-boards" > Supported Boards< / h2 >
< table >
< thead >
< tr >
< th > Board< / th >
< th > Implemented< / th >
< th > LPCOMP wake< / th >
< th > VBUS wake< / th >
< / tr >
< / thead >
< tbody >
< tr >
< td > Seeed Studio XIAO nRF52840 (< code > xiao_nrf52< / code > )< / td >
< td > Yes< / td >
< td > Yes< / td >
< td > Yes< / td >
< / tr >
< tr >
< td > RAK4631 (< code > rak4631< / code > )< / td >
< td > Yes< / td >
< td > Yes< / td >
< td > Yes< / td >
< / tr >
< tr >
< td > Heltec T114 (< code > heltec_t114< / code > )< / td >
< td > Yes< / td >
< td > Yes< / td >
< td > Yes< / td >
< / tr >
< tr >
2026-04-19 01:35:26 +00:00
< td > GAT562 Mesh Watch13< / td >
< td > Yes< / td >
< td > Yes< / td >
< td > Yes< / td >
< / tr >
< tr >
2026-02-04 02:31:46 +00:00
< td > Promicro nRF52840< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > RAK WisMesh Tag< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > Heltec Mesh Solar< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > LilyGo T-Echo / T-Echo Lite< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > SenseCAP Solar< / td >
2026-03-12 07:13:33 +00:00
< td > Yes< / td >
< td > Yes< / td >
< td > Yes< / td >
2026-02-04 02:31:46 +00:00
< / tr >
< tr >
< td > WIO Tracker L1 / L1 E-Ink< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > WIO WM1110< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > Mesh Pocket< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > Nano G2 Ultra< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > ThinkNode M1/M3/M6< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > T1000-E< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > Ikoka Nano/Stick/Handheld (nRF)< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > Keepteen LT1< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< tr >
< td > Minewsemi ME25LS01< / td >
< td > No< / td >
< td > No< / td >
< td > No< / td >
< / tr >
< / tbody >
< / table >
< p > Notes:
- "Implemented" reflects Phase 1 (boot lockout + shutdown reason capture).
- User power-off on Heltec T114 does not enable LPCOMP wake.
- VBUS detection is used to skip boot lockout on external power, and VBUS wake is configured alongside LPCOMP when supported hardware exposes VBUS to the nRF52.< / p >
< h2 id = "technical-details" > Technical Details< / h2 >
< h3 id = "architecture" > Architecture< / h3 >
< p > The power management functionality is integrated into the < code > NRF52Board< / code > base class in < code > src/helpers/NRF52Board.cpp< / code > . Board variants provide hardware-specific configuration via a < code > PowerMgtConfig< / code > struct and override < code > initiateShutdown(uint8_t reason)< / code > to perform board-specific power-down work and conditionally enable voltage wake (LPCOMP + VBUS).< / p >
< h3 id = "early-boot-capture" > Early Boot Capture< / h3 >
< p > A static constructor with priority 101 in < code > NRF52Board.cpp< / code > captures the RESETREAS and GPREGRET2 registers before:
- SystemInit() (priority 102) - which clears RESETREAS
- Static C++ constructors (default priority 65535)< / p >
< p > This ensures we capture the true reset reason before any initialisation code runs.< / p >
< h3 id = "board-implementation" > Board Implementation< / h3 >
