/** @file
  Simple PC RTC

  Copyright (c) 2007, Intel Corporation. All rights reserved.<BR>
  Portions copyright (c) 2008 - 2009, Apple Inc. All rights reserved.<BR>
  Copyright (c) 2014, ARM Ltd. All rights reserved.

  This program and the accompanying materials
  are licensed and made available under the terms and conditions of the BSD License
  which accompanies this distribution.  The full text of the license may be found at
  http://opensource.org/licenses/bsd-license.php

  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.


**/



typedef struct {
  EFI_LOCK  RtcLock;
  UINT16    SavedTimeZone;
  UINT8     Daylight;
} PC_RTC_GLOBALS;

#define PCAT_RTC_ADDRESS_REGISTER 0x70
#define PCAT_RTC_DATA_REGISTER    0x71

//
// Dallas DS12C887 Real Time Clock
//
#define RTC_ADDRESS_SECONDS           0   // R/W  Range 0..59
#define RTC_ADDRESS_SECONDS_ALARM     1   // R/W  Range 0..59
#define RTC_ADDRESS_MINUTES           2   // R/W  Range 0..59
#define RTC_ADDRESS_MINUTES_ALARM     3   // R/W  Range 0..59
#define RTC_ADDRESS_HOURS             4   // R/W  Range 1..12 or 0..23 Bit 7 is AM/PM
#define RTC_ADDRESS_HOURS_ALARM       5   // R/W  Range 1..12 or 0..23 Bit 7 is AM/PM
#define RTC_ADDRESS_DAY_OF_THE_WEEK   6   // R/W  Range 1..7
#define RTC_ADDRESS_DAY_OF_THE_MONTH  7   // R/W  Range 1..31
#define RTC_ADDRESS_MONTH             8   // R/W  Range 1..12
#define RTC_ADDRESS_YEAR              9   // R/W  Range 0..99
#define RTC_ADDRESS_REGISTER_A        10  // R/W[0..6]  R0[7]
#define RTC_ADDRESS_REGISTER_B        11  // R/W
#define RTC_ADDRESS_REGISTER_C        12  // RO
#define RTC_ADDRESS_REGISTER_D        13  // RO
#define RTC_ADDRESS_CENTURY           50  // R/W  Range 19..20 Bit 8 is R/W
//
// Date and time initial values.
// They are used if the RTC values are invalid during driver initialization
//
#define RTC_INIT_SECOND 0
#define RTC_INIT_MINUTE 0
#define RTC_INIT_HOUR   0
#define RTC_INIT_DAY    1
#define RTC_INIT_MONTH  1
#define RTC_INIT_YEAR   2001

//
// Register initial values
//
#define RTC_INIT_REGISTER_A 0x26
#define RTC_INIT_REGISTER_B 0x02
#define RTC_INIT_REGISTER_D 0x0

#pragma pack(1)
//
// Register A
//
typedef struct {
  UINT8 RS : 4;   // Rate Selection Bits
  UINT8 DV : 3;   // Divisor
  UINT8 UIP : 1;  // Update in progress
} RTC_REGISTER_A_BITS;

typedef union {
  RTC_REGISTER_A_BITS Bits;
  UINT8               Data;
} RTC_REGISTER_A;

//
// Register B
//
typedef struct {
  UINT8 DSE : 1;  // 0 - Daylight saving disabled  1 - Daylight savings enabled
  UINT8 MIL : 1;  // 0 - 12 hour mode              1 - 24 hour mode
  UINT8 DM : 1;   // 0 - BCD Format                1 - Binary Format
  UINT8 SQWE : 1; // 0 - Disable SQWE output       1 - Enable SQWE output
  UINT8 UIE : 1;  // 0 - Update INT disabled       1 - Update INT enabled
  UINT8 AIE : 1;  // 0 - Alarm INT disabled        1 - Alarm INT Enabled
  UINT8 PIE : 1;  // 0 - Periodic INT disabled     1 - Periodic INT Enabled
  UINT8 SET : 1;  // 0 - Normal operation.         1 - Updates inhibited
} RTC_REGISTER_B_BITS;

typedef union {
  RTC_REGISTER_B_BITS Bits;
  UINT8               Data;
} RTC_REGISTER_B;

