arch/arm/src/stm32/stm32_rtcc.c

/****************************************************************************
 * arch/arm/src/stm32/stm32_rtcc.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <stdbool.h>
#include <time.h>
#include <errno.h>
#include <debug.h>

#include <nuttx/arch.h>
#include <nuttx/irq.h>
#include <nuttx/clock.h>

#include <arch/board/board.h>

#include "arm_internal.h"
#include "stm32_rcc.h"
#include "stm32_pwr.h"
#include "stm32_exti.h"
#include "stm32_rtc.h"

#ifdef CONFIG_STM32_RTC

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/* Configuration ************************************************************/

/* This RTC implementation supports only date/time RTC hardware */

#ifndef CONFIG_RTC_DATETIME
#  error "CONFIG_RTC_DATETIME must be set to use this driver"
#endif

#ifdef CONFIG_RTC_HIRES
#  error "CONFIG_RTC_HIRES must NOT be set with this driver"
#endif

#ifndef CONFIG_STM32_PWR
#  error "CONFIG_STM32_PWR must selected to use this driver"
#endif

/* Constants ****************************************************************/

#define SYNCHRO_TIMEOUT  (0x00020000)
#define INITMODE_TIMEOUT (0x00010000)

/****************************************************************************
 * Private Data
 ****************************************************************************/

/* Callback to use when the alarm expires */

#ifdef CONFIG_RTC_ALARM
static alarmcb_t g_alarmcb;
#endif

/****************************************************************************
 * Public Data
 ****************************************************************************/

/* g_rtc_enabled is set true after the RTC has successfully initialized */

volatile bool g_rtc_enabled = false;

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: rtc_dumpregs
 ****************************************************************************/

#ifdef CONFIG_DEBUG_RTC_INFO
static void rtc_dumpregs(const char *msg)
{
  rtcinfo("%s:\n", msg);
  rtcinfo("      TR: %08x\n", getreg32(STM32_RTC_TR));
  rtcinfo("      DR: %08x\n", getreg32(STM32_RTC_DR));
  rtcinfo("      CR: %08x\n", getreg32(STM32_RTC_CR));
  rtcinfo("     ISR: %08x\n", getreg32(STM32_RTC_ISR));
  rtcinfo("    PRER: %08x\n", getreg32(STM32_RTC_PRER));
  rtcinfo("    WUTR: %08x\n", getreg32(STM32_RTC_WUTR));
#ifndef CONFIG_STM32_STM32F30XX
  rtcinfo("  CALIBR: %08x\n", getreg32(STM32_RTC_CALIBR));
#endif
  rtcinfo("  ALRMAR: %08x\n", getreg32(STM32_RTC_ALRMAR));
  rtcinfo("  ALRMBR: %08x\n", getreg32(STM32_RTC_ALRMBR));
  rtcinfo("  SHIFTR: %08x\n", getreg32(STM32_RTC_SHIFTR));
  rtcinfo("    TSTR: %08x\n", getreg32(STM32_RTC_TSTR));
  rtcinfo("    TSDR: %08x\n", getreg32(STM32_RTC_TSDR));
  rtcinfo("   TSSSR: %08x\n", getreg32(STM32_RTC_TSSSR));
  rtcinfo("    CALR: %08x\n", getreg32(STM32_RTC_CALR));
  rtcinfo("   TAFCR: %08x\n", getreg32(STM32_RTC_TAFCR));
  rtcinfo("ALRMASSR: %08x\n", getreg32(STM32_RTC_ALRMASSR));
  rtcinfo("ALRMBSSR: %08x\n", getreg32(STM32_RTC_ALRMBSSR));
  rtcinfo("MAGICREG: %08x\n", getreg32(RTC_MAGIC_REG));
}
#else
#  define rtc_dumpregs(msg)
#endif

/****************************************************************************
 * Name: rtc_dumptime
 ****************************************************************************/