< p > To enable power management on a board variant:< / p >
< ol >
< li >
< p > < strong > Enable in platformio.ini< / strong > :
< code > ini
-D NRF52_POWER_MANAGEMENT< / code > < / p >
< / li >
< li >
< p > < strong > Define configuration in variant.h< / strong > :
< code > c
#define PWRMGT_VOLTAGE_BOOTLOCK 3300 // Won't boot below this voltage (mV)
#define PWRMGT_LPCOMP_AIN 7 // AIN channel for voltage sensing
#define PWRMGT_LPCOMP_REFSEL 2 // REFSEL (0-6=1/8..7/8, 7=ARef, 8-15=1/16..15/16)< / code > < / p >
< / li >
< li >
< p > < strong > Implement in board .cpp file< / strong > :
```cpp
#ifdef NRF52_POWER_MANAGEMENT
const PowerMgtConfig power_config = {
.lpcomp_ain_channel = PWRMGT_LPCOMP_AIN,
.lpcomp_refsel = PWRMGT_LPCOMP_REFSEL,
.voltage_bootlock = PWRMGT_VOLTAGE_BOOTLOCK
};< / p >
< / li >
< / ol >
< p > void MyBoard::initiateShutdown(uint8_t reason) {
// Board-specific shutdown preparation (e.g., disable peripherals)
bool enable_lpcomp = (reason == SHUTDOWN_REASON_LOW_VOLTAGE ||
reason == SHUTDOWN_REASON_BOOT_PROTECT);< / p >
< pre > < code > if (enable_lpcomp) {
configureVoltageWake(power_config.lpcomp_ain_channel, power_config.lpcomp_refsel);
}
enterSystemOff(reason);
< / code > < / pre >
< p > }
#endif< / p >
< p > void MyBoard::begin() {
NRF52Board::begin(); // or NRF52BoardDCDC::begin()
// ... board setup ...< / p >
< p > #ifdef NRF52_POWER_MANAGEMENT
checkBootVoltage(& power_config);
#endif
}
```< / p >
< p > For user-initiated shutdowns, < code > powerOff()< / code > remains board-specific. Power management only arms LPCOMP for automated shutdown reasons (boot protection/low voltage).< / p >
< ol >
< li > < strong > Declare override in board .h file< / strong > :
< code > cpp
#ifdef NRF52_POWER_MANAGEMENT
void initiateShutdown(uint8_t reason) override;
#endif< / code > < / li >
< / ol >
< h3 id = "voltage-wake-configuration" > Voltage Wake Configuration< / h3 >
< p > The LPCOMP (Low Power Comparator) is configured to:
- Monitor the specified AIN channel (0-7 corresponding to P0.02-P0.05, P0.28-P0.31)
- Compare against VDD fraction reference (REFSEL: 0-6=1/8..7/8, 7=ARef, 8-15=1/16..15/16)
- Detect UP events (voltage rising above threshold)
- Use 50mV hysteresis for noise immunity
- Wake the device from SYSTEMOFF when triggered< / p >
< p > VBUS wake is enabled via the POWER peripheral USBDETECTED event whenever < code > configureVoltageWake()< / code > is used. This requires USB VBUS to be routed to the nRF52 (typical on nRF52840 boards with native USB).< / p >
< p > < strong > LPCOMP Reference Selection (PWRMGT_LPCOMP_REFSEL)< / strong > :
| REFSEL | Fraction | VBAT @ 1M/1M divider (VDD=3.0-3.3) | VBAT @ 1.5M/1M divider (VDD=3.0-3.3) |
|--------|----------|------------------------------------|--------------------------------------|
| 0 | 1/8 | 0.75-0.82 V | 0.94-1.03 V |
| 1 | 2/8 | 1.50-1.65 V | 1.88-2.06 V |
| 2 | 3/8 | 2.25-2.47 V | 2.81-3.09 V |
| 3 | 4/8 | 3.00-3.30 V | 3.75-4.12 V |
| 4 | 5/8 | 3.75-4.12 V | 4.69-5.16 V |
| 5 | 6/8 | 4.50-4.95 V | 5.62-6.19 V |
| 6 | 7/8 | 5.25-5.77 V | 6.56-7.22 V |
| 7 | ARef | - | - |
| 8 | 1/16 | 0.38-0.41 V | 0.47-0.52 V |
| 9 | 3/16 | 1.12-1.24 V | 1.41-1.55 V |
| 10 | 5/16 | 1.88-2.06 V | 2.34-2.58 V |
