{
  "id": "embedded/rtc-oscillator-failure",
  "signature": "RTC: LSE oscillator not ready, switching to LSI backup clock",
  "signature_zh": "RTC: LSE振荡器未就绪，切换到LSI备份时钟",
  "regex": "RTC: LSE oscillator not ready, switching to LSI backup clock",
  "domain": "embedded",
  "category": "hardware_error",
  "subcategory": null,
  "root_cause": "Low-speed external (LSE) crystal oscillator failed to start or stabilize, usually due to incorrect load capacitors, crystal damage, or PCB parasitics.",
  "root_cause_type": "generic",
  "root_cause_zh": "低速外部晶振未能启动或稳定，通常由于负载电容错误、晶振损坏或PCB寄生效应引起。",
  "versions": [
    {
      "version": "STM32Cube_FW_H7_V1.11.0",
      "introduced": null,
      "deprecated": null,
      "removed": null,
      "behavior_change": null,
      "status": "active"
    },
    {
      "version": "STM32Cube_FW_F4_V1.27.1",
      "introduced": null,
      "deprecated": null,
      "removed": null,
      "behavior_change": null,
      "status": "active"
    },
    {
      "version": "GCC ARM Embedded 12.2.Rel1",
      "introduced": null,
      "deprecated": null,
      "removed": null,
      "behavior_change": null,
      "status": "active"
    }
  ],
  "os_specific": {},
  "dead_ends": [
    {
      "action": "",
      "why_fails": "The MCU RTC peripheral is designed for 32.768 kHz; a higher frequency won't oscillate correctly.",
      "fail_rate": 0.85,
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "why_fails": "Overdriving can damage the crystal or cause spurious oscillations; proper load capacitance matching is required.",
      "fail_rate": 0.7,
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "why_fails": "LSI is less accurate (typically ±5% vs ±20 ppm for LSE) and may cause RTC drift in time-sensitive applications.",
      "fail_rate": 0.9,
      "condition": "",
      "sources": []
    }
  ],
  "workarounds": [
    {
      "action": "Verify LSE load capacitors: for a 12.5 pF crystal, use two 22 pF caps in series (effective 11 pF). Adjust via RCC_BDCR register in firmware if needed.",
      "success_rate": 0.75,
      "how": "Verify LSE load capacitors: for a 12.5 pF crystal, use two 22 pF caps in series (effective 11 pF). Adjust via RCC_BDCR register in firmware if needed.",
      "condition": "",
      "sources": []
    },
    {
      "action": "Use an external 32.768 kHz square wave oscillator module (e.g., SiTime SiT1532) in bypass mode to bypass crystal issues.",
      "success_rate": 0.95,
      "how": "Use an external 32.768 kHz square wave oscillator module (e.g., SiTime SiT1532) in bypass mode to bypass crystal issues.",
      "condition": "",
      "sources": []
    }
  ],
  "workarounds_zh": [
    "Verify LSE load capacitors: for a 12.5 pF crystal, use two 22 pF caps in series (effective 11 pF). Adjust via RCC_BDCR register in firmware if needed.",
    "Use an external 32.768 kHz square wave oscillator module (e.g., SiTime SiT1532) in bypass mode to bypass crystal issues."
  ],
  "transition_graph": {
    "leads_to": [],
    "preceded_by": [],
    "frequently_confused_with": []
  },
  "official_doc_url": "https://www.st.com/resource/en/application_note/dm00231744-oscillator-design-guide-for-stm32-mcus-and-mpus-stmicroelectronics.pdf",
  "official_doc_section": null,
  "error_code": null,
  "verification_tier": "ai_generated",
  "confidence": 0.85,
  "fix_success_rate": 0.8,
  "resolvable": "partial",
  "first_seen": "2024-02-15",
  "last_confirmed": "2024-06-01",
  "last_updated": "2024-06-01",
  "evidence_count": 1,
  "tags": [],
  "locale": "en",
  "aliases": []
}