//
// Register C
//
typedef struct {
  UINT8 Reserved : 4; // Read as zero.  Can not be written.
  UINT8 UF : 1;       // Update End Interrupt Flag
  UINT8 AF : 1;       // Alarm Interrupt Flag
  UINT8 PF : 1;       // Periodic Interrupt Flag
  UINT8 IRQF : 1;     // Iterrupt Request Flag = PF & PIE | AF & AIE | UF & UIE
} RTC_REGISTER_C_BITS;

typedef union {
  RTC_REGISTER_C_BITS Bits;
  UINT8               Data;
} RTC_REGISTER_C;

//
// Register D
//
typedef struct {
  UINT8 Reserved : 7; // Read as zero.  Can not be written.
  UINT8 VRT : 1;      // Valid RAM and Time
} RTC_REGISTER_D_BITS;

typedef union {
  RTC_REGISTER_D_BITS Bits;
  UINT8               Data;
} RTC_REGISTER_D;

#pragma pack()

PC_RTC_GLOBALS mRtc;

BOOLEAN
IsLeapYear (
  IN EFI_TIME   *Time
  )
{
  if (Time->Year % 4 == 0) {
    if (Time->Year % 100 == 0) {
      if (Time->Year % 400 == 0) {
        return TRUE;
      } else {
        return FALSE;
      }
    } else {
      return TRUE;
    }
  } else {
    return FALSE;
  }
}


const INTN  mDayOfMonth[12] = { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

BOOLEAN
DayValid (
  IN  EFI_TIME  *Time
  )
{
  if (Time->Day < 1 ||
      Time->Day > mDayOfMonth[Time->Month - 1] ||
      (Time->Month == 2 && (!IsLeapYear (Time) && Time->Day > 28))
      ) {
    return FALSE;
  }

  return TRUE;
}


UINT8
DecimaltoBcd (
  IN  UINT8 DecValue
  )
{
  UINTN High;
  UINTN Low;

  High  = DecValue / 10;
  Low   = DecValue - (High * 10);

  return (UINT8) (Low + (High << 4));
}

UINT8
BcdToDecimal (
  IN  UINT8 BcdValue
  )
{
  UINTN High;
  UINTN Low;

  High  = BcdValue >> 4;
  Low   = BcdValue - (High << 4);

  return (UINT8) (Low + (High * 10));
}




VOID
ConvertEfiTimeToRtcTime (
  IN EFI_TIME       *Time,
  IN RTC_REGISTER_B RegisterB,
  IN UINT8          *Century
  )
{
  BOOLEAN PM;

  PM = TRUE;
  //
  // Adjust hour field if RTC in in 12 hour mode
  //
  if (RegisterB.Bits.MIL == 0) {
    if (Time->Hour < 12) {
      PM = FALSE;
    }

    if (Time->Hour >= 13) {
      Time->Hour = (UINT8) (Time->Hour - 12);
    } else if (Time->Hour == 0) {
      Time->Hour = 12;
    }
  }
  //
  // Set the Time/Date/Daylight Savings values.
  //
  *Century    = DecimaltoBcd ((UINT8) (Time->Year / 100));

  Time->Year  = (UINT16) (Time->Year % 100);

  if (RegisterB.Bits.DM == 0) {
    Time->Year    = DecimaltoBcd ((UINT8) Time->Year);
    Time->Month   = DecimaltoBcd (Time->Month);
    Time->Day     = DecimaltoBcd (Time->Day);
    Time->Hour    = DecimaltoBcd (Time->Hour);
    Time->Minute  = DecimaltoBcd (Time->Minute);
    Time->Second  = DecimaltoBcd (Time->Second);
  }
  //
  // If we are in 12 hour mode and PM is set, then set bit 7 of the Hour field.
  //
  if (RegisterB.Bits.MIL == 0 && PM) {
    Time->Hour = (UINT8) (Time->Hour | 0x80);
  }
}

