Reading continuously RTC in STM32F4 ar 180MHz

[Jefferson Cunalata]

I have problems when I read continuously the RTC time in stm32f446 at 180MHz, after some readings, this gives me the same value. To find a solution, I implement a delay of 1 second to read the RTC and this solves the problem, however, I don't know what is the source of the issue. I am using HAL library for read the RTC.

[waclawek.jan]

> I read continuously the RTC time

How exactly?

Are you aware of the RTC_CR.BYPSHAD bit and that if it's cleared, you have to read RTC->DR after you've read RTC->TR? Read Reading the calendar chapter in RM.

JW

[Jefferson Cunalata]

Yes, I dont perform any change to RTC_CR.BYPSHAD bit so I suppose that this uses the deafult value which is cleared, however, I was looking to check this by using stm32ide with SFRs view tool, but the bit is not including here, however, the total register is showed and this effectivly is cleared. I attach the picture.

I am using the HAL library to get the time, so I assume it is correct. Here de code:

/**
  * @brief  Gets RTC current time.
  * @param  hrtc pointer to a RTC_HandleTypeDef structure that contains
  *                the configuration information for RTC.
  * @param  sTime Pointer to Time structure
  * @param  Format Specifies the format of the entered parameters.
  *          This parameter can be one of the following values:
  *            @arg RTC_FORMAT_BIN: Binary data format
  *            @arg RTC_FORMAT_BCD: BCD data format
  * @note  You can use SubSeconds and SecondFraction (sTime structure fields returned) to convert SubSeconds
  *        value in second fraction ratio with time unit following generic formula:
  *        Second fraction ratio * time_unit= [(SecondFraction-SubSeconds)/(SecondFraction+1)] * time_unit
  *        This conversion can be performed only if no shift operation is pending (ie. SHFP=0) when PREDIV_S >= SS
  * @note You must call HAL_RTC_GetDate() after HAL_RTC_GetTime() to unlock the values
  *        in the higher-order calendar shadow registers to ensure consistency between the time and date values.
  *        Reading RTC current time locks the values in calendar shadow registers until current date is read.
  * @retval HAL status
  */
HAL_StatusTypeDef HAL_RTC_GetTime(RTC_HandleTypeDef *hrtc, RTC_TimeTypeDef *sTime, uint32_t Format)
{
  uint32_t tmpreg = 0U;
 
  /* Check the parameters */
  assert_param(IS_RTC_FORMAT(Format));
 
  /* Get subseconds structure field from the corresponding register */
  sTime->SubSeconds = (uint32_t)(hrtc->Instance->SSR);
 
  /* Get SecondFraction structure field from the corresponding register field*/
  sTime->SecondFraction = (uint32_t)(hrtc->Instance->PRER & RTC_PRER_PREDIV_S);
 
  /* Get the TR register */
  tmpreg = (uint32_t)(hrtc->Instance->TR & RTC_TR_RESERVED_MASK);
 
  /* Fill the structure fields with the read parameters */
  sTime->Hours = (uint8_t)((tmpreg & (RTC_TR_HT | RTC_TR_HU)) >> 16U);
  sTime->Minutes = (uint8_t)((tmpreg & (RTC_TR_MNT | RTC_TR_MNU)) >> 8U);
  sTime->Seconds = (uint8_t)(tmpreg & (RTC_TR_ST | RTC_TR_SU));
  sTime->TimeFormat = (uint8_t)((tmpreg & (RTC_TR_PM)) >> 16U);
 
  /* Check the input parameters format */
  if(Format == RTC_FORMAT_BIN)
  {
    /* Convert the time structure parameters to Binary format */
    sTime->Hours = (uint8_t)RTC_Bcd2ToByte(sTime->Hours);
    sTime->Minutes = (uint8_t)RTC_Bcd2ToByte(sTime->Minutes);
    sTime->Seconds = (uint8_t)RTC_Bcd2ToByte(sTime->Seconds);
  }
 
  return HAL_OK;
}

[waclawek.jan · Accepted solution]

OK, so

- set the BYPSHD bit when setting up the RTC, or

- always read date after reading time,

or do both.

JW

[Jefferson Cunalata]

That is, I was just reading time without read date, now for each time reading operation I make read date operation and this solve the problen.

Thank you very much.