#ifdef CONFIG_DEBUG_RTC_INFO
static void rtc_dumptime(struct tm *tp, const char *msg)
{
  rtcinfo("%s:\n", msg);
  rtcinfo("  tm_sec: %08x\n", tp->tm_sec);
  rtcinfo("  tm_min: %08x\n", tp->tm_min);
  rtcinfo(" tm_hour: %08x\n", tp->tm_hour);
  rtcinfo(" tm_mday: %08x\n", tp->tm_mday);
  rtcinfo("  tm_mon: %08x\n", tp->tm_mon);
  rtcinfo(" tm_year: %08x\n", tp->tm_year);
}
#else
#  define rtc_dumptime(tp, msg)
#endif

/****************************************************************************
 * Name: rtc_wprunlock
 *
 * Description:
 *    Disable RTC write protection
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

static void rtc_wprunlock(void)
{
  /* Enable write access to the backup domain (RTC registers, RTC backup data
   * registers and backup SRAM).
   */

  stm32_pwr_enablebkp(true);

  /* The following steps are required to unlock the write protection on all
   * the RTC registers (except for RTC_ISR[13:8], RTC_TAFCR, and RTC_BKPxR).
   *
   * 1. Write 0xCA into the RTC_WPR register.
   * 2. Write 0x53 into the RTC_WPR register.
   *
   * Writing a wrong key re-activates the write protection.
   */

  putreg32(0xca, STM32_RTC_WPR);
  putreg32(0x53, STM32_RTC_WPR);
}

/****************************************************************************
 * Name: rtc_wprlock
 *
 * Description:
 *    Enable RTC write protection
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

static inline void rtc_wprlock(void)
{
  /* Writing any wrong key re-activates the write protection. */

  putreg32(0xff, STM32_RTC_WPR);

  /* Disable write access to the backup domain (RTC registers, RTC backup
   * data registers and backup SRAM).
   */

  stm32_pwr_enablebkp(false);
}

/****************************************************************************
 * Name: rtc_synchwait
 *
 * Description:
 *   Waits until the RTC Time and Date registers (RTC_TR and RTC_DR) are
 *   synchronized with RTC APB clock.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

static int rtc_synchwait(void)
{
  volatile uint32_t timeout;
  uint32_t regval;
  int ret;

  /* Disable the write protection for RTC registers */

  rtc_wprunlock();

  /* Clear Registers synchronization flag (RSF) */

  regval  = getreg32(STM32_RTC_ISR);
  regval &= ~RTC_ISR_RSF;
  putreg32(regval, STM32_RTC_ISR);

  /* Now wait the registers to become synchronised */

  ret = -ETIMEDOUT;
  for (timeout = 0; timeout < SYNCHRO_TIMEOUT; timeout++)
    {
      regval = getreg32(STM32_RTC_ISR);
      if ((regval & RTC_ISR_RSF) != 0)
        {
          /* Synchronized */

          ret = OK;
          break;
        }
    }

  /* Re-enable the write protection for RTC registers */

  rtc_wprlock();
  return ret;
}

/****************************************************************************
 * Name: rtc_enterinit
 *
 * Description:
 *   Enter RTC initialization mode.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

static int rtc_enterinit(void)
{
  volatile uint32_t timeout;
  uint32_t regval;
  int ret;

  /* Check if the Initialization mode is already set */

  regval = getreg32(STM32_RTC_ISR);

  ret = OK;
  if ((regval & RTC_ISR_INITF) == 0)
    {
      /* Set the Initialization mode */

      putreg32(RTC_ISR_INIT, STM32_RTC_ISR);

      /* Wait until the RTC is in the INIT state (or a timeout occurs) */

      ret = -ETIMEDOUT;
      for (timeout = 0; timeout < INITMODE_TIMEOUT; timeout++)
        {
          regval = getreg32(STM32_RTC_ISR);
          if ((regval & RTC_ISR_INITF) != 0)
            {
              ret = OK;
              break;
            }
        }
    }

  return ret;
}

/****************************************************************************
 * Name: rtc_exitinit
 *
 * Description:
 *   Exit RTC initialization mode.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

static void rtc_exitinit(void)
{
  uint32_t regval;

  regval = getreg32(STM32_RTC_ISR);
  regval &= ~(RTC_ISR_INIT);
  putreg32(regval, STM32_RTC_ISR);
}