| 11 | 7/16 | 2.62-2.89 V | 3.28-3.61 V |
| 12 | 9/16 | 3.38-3.71 V | 4.22-4.64 V |
| 13 | 11/16 | 4.12-4.54 V | 5.16-5.67 V |
| 14 | 13/16 | 4.88-5.36 V | 6.09-6.70 V |
| 15 | 15/16 | 5.62-6.19 V | 7.03-7.73 V |< / p >
< p > < strong > Important< / strong > : For boards with a voltage divider on the battery sense pin, LPCOMP measures the divided voltage. Use:
< code > VBAT_threshold ≈ (VDD * fraction) * divider_scale< / code > , where < code > divider_scale = (Rtop + Rbottom) / Rbottom< / code > (e.g., 2.0 for 1M/1M, 2.5 for 1.5M/1M, 3.0 for XIAO).< / p >
< h3 id = "softdevice-compatibility" > SoftDevice Compatibility< / h3 >
< p > The power management code checks whether SoftDevice is enabled and uses the appropriate API:
- When SD enabled: < code > sd_power_*< / code > functions
- When SD disabled: Direct register access (NRF_POWER-> *)< / p >
< p > This ensures compatibility regardless of BLE stack state.< / p >
< h2 id = "cli-commands" > CLI Commands< / h2 >
< p > Power management status can be queried via the CLI:< / p >
< table >
< thead >
< tr >
< th > Command< / th >
< th > Description< / th >
< / tr >
< / thead >
< tbody >
< tr >
< td > < code > get pwrmgt.support< / code > < / td >
< td > Returns "supported" or "unsupported"< / td >
< / tr >
< tr >
< td > < code > get pwrmgt.source< / code > < / td >
< td > Returns current power source - "battery" or "external" (5V/USB power)< / td >
< / tr >
< tr >
< td > < code > get pwrmgt.bootreason< / code > < / td >
< td > Returns reset and shutdown reason strings< / td >
< / tr >
< tr >
< td > < code > get pwrmgt.bootmv< / code > < / td >
< td > Returns boot voltage in millivolts< / td >
< / tr >
< / tbody >
< / table >
< p > On boards without power management enabled, all commands except < code > get pwrmgt.support< / code > return:< / p >
< pre > < code > ERROR: Power management not supported
< / code > < / pre >
< h2 id = "debug-output" > Debug Output< / h2 >
< p > When < code > MESH_DEBUG=1< / code > is enabled, the power management module outputs:< / p >
< pre > < code > DEBUG: PWRMGT: Reset = Wake from LPCOMP (0x20000); Shutdown = Low Voltage (0x4C)
DEBUG: PWRMGT: Boot voltage = 3450 mV (threshold = 3300 mV)
DEBUG: PWRMGT: LPCOMP wake configured (AIN7, ref=3/8 VDD)
< / code > < / pre >
< h2 id = "phase-2-planned" > Phase 2 (Planned)< / h2 >
< ul >
< li > Runtime voltage monitoring< / li >
< li > Voltage state machine (Normal -> Warning -> Critical -> Shutdown)< / li >
< li > Configurable thresholds< / li >
< li > Load shedding callbacks for power reduction< / li >
< li > Deep sleep integration< / li >
< li > Scheduled wake-up< / li >
< li > Extended sleep with periodic monitoring< / li >
< / ul >
< h2 id = "references" > References< / h2 >
< ul >
< li > < a href = "https://infocenter.nordicsemi.com/topic/ps_nrf52840/power.html" > nRF52840 Product Specification - POWER< / a > < / li >
< li > < a href = "https://infocenter.nordicsemi.com/topic/ps_nrf52840/lpcomp.html" > nRF52840 Product Specification - LPCOMP< / a > < / li >
< li > < a href = "https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.1.0/group__nrf__sdm__api.html" > SoftDevice S140 API - Power Management< / a > < / li >
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