---
tags: [entity]
type: entity
topic: stm32-lower
note: 19
created: 2026-07-16
updated: 2026-07-16
---

# Note 19: BKP/RTC (lower/stm32/21~26)

## Projects

| # | Directory | Topic | Library |
|---|---|---|---|
| 21 | `21_bkp_test_register` | BKP backup registers | Register |
| 22 | `22_bkp_test_hal` | BKP backup registers | HAL |
| 23 | `23_rtc_alarm_standby_register` | RTC alarm + standby wake | Register |
| 24 | `24_rtc_alarm_standby_hal` | RTC alarm + standby wake | HAL |
| 25 | `25_rtc_calendar_register` | RTC calendar | Register |
| 26 | `26_rtc_calendar_hal` | RTC calendar | HAL |

## Code Accuracy Audit

### Path Audit

| Claimed Path | Actual Path | Status |
|---|---|---|
| `stm32/21_bkp_test_register/Hardware/BKP/bkp.c` | `21_bkp_test_register/Hardware/BKP/bkp.c` | ✅ Correct |
| `stm32/25_rtc_calendar_register/Hardware/RTC/rtc.c` | `25_rtc_calendar_register/Hardware/RTC/rtc.c` | ✅ Correct |
| `stm32/25_rtc_calendar_register/Hardware/RTC/rtc.h` | `25_rtc_calendar_register/Hardware/RTC/rtc.h` | ✅ Correct |
| `stm32/25_rtc_calendar_register/User/main.c` | `25_rtc_calendar_register/User/main.c` | ✅ Correct |
| `stm32/23_rtc_alarm_standby_register/User/main.c` | `23_rtc_alarm_standby_register/User/main.c` | ✅ Correct |

### BKP Code (bkp.c)

| Claimed by Note | Actual Code | Match? |
|---|---|---|
| `RCC->APB1ENR |= RCC_APB1ENR_PWREN` | Present | ✅ Match |
| `PWR->CR |= PWR_CR_DBP` | Present | ✅ Match |
| `RCC->APB1ENR |= RCC_APB1ENR_BKPEN` | Present | ✅ Match |
| `bkp.h` has `#include "stm32f10x.h"`, `BKP_Init(void)` | Present | ✅ Match |

### RTC Init (25_rtc_calendar_register/Hardware/RTC/rtc.c)

| Claimed by Note | Actual Code (lines) | Match? |
|---|---|---|
| `RCC->APB1ENR |= RCC_APB1ENR_PWREN` | Line 15 | ✅ Match |
| `PWR->CR |= PWR_CR_DBP` | Line 18 | ✅ Match |
| `RCC->BDCR |= RCC_BDCR_RTCEN` | Line 28 | ✅ Match |
| `RCC->BDCR |= RCC_BDCR_LSEON` | Line 31 | ✅ Match |
| `while (!(RCC->BDCR & RCC_BDCR_LSERDY))` | Lines 32-34 | ✅ Match |
| `RCC->BDCR &= ~RCC_BDCR_RTCSEL; RCC->BDCR |= RCC_BDCR_RTCSEL_0` | Lines 37-38 | ✅ Match |
| Wait `RTC_CRL_RTOFF` | Lines 42-44 | ✅ Match |
| `RTC->CRL |= RTC_CRL_CNF` | Line 47 | ✅ Match |
| `RTC->PRLH = 0; RTC->PRLL = 0x7fff` | Lines 50-51 | ✅ Match |
| `RTC->CRL &= ~RTC_CRL_CNF` | Line 54 | ✅ Match |

### RTC_SetAlarm

| Claimed by Note | Actual Code | Match? |
|---|---|---|
| `RTC->CRL &= ~RTC_CRL_ALRF` | Line 66 | ✅ Match |
| Wait RTOFF | Line 69 | ✅ Match |
| `RTC->CRL |= RTC_CRL_CNF` | Line 74 | ✅ Match |
| `RTC->CNTH = 0; RTC->CNTL = 0` | Lines 78-79 | ✅ Match |
| `s -= 1; RTC->ALRH = (s >> 16) & 0xffff; RTC->ALRL = (s >> 0) & 0xffff` | Lines 82-84 | ✅ Match |
| `RTC->CRL &= ~RTC_CRL_CNF` | Line 87 | ✅ Match |

### RTC_SetTimestamp

| Claimed by Note | Actual Code | Match? |
|---|---|---|
| Wait RTOFF, CNF=1, set CNTH/CNTL, CNF=0, wait RTOFF | Lines 99-116 | ✅ Match |

### RTC_GetDateTime

| Claimed by Note | Actual Code | Match? |
|---|---|---|
| `while (!(RTC->CRL & RTC_CRL_RSF))` | Line 123 | ✅ Match |
| `uint32_t second = RTC->CNTH << 16 | RTC->CNTL` | Line 127 | ✅ Match |
| `struct tm* ptm = localtime(&second)` | Line 130 | ✅ Match |
| `dateTime->year = ptm->tm_year + 1900` etc. | Lines 133-138 | ✅ Match |

### DateTime struct (rtc.h)

| Claimed by Note | Actual Code | Match? |
|---|---|---|
| `typedef struct { uint16_t year; uint8_t month; ... } DateTime;` | Present | ✅ Match |
| Function prototypes: `RTC_Init`, `RTC_SetAlarm`, `RTC_SetTimestamp`, `RTC_GetDateTime` | Present | ✅ Match |

### RTC Alarm + Standby (23_rtc_alarm_standby_register)

Note claims loop: `RTC_SetAlarm(5); enter_standby_mode();` with PA0 wakeup → matches actual code.

### HAL RTC Calendar

Note's HAL code (`RTC_TimeTypeDef`, `RTC_DateTypeDef`, `HAL_RTC_SetTime`, `HAL_RTC_GetTime`) matches project 26.

### BKP Store Date (HAL)

Note's `read_stored_date` / `write_stored_date` functions using `HAL_RTCEx_BKUPRead/Write` — these exist in project 22's code.

## Summary

**Overall Accuracy**: Excellent (99%+)

**Issues Found**: None significant. RTC register operations, HAL API usage, BKP operations all match actual source files exactly. This is the most technically accurate section.