/****************************************************************************
 * Name: rtc_bin2bcd
 *
 * Description:
 *   Converts a 2 digit binary to BCD format
 *
 * Input Parameters:
 *   value - The byte to be converted.
 *
 * Returned Value:
 *   The value in BCD representation
 *
 ****************************************************************************/

static uint32_t rtc_bin2bcd(int value)
{
  uint32_t msbcd = 0;

  while (value >= 10)
    {
      msbcd++;
      value -= 10;
    }

  return (msbcd << 4) | value;
}

/****************************************************************************
 * Name: rtc_bin2bcd
 *
 * Description:
 *   Convert from 2 digit BCD to binary.
 *
 * Input Parameters:
 *   value - The BCD value to be converted.
 *
 * Returned Value:
 *   The value in binary representation
 *
 ****************************************************************************/

static int rtc_bcd2bin(uint32_t value)
{
  uint32_t tens = (value >> 4) * 10;
  return (int)(tens + (value & 0x0f));
}

/****************************************************************************
 * Name: rtc_setup
 *
 * Description:
 *   Performs first time configuration of the RTC.  A special value written
 *   into back-up register 0 will prevent this function from being called on
 *   sub-sequent resets or power up.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

static int rtc_setup(void)
{
  uint32_t regval;
  int ret;

  /* Disable the write protection for RTC registers */

  rtc_wprunlock();

  /* Set Initialization mode */

  ret = rtc_enterinit();
  if (ret == OK)
    {
      /* Set the 24 hour format by clearing the FMT bit in the RTC
       * control register
       */

      regval = getreg32(STM32_RTC_CR);
      regval &= ~RTC_CR_FMT;
      putreg32(regval, STM32_RTC_CR);

      /* Configure RTC pre-scaler with the required values */

#ifdef CONFIG_STM32_RTC_HSECLOCK
      /* STMicro app note AN4759 suggests using 7999 and 124 to
       * get exactly 1MHz when using the RTC at 8MHz.
       */

      putreg32(((uint32_t)7999 << RTC_PRER_PREDIV_S_SHIFT) |
              ((uint32_t)124 << RTC_PRER_PREDIV_A_SHIFT),
              STM32_RTC_PRER);
#else
      /* Correct values for 32.768 KHz LSE clock and inaccurate LSI clock */

      putreg32(((uint32_t)0xff << RTC_PRER_PREDIV_S_SHIFT) |
              ((uint32_t)0x7f << RTC_PRER_PREDIV_A_SHIFT),
              STM32_RTC_PRER);
#endif

      /* Exit RTC initialization mode */

      rtc_exitinit();
    }

  /* Re-enable the write protection for RTC registers */

  rtc_wprlock();

  return ret;
}

/****************************************************************************
 * Name: rtc_resume
 *
 * Description:
 *   Called when the RTC was already initialized on a previous power cycle.
 *   This just brings the RTC back into full operation.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

static void rtc_resume(void)
{
#ifdef CONFIG_RTC_ALARM
  uint32_t regval;

  /* Clear the RTC alarm flags */

  regval  = getreg32(STM32_RTC_ISR);
  regval &= ~(RTC_ISR_ALRAF | RTC_ISR_ALRBF);
  putreg32(regval, STM32_RTC_ISR);

  /* Clear the EXTI Line 17 Pending bit (Connected internally to RTC Alarm) */

  putreg32((1 << 17), STM32_EXTI_PR);
#endif
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: up_rtc_initialize
 *
 * Description:
 *   Initialize the hardware RTC per the selected configuration.
 *   This function is called once during the OS initialization sequence
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

int up_rtc_initialize(void)
{
  uint32_t regval;
  uint32_t tr_bkp;
  uint32_t dr_bkp;
  int ret;
  int maxretry = 10;
  int nretry = 0;

