Power

Overview

The modes trade wakeup latency and retained state against current draw. Picking one is mostly about what you need alive while asleep and how you’ll wake:

• Sleep — CPU halted, peripherals and clocks running. Wakes on any interrupt, ~instantly. The everyday idle.
• Stop — clocks halted, RAM retained. Wakes from EXTI or the RTC; the clock tree is rebuilt on wake.
• Standby — almost everything off; RAM is lost and wakeup is a full reset. Lowest draw.

Sleep, stop & standby

The Core calls bundle entry, wakeup configuration, and (for stop) clock recovery into one call. core_sleep returns on the next interrupt; core_stop_for wakes itself after N seconds:

#include "core.h"

core_sleep();                 // idle until any interrupt

core_stop_for(3);             // Stop for 3 s (RTC), then resume with clocks restored

core_standby_for(60);         // Standby 60 s — wakes via full reset (never returns)

Wakeup & the RTC

Beyond a timed interval, you can wake on a pin edge, and the RTC gives you a wall clock with periodic wakeups and a calendar alarm:

// Wake from Stop on a falling edge on pad 8:
core_stop_until_on_change(8, EDGE_FALLING);

// RTC wall clock + alarm:
core_rtc_init();
core_rtc_set_time(12, 0, 0);
core_rtc_set_alarm(0xFF, 0xFF, 0);   // 0xFF = wildcard → fire every minute at :00
if (core_rtc_alarm_fired()) { ... }

Check core_woke_from_standby() first thing in main() to branch on a Standby return, then core_clear_standby_flag() to acknowledge it.

Backup registers

Backup registers are 32-bit slots that survive reset and Standby (and power loss, with VBAT). Use them for crash counters, boot flags, or carrying state across a Standby cycle:

core_backup_write(0, 0x12345678);
uint32_t saved = core_backup_read(0);   // persists across reset / Standby

Cross-architecture support

Sleep is verified across the family; Stop and Standby are further along on some Cores than others (Stop is hardware-verified on L4 and H5, compile-only elsewhere). RTC and backup registers are broadly available:

See the implementation status for the full matrix.

API reference

Power modes

void core_sleep(void);

void core_stop_for(uint32_t seconds);

int core_woke_from_standby(void);

void core_stop_until_on_change(uint8_t pad, uint32_t edge);

void core_standby_for(void);

void core_standby_until_on_change(uint8_t pad, uint32_t edge);

void core_stop(void);

void core_standby(void);

void core_clear_standby_flag(void);

void core_watchdog_start_seconds(uint32_t seconds);

RTC

void core_rtc_init(void);

void core_rtc_set_time(uint8_t h, uint8_t m, uint8_t s);

void core_rtc_set_date(uint8_t y, uint8_t mo, uint8_t d, uint8_t wd);

void core_rtc_wakeup(uint32_t seconds);

void core_rtc_wakeup_stop(void);

void core_rtc_set_alarm(uint8_t hours, uint8_t minutes, uint8_t seconds);

void core_rtc_clear_alarm(void);

int core_rtc_alarm_fired(void);

void core_rtc_get_time(uint8_t * h, uint8_t * m, uint8_t * s);

void core_rtc_get_date(uint8_t * y, uint8_t * mo, uint8_t * d, uint8_t * wd);

Backup registers

uint32_t core_backup_read(uint8_t index);

void core_backup_write(uint8_t index, uint32_t value);

void _core_backup_ensure_clk(void);