/**
  Check the validity of all the fields of a data structure of type EFI_TIME

  @param[in]  Time  Pointer to a data structure of type EFI_TIME that defines a date and time

  @retval  EFI_SUCCESS            All date and time fields are valid
  @retval  EFI_INVALID_PARAMETER  At least one date or time field is not valid
**/
EFI_STATUS
RtcTimeFieldsValid (
  IN EFI_TIME *Time
  )
{
  if ((Time->Year       < 1998     )                      ||
      (Time->Year       > 2099     )                      ||
      (Time->Month      < 1        )                      ||
      (Time->Month      > 12       )                      ||
      (!DayValid (Time))                                  ||
      (Time->Hour       > 23       )                      ||
      (Time->Minute     > 59       )                      ||
      (Time->Second     > 59       )                      ||
      (Time->Nanosecond > 999999999)                      ||
      ((Time->TimeZone != EFI_UNSPECIFIED_TIMEZONE) &&
       ((Time->TimeZone < -1440) ||
        (Time->TimeZone > 1440 )   )                  )  ||
      (Time->Daylight & (~(EFI_TIME_ADJUST_DAYLIGHT |
                           EFI_TIME_IN_DAYLIGHT      )))
      ) {
    return EFI_INVALID_PARAMETER;
  }

  return EFI_SUCCESS;
}

UINT8
RtcRead (
  IN  UINT8 Address
  )
{
  IoWrite8 (PCAT_RTC_ADDRESS_REGISTER, (UINT8) (Address | (UINT8) (IoRead8 (PCAT_RTC_ADDRESS_REGISTER) & 0x80)));
  return IoRead8 (PCAT_RTC_DATA_REGISTER);
}

VOID
RtcWrite (
  IN  UINT8   Address,
  IN  UINT8   Data
  )
{
  IoWrite8 (PCAT_RTC_ADDRESS_REGISTER, (UINT8) (Address | (UINT8) (IoRead8 (PCAT_RTC_ADDRESS_REGISTER) & 0x80)));
  IoWrite8 (PCAT_RTC_DATA_REGISTER, Data);
}


EFI_STATUS
RtcTestCenturyRegister (
  VOID
  )
{
  UINT8 Century;
  UINT8 Temp;

  Century = RtcRead (RTC_ADDRESS_CENTURY);
  //
  //  RtcWrite (RTC_ADDRESS_CENTURY, 0x00);
  //
  Temp = (UINT8) (RtcRead (RTC_ADDRESS_CENTURY) & 0x7f);
  RtcWrite (RTC_ADDRESS_CENTURY, Century);
  if (Temp == 0x19 || Temp == 0x20) {
    return EFI_SUCCESS;
  }

  return EFI_DEVICE_ERROR;
}

VOID
ConvertRtcTimeToEfiTime (
  IN EFI_TIME       *Time,
  IN RTC_REGISTER_B RegisterB
  )
{
  BOOLEAN PM;

  if ((Time->Hour) & 0x80) {
    PM = TRUE;
  } else {
    PM = FALSE;
  }

  Time->Hour = (UINT8) (Time->Hour & 0x7f);

  if (RegisterB.Bits.DM == 0) {
    Time->Year    = BcdToDecimal ((UINT8) Time->Year);
    Time->Month   = BcdToDecimal (Time->Month);
    Time->Day     = BcdToDecimal (Time->Day);
    Time->Hour    = BcdToDecimal (Time->Hour);
    Time->Minute  = BcdToDecimal (Time->Minute);
    Time->Second  = BcdToDecimal (Time->Second);
  }
  //
  // If time is in 12 hour format, convert it to 24 hour format
  //
  if (RegisterB.Bits.MIL == 0) {
    if (PM && Time->Hour < 12) {
      Time->Hour = (UINT8) (Time->Hour + 12);
    }

    if (!PM && Time->Hour == 12) {
      Time->Hour = 0;
    }
  }

  Time->Nanosecond  = 0;
  Time->TimeZone    = EFI_UNSPECIFIED_TIMEZONE;
  Time->Daylight    = 0;
}