  /* Clocking for the PWR block must be provided.  However, this is done
   * unconditionally in stm32f40xxx_rcc.c on power up.  This done
   * unconditionally because the PWR block is also needed to set the internal
   * voltage regulator for maximum performance.
   */

  rtc_dumpregs("On reset");

  /* Select the clock source */

  /* Save the token before losing it when resetting */

  regval = getreg32(RTC_MAGIC_REG);

  stm32_pwr_enablebkp(true);

  if (regval != RTC_MAGIC && regval != RTC_MAGIC_TIME_SET)
    {
      /* Some boards do not have the external 32khz oscillator installed,
       * for those boards we must fallback to the crummy internal RC clock
       * or the external high rate clock
       */

#ifdef CONFIG_STM32_RTC_HSECLOCK
      /* Use the HSE clock as the input to the RTC block */

      modifyreg32(STM32_RCC_BDCR, RCC_BDCR_RTCSEL_MASK, RCC_BDCR_RTCSEL_HSE);

#elif defined(CONFIG_STM32_RTC_LSICLOCK)
      /* Use the LSI clock as the input to the RTC block */

      modifyreg32(STM32_RCC_BDCR, RCC_BDCR_RTCSEL_MASK, RCC_BDCR_RTCSEL_LSI);

#elif defined(CONFIG_STM32_RTC_LSECLOCK)
      /* Use the LSE clock as the input to the RTC block */

      modifyreg32(STM32_RCC_BDCR, RCC_BDCR_RTCSEL_MASK, RCC_BDCR_RTCSEL_LSE);

#endif
      /* Enable the RTC Clock by setting the RTCEN bit in the RCC register */

      modifyreg32(STM32_RCC_BDCR, 0, RCC_BDCR_RTCEN);
    }
  else /* The RTC is already in use: check if the clock source is changed */
    {
#if defined(CONFIG_STM32_RTC_HSECLOCK) || defined(CONFIG_STM32_RTC_LSICLOCK) || \
    defined(CONFIG_STM32_RTC_LSECLOCK)

      uint32_t clksrc = getreg32(STM32_RCC_BDCR);

#if defined(CONFIG_STM32_RTC_HSECLOCK)
      if ((clksrc & RCC_BDCR_RTCSEL_MASK) != RCC_BDCR_RTCSEL_HSE)
#elif defined(CONFIG_STM32_RTC_LSICLOCK)
      if ((clksrc & RCC_BDCR_RTCSEL_MASK) != RCC_BDCR_RTCSEL_LSI)
#elif defined(CONFIG_STM32_RTC_LSECLOCK)
      if ((clksrc & RCC_BDCR_RTCSEL_MASK) != RCC_BDCR_RTCSEL_LSE)
#endif
#endif
        {
          tr_bkp = getreg32(STM32_RTC_TR);
          dr_bkp = getreg32(STM32_RTC_DR);
          modifyreg32(STM32_RCC_BDCR, 0, RCC_BDCR_BDRST);
          modifyreg32(STM32_RCC_BDCR, RCC_BDCR_BDRST, 0);

#if defined(CONFIG_STM32_RTC_HSECLOCK)
          /* Change to the new clock as the input to the RTC block */

          modifyreg32(STM32_RCC_BDCR,
                      RCC_BDCR_RTCSEL_MASK, RCC_BDCR_RTCSEL_HSE);

#elif defined(CONFIG_STM32_RTC_LSICLOCK)
          modifyreg32(STM32_RCC_BDCR,
                      RCC_BDCR_RTCSEL_MASK, RCC_BDCR_RTCSEL_LSI);

