# RTC: LSE振荡器未就绪，切换到LSI备份时钟

- **ID:** `embedded/rtc-oscillator-failure`
- **领域:** embedded
- **类别:** hardware_error
- **验证级别:** ai_generated
- **修复率:** 80%

## 根因

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。

## 版本兼容性

| 版本 | 状态 | 引入 | 弃用 |
|------|------|------|------|
| STM32Cube_FW_H7_V1.11.0 | active | — | — |
| STM32Cube_FW_F4_V1.27.1 | active | — | — |
| GCC ARM Embedded 12.2.Rel1 | active | — | — |

## 解决方案

1. ```
   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.
   ```
2. ```
   Use an external 32.768 kHz square wave oscillator module (e.g., SiTime SiT1532) in bypass mode to bypass crystal issues.
   ```

## 无效尝试

- **** — The MCU RTC peripheral is designed for 32.768 kHz; a higher frequency won't oscillate correctly. (85% 失败率)
- **** — Overdriving can damage the crystal or cause spurious oscillations; proper load capacitance matching is required. (70% 失败率)
- **** — LSI is less accurate (typically ±5% vs ±20 ppm for LSE) and may cause RTC drift in time-sensitive applications. (90% 失败率)