EFI_STATUS
RtcWaitToUpdate (
  UINTN Timeout
  )
{
  RTC_REGISTER_A  RegisterA;
  RTC_REGISTER_D  RegisterD;

  //
  // See if the RTC is functioning correctly
  //
  RegisterD.Data = RtcRead (RTC_ADDRESS_REGISTER_D);

  if (RegisterD.Bits.VRT == 0) {
    return EFI_DEVICE_ERROR;
  }
  //
  // Wait for up to 0.1 seconds for the RTC to be ready.
  //
  Timeout         = (Timeout / 10) + 1;
  RegisterA.Data  = RtcRead (RTC_ADDRESS_REGISTER_A);
  while (RegisterA.Bits.UIP == 1 && Timeout > 0) {
    MicroSecondDelay (10);
    RegisterA.Data = RtcRead (RTC_ADDRESS_REGISTER_A);
    Timeout--;
  }

  RegisterD.Data = RtcRead (RTC_ADDRESS_REGISTER_D);
  if (Timeout == 0 || RegisterD.Bits.VRT == 0) {
    return EFI_DEVICE_ERROR;
  }

  return EFI_SUCCESS;
}

EFI_STATUS
LibGetTime (
  OUT EFI_TIME                *Time,
  OUT  EFI_TIME_CAPABILITIES  *Capabilities
  )
{
  EFI_STATUS      Status;
  RTC_REGISTER_B  RegisterB;
  UINT8           Century;
  UINTN           BufferSize;

  //
  // Check parameters for null pointer
  //
  if (Time == NULL) {
    return EFI_INVALID_PARAMETER;

  }
  //
  // Acquire RTC Lock to make access to RTC atomic
  //
  EfiAcquireLock (&mRtc.RtcLock);

  //
  // Wait for up to 0.1 seconds for the RTC to be updated
  //
  Status = RtcWaitToUpdate (100000);
  if (EFI_ERROR (Status)) {
    EfiReleaseLock (&mRtc.RtcLock);
    return Status;
  }
  //
  // Read Register B
  //
  RegisterB.Data = RtcRead (RTC_ADDRESS_REGISTER_B);

  //
  // Get the Time/Date/Daylight Savings values.
  //
  Time->Second  = RtcRead (RTC_ADDRESS_SECONDS);
  Time->Minute  = RtcRead (RTC_ADDRESS_MINUTES);
  Time->Hour    = RtcRead (RTC_ADDRESS_HOURS);
  Time->Day     = RtcRead (RTC_ADDRESS_DAY_OF_THE_MONTH);
  Time->Month   = RtcRead (RTC_ADDRESS_MONTH);
  Time->Year    = RtcRead (RTC_ADDRESS_YEAR);

  ConvertRtcTimeToEfiTime (Time, RegisterB);

  if (RtcTestCenturyRegister () == EFI_SUCCESS) {
    Century = BcdToDecimal ((UINT8) (RtcRead (RTC_ADDRESS_CENTURY) & 0x7f));
  } else {
    Century = BcdToDecimal (RtcRead (RTC_ADDRESS_CENTURY));
  }

  Time->Year = (UINT16) (Century * 100 + Time->Year);

  //
  // Release RTC Lock.
  //
  EfiReleaseLock (&mRtc.RtcLock);

  //
  // Get the variable that containts the TimeZone and Daylight fields
  //
  Time->TimeZone  = mRtc.SavedTimeZone;
  Time->Daylight  = mRtc.Daylight;

  BufferSize      = sizeof (INT16) + sizeof (UINT8);