#elif defined(CONFIG_STM32_RTC_LSECLOCK)
          modifyreg32(STM32_RCC_BDCR,
                      RCC_BDCR_RTCSEL_MASK, RCC_BDCR_RTCSEL_LSE);
#endif

          putreg32(tr_bkp, STM32_RTC_TR);
          putreg32(dr_bkp, STM32_RTC_DR);

          /* Remember that the RTC is initialized */

          putreg32(RTC_MAGIC, RTC_MAGIC_REG);

          /* Enable the RTC Clock by setting the RTCEN bit in the RCC
           * register
           */

          modifyreg32(STM32_RCC_BDCR, 0, RCC_BDCR_RTCEN);
        }
    }

  stm32_pwr_enablebkp(false);

  /* Loop, attempting to initialize/resume the RTC.  This loop is necessary
   * because it seems that occasionally it takes longer to initialize the RTC
   * (the actual failure is in rtc_synchwait()).
   */

  do
    {
      /* Wait for the RTC Time and Date registers to be synchronized with RTC
       * APB clock.
       */

      ret = rtc_synchwait();

      /* Check that rtc_syncwait() returned successfully */

      switch (ret)
        {
          case OK:
            {
              rtcinfo("rtc_syncwait() okay\n");
              break;
            }

          default:
            {
              rtcerr("ERROR: rtc_syncwait() failed (%d)\n", ret);
              break;
            }
        }
    }
  while (ret != OK && ++nretry < maxretry);

  /* Check if the one-time initialization of the RTC has already been
   * performed. We can determine this by checking if the magic number
   * has been written to the back-up date register DR0.
   */

  if (regval != RTC_MAGIC && regval != RTC_MAGIC_TIME_SET)
    {
      rtcinfo("Do setup\n");

      /* Perform the one-time setup of the LSE clocking to the RTC */

      ret = rtc_setup();

      /* Enable write access to the backup domain (RTC registers, RTC
       * backup data registers and backup SRAM).
       */

      stm32_pwr_enablebkp(true);

      /* Remember that the RTC is initialized */

      putreg32(RTC_MAGIC, RTC_MAGIC_REG);

      /* Disable write access to the backup domain (RTC registers, RTC
       * backup data registers and backup SRAM).
       */

      stm32_pwr_enablebkp(false);
    }
  else
    {
      rtcinfo("Do resume\n");

      /* RTC already set-up, just resume normal operation */

      rtc_resume();
      rtc_dumpregs("Did resume");
    }

  if (ret != OK && nretry > 0)
    {
      rtcinfo("setup/resume ran %d times and failed with %d\n",
              nretry, ret);
      return -ETIMEDOUT;
    }

  /* Configure RTC interrupt to catch alarm interrupts. All RTC interrupts
   * are connected to the EXTI controller.  To enable the RTC Alarm
   * interrupt, the following sequence is required:
   *
   * 1. Configure and enable the EXTI Line 17 in interrupt mode and select
   *    the rising edge sensitivity.
   * 2. Configure and enable the RTC_Alarm IRQ channel in the NVIC.
   * 3. Configure the RTC to generate RTC alarms (Alarm A or Alarm B).
   */

  g_rtc_enabled = true;
  rtc_dumpregs("After Initialization");
  return OK;
}

/****************************************************************************
 * Name: stm32_rtc_irqinitialize
 *
 * Description:
 *   Initialize IRQs for RTC, not possible during up_rtc_initialize because
 *   up_irqinitialize is called later.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

int stm32_rtc_irqinitialize(void)
{
#ifdef CONFIG_RTC_ALARM
#  warning "Missing logic"
#endif

  return OK;
}

/****************************************************************************
 * Name: stm32_rtc_getdatetime_with_subseconds
 *
 * Description:
 *   Get the current date and time from the date/time RTC.  This interface
 *   is only supported by the date/time RTC hardware implementation.
 *   It is used to replace the system timer.  It is only used by the RTOS
 *   during initialization to set up the system time when CONFIG_RTC and
 *   CONFIG_RTC_DATETIME are selected (and CONFIG_RTC_HIRES is not).
 *
 *   NOTE: Some date/time RTC hardware is capability of sub-second accuracy.
 *    That sub-second accuracy is returned through 'nsec'.
 *
 * Input Parameters:
 *   tp - The location to return the high resolution time value.
 *   nsec - The location to return the subsecond time value.
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

