我这套读取顺序就是 ST HAL 库函数内部的执行逻辑： HAL_RTC_GetTime() 会读取 SSR 亚秒寄存器 + 时间寄存器； HAL_RTC_GetDate() 读取日期寄存器。

以 5Hz 频率读取 RTC持续测试，每隔数小时就会出现一次读数错误；因此我写了一段代码，出错时重新完整读取一遍所有寄存器。能暂时妥协一下 int getrtc (struct tm * mytime)

{

RTC_TimeTypeDef sTime = {0};

RTC_DateTypeDef sDate = {0};

int rtcret1=0;

int rtcret2=0;

RTC_Lock();

// Implement RTC errata sheet (SSR needs reading before and after date/time and compared, until same)

uint32_t last_subsec;

volatile uint32_t errorcnt=0; // for doing a breakpoint

do

{

last_subsec = (uint32_t)(hrtc.Instance->SSR);

// Always read both, even if 1st returns an error

rtcret1 = HAL_RTC_GetTime(&hrtc, &sTime, RTC_FORMAT_BIN);

rtcret2 = HAL_RTC_GetDate(&hrtc, &sDate, RTC_FORMAT_BIN);

errorcnt++;

}

while (last_subsec != sTime.SubSeconds);

RTC_Unlock();

if ( (rtcret1!=0) || (rtcret2!=0))

return 2;

// Convert the 32F4 RTC API to the K&R standard C clock structure "tm"

// Comments in setrtc above

// No error checking - would be meaningless

mytime->tm_year = sDate.Year+100;

mytime->tm_mon = sDate.Month-1;

mytime->tm_mday = sDate.Date;

mytime->tm_wday = sDate.WeekDay; // assume the RTC maintained the day of week correctly

if (sDate.WeekDay==7) mytime->tm_wday = 0;

mytime->tm_hour = sTime.Hours;

mytime->tm_min = sTime.Minutes;

mytime->tm_sec = sTime.Seconds;

// Load subseconds into a global variable, as microseconds

// There were problems with this when using the SHIFTR method to advance the RTC...

g_SubSeconds = ((RTC_SYNC_PREDIV-sTime.SubSeconds)*1000000L)/(RTC_SYNC_PREDIV+1);

// Calculate day of year from the date, because that doesn't come from the RTC.

mytime->tm_yday = day_of_year(mytime->tm_mday, mytime->tm_mon, mytime->tm_year);

// Return -1 for daylight saving, as per K&R

mytime->tm_isdst = -1;

return 0;

}

手册中关于RTC 读取有一些说明，包括读取方式，读取时 总线速度。不同速度下的方式也有区别。可以对照一下。