RTC_ERR_ALARM_MISSED embedded runtime_error ai_generated true

RTC: Alarm interrupt missed, VBAT low flag set

ID: embedded/rtc-alarm-missed-due-to-battery-loss

Also available as: JSON · Markdown · 中文
90%Fix Rate
82%Confidence
1Evidence
2023-11-20First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
STM32L4 RTC driver v1.3.0 active — — —
HAL RTC v1.2.5 active — — —

Root Cause

The backup battery (VBAT) voltage dropped below the threshold, causing the RTC registers to reset and the alarm to be missed.

generic

中文

备份电池电压降至阈值以下，导致RTC寄存器复位，闹钟丢失。

Official Documentation

https://www.st.com/resource/en/application_note/an4759-rtc-usage-with-stm32l4-series-stmicroelectronics.pdf

Workarounds

  1. 95% success Replace the backup battery and reinitialize the RTC with the correct time and alarm: `rtc_init(); rtc_set_time(&correct_time); rtc_set_alarm(&alarm_time);` 
    Replace the backup battery and reinitialize the RTC with the correct time and alarm: `rtc_init(); rtc_set_time(&correct_time); rtc_set_alarm(&alarm_time);`
  2. 80% success Add a VBAT monitoring routine to warn the user before the battery is critically low: `if (rtc_check_vbat_low()) { log_warning('VBAT low, replace battery'); }` 
    Add a VBAT monitoring routine to warn the user before the battery is critically low: `if (rtc_check_vbat_low()) { log_warning('VBAT low, replace battery'); }`

中文步骤

  1. Replace the backup battery and reinitialize the RTC with the correct time and alarm: `rtc_init(); rtc_set_time(&correct_time); rtc_set_alarm(&alarm_time);`
  2. Add a VBAT monitoring routine to warn the user before the battery is critically low: `if (rtc_check_vbat_low()) { log_warning('VBAT low, replace battery'); }`

Dead Ends

Common approaches that don't work:

  1. 85% fail

    If VBAT is low, the RTC registers will reset again after the next power loss, and the alarm will be missed repeatedly.

  2. 90% fail

    Disabling the flag only hides the symptom; the RTC data integrity is still compromised and alarms will fail silently.