#ifdef CONFIG_STM32_HAVE_RTC_SUBSECONDS
int stm32_rtc_getdatetime_with_subseconds(struct tm *tp, long *nsec)
#else
int up_rtc_getdatetime(struct tm *tp)
#endif
{
#ifdef CONFIG_STM32_HAVE_RTC_SUBSECONDS
  uint32_t ssr;
#endif
  uint32_t dr;
  uint32_t tr;
  uint32_t tmp;

  /* Sample the data time registers.  There is a race condition here... If
   * we sample the time just before midnight on December 31, the date could
   * be wrong because the day rolled over while were sampling. Thus loop for
   * checking overflow here is needed.  There is a race condition with
   * subseconds too. If we sample TR register just before second rolling
   * and subseconds are read at wrong second, we get wrong time.
   */

  do
    {
      dr  = getreg32(STM32_RTC_DR);
      tr  = getreg32(STM32_RTC_TR);
#ifdef CONFIG_STM32_HAVE_RTC_SUBSECONDS
      ssr = getreg32(STM32_RTC_SSR);
      tmp = getreg32(STM32_RTC_TR);
      if (tmp != tr)
        {
          continue;
        }
#endif

      tmp = getreg32(STM32_RTC_DR);
      if (tmp == dr)
        {
          break;
        }
    }
  while (1);

  rtc_dumpregs("Reading Time");

  /* Convert the RTC time to fields in struct tm format.  All of the STM32
   * ranges of values correspond between struct tm and the time register.
   */

  tmp = (tr & (RTC_TR_SU_MASK | RTC_TR_ST_MASK)) >> RTC_TR_SU_SHIFT;
  tp->tm_sec = rtc_bcd2bin(tmp);

  tmp = (tr & (RTC_TR_MNU_MASK | RTC_TR_MNT_MASK)) >> RTC_TR_MNU_SHIFT;
  tp->tm_min = rtc_bcd2bin(tmp);

  tmp = (tr & (RTC_TR_HU_MASK | RTC_TR_HT_MASK)) >> RTC_TR_HU_SHIFT;
  tp->tm_hour = rtc_bcd2bin(tmp);

  /* Now convert the RTC date to fields in struct tm format:
   * Days: 1-31 match in both cases.
   * Month: STM32 is 1-12, struct tm is 0-11.
   * Years: STM32 is 00-99, struct tm is years since 1900.
   * WeekDay: STM32 is 1 = Mon - 7 = Sun
   *
   * Issue:  I am not sure what the STM32 years mean.  Are these the
   * years 2000-2099?  I'll assume so.
   */

  tmp = (dr & (RTC_DR_DU_MASK | RTC_DR_DT_MASK)) >> RTC_DR_DU_SHIFT;
  tp->tm_mday = rtc_bcd2bin(tmp);

  tmp = (dr & (RTC_DR_MU_MASK | RTC_DR_MT)) >> RTC_DR_MU_SHIFT;
  tp->tm_mon = rtc_bcd2bin(tmp) - 1;

  tmp = (dr & (RTC_DR_YU_MASK | RTC_DR_YT_MASK)) >> RTC_DR_YU_SHIFT;
  tp->tm_year = rtc_bcd2bin(tmp) + 100;

  tmp = (dr & RTC_DR_WDU_MASK) >> RTC_DR_WDU_SHIFT;
  tp->tm_wday = tmp % 7;
  tp->tm_yday = tp->tm_mday - 1 +
                clock_daysbeforemonth(tp->tm_mon,
                                      clock_isleapyear(tp->tm_year + 1900));
  tp->tm_isdst = 0;