  //
  // Make sure all field values are in correct range
  //
  Status = RtcTimeFieldsValid (Time);
  if (EFI_ERROR (Status)) {
    return EFI_DEVICE_ERROR;
  }
  //
  //  Fill in Capabilities if it was passed in
  //
  if (Capabilities) {
    Capabilities->Resolution = 1;
    //
    // 1 hertz
    //
    Capabilities->Accuracy = 50000000;
    //
    // 50 ppm
    //
    Capabilities->SetsToZero = FALSE;
  }

  return EFI_SUCCESS;
}



EFI_STATUS
LibSetTime (
  IN EFI_TIME                *Time
  )
{
  EFI_STATUS      Status;
  EFI_TIME        RtcTime;
  RTC_REGISTER_B  RegisterB;
  UINT8           Century;

  if (Time == NULL) {
    return EFI_INVALID_PARAMETER;
  }
  //
  // Make sure that the time fields are valid
  //
  Status = RtcTimeFieldsValid (Time);
  if (EFI_ERROR (Status)) {
    return Status;
  }

  CopyMem (&RtcTime, Time, sizeof (EFI_TIME));

  //
  // Acquire RTC Lock to make access to RTC atomic
  //
  EfiAcquireLock (&mRtc.RtcLock);

  //
  // Wait for up to 0.1 seconds for the RTC to be updated
  //
  Status = RtcWaitToUpdate (100000);
  if (EFI_ERROR (Status)) {
    EfiReleaseLock (&mRtc.RtcLock);
    return Status;
  }
  //
  // Read Register B, and inhibit updates of the RTC
  //
  RegisterB.Data      = RtcRead (RTC_ADDRESS_REGISTER_B);
  RegisterB.Bits.SET  = 1;
  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);

  ConvertEfiTimeToRtcTime (&RtcTime, RegisterB, &Century);

  RtcWrite (RTC_ADDRESS_SECONDS, RtcTime.Second);
  RtcWrite (RTC_ADDRESS_MINUTES, RtcTime.Minute);
  RtcWrite (RTC_ADDRESS_HOURS, RtcTime.Hour);
  RtcWrite (RTC_ADDRESS_DAY_OF_THE_MONTH, RtcTime.Day);
  RtcWrite (RTC_ADDRESS_MONTH, RtcTime.Month);
  RtcWrite (RTC_ADDRESS_YEAR, (UINT8) RtcTime.Year);
  if (RtcTestCenturyRegister () == EFI_SUCCESS) {
    Century = (UINT8) ((Century & 0x7f) | (RtcRead (RTC_ADDRESS_CENTURY) & 0x80));
  }

  RtcWrite (RTC_ADDRESS_CENTURY, Century);

  //
  // Allow updates of the RTC registers
  //
  RegisterB.Bits.SET = 0;
  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);

  //
  // Release RTC Lock.
  //
  EfiReleaseLock (&mRtc.RtcLock);

  //
  // Set the variable that containts the TimeZone and Daylight fields
  //
  mRtc.SavedTimeZone = Time->TimeZone;
  mRtc.Daylight      = Time->Daylight;
  return Status;
}

EFI_STATUS
libGetWakeupTime (
  OUT BOOLEAN     *Enabled,
  OUT BOOLEAN     *Pending,
  OUT EFI_TIME    *Time
  )
{
  EFI_STATUS      Status;
  RTC_REGISTER_B  RegisterB;
  RTC_REGISTER_C  RegisterC;
  UINT8           Century;

  //
  // Check parameters for null pointers
  //
  if ((Enabled == NULL) || (Pending == NULL) || (Time == NULL)) {
    return EFI_INVALID_PARAMETER;

  }
  //
  // Acquire RTC Lock to make access to RTC atomic
  //
  EfiAcquireLock (&mRtc.RtcLock);