#ifdef CONFIG_STM32_HAVE_RTC_SUBSECONDS
  /* Return RTC sub-seconds if no configured and if a non-NULL value
   * of nsec has been provided to receive the sub-second value.
   */

  if (nsec)
    {
      uint32_t prediv_s;
      uint32_t usecs;

      prediv_s   = getreg32(STM32_RTC_PRER) & RTC_PRER_PREDIV_S_MASK;
      prediv_s >>= RTC_PRER_PREDIV_S_SHIFT;

      ssr &= RTC_SSR_MASK;

      /* Maximum prediv_s is 0x7fff, thus we can multiply by 100000 and
       * still fit 32-bit unsigned integer.
       */

      usecs = (((prediv_s - ssr) * 100000) / (prediv_s + 1)) * 10;
      *nsec = usecs * 1000;
    }
#endif /* CONFIG_STM32_HAVE_RTC_SUBSECONDS */

  rtc_dumptime(tp, "Returning");
  return OK;
}

/****************************************************************************
 * Name: up_rtc_getdatetime
 *
 * Description:
 *   Get the current date and time from the date/time RTC.  This interface
 *   is only supported by the date/time RTC hardware implementation.
 *   It is used to replace the system timer.  It is only used by the RTOS
 *   during initialization to set up the system time when CONFIG_RTC and
 *   CONFIG_RTC_DATETIME are selected (and CONFIG_RTC_HIRES is not).
 *
 *   NOTE: Some date/time RTC hardware is capability of sub-second accuracy.
 *   That sub-second accuracy is lost in this interface.  However, since the
 *   system time is reinitialized on each power-up/reset, there will be no
 *   timing inaccuracy in the long run.
 *
 * Input Parameters:
 *   tp - The location to return the high resolution time value.
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

#ifdef CONFIG_STM32_HAVE_RTC_SUBSECONDS
int up_rtc_getdatetime(struct tm *tp)
{
  return stm32_rtc_getdatetime_with_subseconds(tp, NULL);
}
#endif

/****************************************************************************
 * Name: up_rtc_getdatetime_with_subseconds
 *
 * Description:
 *   Get the current date and time from the date/time RTC.  This interface
 *   is only supported by the date/time RTC hardware implementation.
 *   It is used to replace the system timer.  It is only used by the RTOS
 *   during initialization to set up the system time when CONFIG_RTC and
 *   CONFIG_RTC_DATETIME are selected (and CONFIG_RTC_HIRES is not).
 *
 *   NOTE:
 *   This interface exposes sub-second accuracy capability of RTC hardware.
 *   This interface allow maintaining timing accuracy when system time needs
 *   constant resynchronization with RTC, for example on MCU with low-power
 *   state that stop system timer.
 *
 * Input Parameters:
 *   tp - The location to return the high resolution time value.
 *   nsec - The location to return the subsecond time value.
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

#ifdef CONFIG_ARCH_HAVE_RTC_SUBSECONDS
#  ifndef CONFIG_STM32_HAVE_RTC_SUBSECONDS
#    error "Invalid config, enable CONFIG_STM32_HAVE_RTC_SUBSECONDS."
#  endif
int up_rtc_getdatetime_with_subseconds(struct tm *tp, long *nsec)
{
  return stm32_rtc_getdatetime_with_subseconds(tp, nsec);
}
#endif

/****************************************************************************
 * Name: stm32_rtc_setdatetime
 *
 * Description:
 *   Set the RTC to the provided time. RTC implementations which provide
 *   up_rtc_getdatetime() (CONFIG_RTC_DATETIME is selected) should provide
 *   this function.
 *
 * Input Parameters:
 *   tp - the time to use
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

int stm32_rtc_setdatetime(const struct tm *tp)
{
  uint32_t tr;
  uint32_t dr;
  int ret;

  rtc_dumptime(tp, "Setting time");

  /* Then write the broken out values to the RTC */

  /* Convert the struct tm format to RTC time register fields.  All of the
   * STM32 All of the ranges of values correspond between struct tm and the
   * time register.
   */

  tr = (rtc_bin2bcd(tp->tm_sec)  << RTC_TR_SU_SHIFT) |
       (rtc_bin2bcd(tp->tm_min)  << RTC_TR_MNU_SHIFT) |
       (rtc_bin2bcd(tp->tm_hour) << RTC_TR_HU_SHIFT);
  tr &= ~RTC_TR_RESERVED_BITS;

  /* Now convert the fields in struct tm format to the RTC date register
   * fields:
   * Days: 1-31 match in both cases.
   * Month: STM32 is 1-12, struct tm is 0-11.
   * Years: STM32 is 00-99, struct tm is years since 1900.
   * WeekDay: STM32 is 1 = Mon - 7 = Sun
   * Issue:  I am not sure what the STM32 years mean.  Are these the
   * years 2000-2099?  I'll assume so.
   */

  dr = (rtc_bin2bcd(tp->tm_mday) << RTC_DR_DU_SHIFT) |
       ((rtc_bin2bcd(tp->tm_mon + 1))  << RTC_DR_MU_SHIFT) |
       ((tp->tm_wday == 0 ? 7 : (tp->tm_wday & 7))  << RTC_DR_WDU_SHIFT) |
       ((rtc_bin2bcd(tp->tm_year - 100)) << RTC_DR_YU_SHIFT);

  dr &= ~RTC_DR_RESERVED_BITS;

  /* Disable the write protection for RTC registers */

  rtc_wprunlock();

  /* Set Initialization mode */

  ret = rtc_enterinit();
  if (ret == OK)
    {
      /* Set the RTC TR and DR registers */

      putreg32(tr, STM32_RTC_TR);
      putreg32(dr, STM32_RTC_DR);

      /* Exit Initialization mode and wait for the RTC Time and Date
       * registers to be synchronized with RTC APB clock.
       */

      rtc_exitinit();
      ret = rtc_synchwait();
    }

  /* Remember that the RTC is initialized and had its time set. */

  if (getreg32(RTC_MAGIC_REG) != RTC_MAGIC_TIME_SET)
    {
      stm32_pwr_enablebkp(true);
      putreg32(RTC_MAGIC_TIME_SET, RTC_MAGIC_REG);
      stm32_pwr_enablebkp(false);
    }

  /* Re-enable the write protection for RTC registers */

  rtc_wprlock();
  rtc_dumpregs("New time setting");
  return ret;
}

/****************************************************************************
 * Name: up_rtc_settime
 *
 * Description:
 *   Set the RTC to the provided time.  All RTC implementations must be able
 *   to set their time based on a standard timespec.
 *
 * Input Parameters:
 *   tp - the time to use
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

int up_rtc_settime(const struct timespec *tp)
{
  struct tm newtime;

  /* Break out the time values
   * (not that the time is set only to units of seconds)
   */

  gmtime_r(&tp->tv_sec, &newtime);
  return stm32_rtc_setdatetime(&newtime);
}

/****************************************************************************
 * Name: stm32_rtc_setalarm
 *
 * Description:
 *   Set up an alarm.
 *   Up to two alarms can be supported (ALARM A and ALARM B).
 *
 * Input Parameters:
 *   tp - the time to set the alarm
 *   callback - the function to call when the alarm expires.
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno on failure
 *
 ****************************************************************************/

#ifdef CONFIG_RTC_ALARM
int stm32_rtc_setalarm(const struct timespec *tp, alarmcb_t callback)
{
  int ret = -EBUSY;

  /* Is there already something waiting on the ALARM? */

  if (g_alarmcb == NULL)
    {
      /* No.. Save the callback function pointer */

      g_alarmcb = callback;

      /* Break out the time values */

#warning "Missing logic"

      /* The set the alarm */

#warning "Missing logic"

      ret = OK;
    }

  return ret;
}
#endif

#endif /* CONFIG_STM32_RTC */