  //
  // Wait for up to 0.1 seconds for the RTC to be updated
  //
  Status = RtcWaitToUpdate (100000);
  if (EFI_ERROR (Status)) {
    EfiReleaseLock (&mRtc.RtcLock);
    return EFI_DEVICE_ERROR;
  }
  //
  // Read Register B and Register C
  //
  RegisterB.Data  = RtcRead (RTC_ADDRESS_REGISTER_B);
  RegisterC.Data  = RtcRead (RTC_ADDRESS_REGISTER_C);

  //
  // Get the Time/Date/Daylight Savings values.
  //
  *Enabled = RegisterB.Bits.AIE;
  if (*Enabled) {
    Time->Second  = RtcRead (RTC_ADDRESS_SECONDS_ALARM);
    Time->Minute  = RtcRead (RTC_ADDRESS_MINUTES_ALARM);
    Time->Hour    = RtcRead (RTC_ADDRESS_HOURS_ALARM);
    Time->Day     = RtcRead (RTC_ADDRESS_DAY_OF_THE_MONTH);
    Time->Month   = RtcRead (RTC_ADDRESS_MONTH);
    Time->Year    = RtcRead (RTC_ADDRESS_YEAR);
  } else {
    Time->Second  = 0;
    Time->Minute  = 0;
    Time->Hour    = 0;
    Time->Day     = RtcRead (RTC_ADDRESS_DAY_OF_THE_MONTH);
    Time->Month   = RtcRead (RTC_ADDRESS_MONTH);
    Time->Year    = RtcRead (RTC_ADDRESS_YEAR);
  }

  ConvertRtcTimeToEfiTime (Time, RegisterB);

  if (RtcTestCenturyRegister () == EFI_SUCCESS) {
    Century = BcdToDecimal ((UINT8) (RtcRead (RTC_ADDRESS_CENTURY) & 0x7f));
  } else {
    Century = BcdToDecimal (RtcRead (RTC_ADDRESS_CENTURY));
  }

  Time->Year = (UINT16) (Century * 100 + Time->Year);

  //
  // Release RTC Lock.
  //
  EfiReleaseLock (&mRtc.RtcLock);

  //
  // Make sure all field values are in correct range
  //
  Status = RtcTimeFieldsValid (Time);
  if (EFI_ERROR (Status)) {
    return EFI_DEVICE_ERROR;
  }

  *Pending = RegisterC.Bits.AF;

  return EFI_SUCCESS;
}

EFI_STATUS
LibSetWakeupTime (
  IN BOOLEAN      Enabled,
  OUT EFI_TIME    *Time
  )
{
  EFI_STATUS            Status;
  EFI_TIME              RtcTime;
  RTC_REGISTER_B        RegisterB;
  UINT8                 Century;
  EFI_TIME_CAPABILITIES Capabilities;

  if (Enabled) {

    if (Time == NULL) {
      return EFI_INVALID_PARAMETER;
    }
    //
    // Make sure that the time fields are valid
    //
    Status = RtcTimeFieldsValid (Time);
    if (EFI_ERROR (Status)) {
      return EFI_INVALID_PARAMETER;
    }
    //
    // Just support set alarm time within 24 hours
    //
    LibGetTime (&RtcTime, &Capabilities);
    if (Time->Year != RtcTime.Year ||
        Time->Month != RtcTime.Month ||
        (Time->Day != RtcTime.Day && Time->Day != (RtcTime.Day + 1))
        ) {
      return EFI_UNSUPPORTED;
    }
    //
    // Make a local copy of the time and date
    //
    CopyMem (&RtcTime, Time, sizeof (EFI_TIME));

  }
  //
  // Acquire RTC Lock to make access to RTC atomic
  //
  EfiAcquireLock (&mRtc.RtcLock);

  //
  // Wait for up to 0.1 seconds for the RTC to be updated
  //
  Status = RtcWaitToUpdate (100000);
  if (EFI_ERROR (Status)) {
    EfiReleaseLock (&mRtc.RtcLock);
    return EFI_DEVICE_ERROR;
  }
  //
  // Read Register B, and inhibit updates of the RTC
  //
  RegisterB.Data      = RtcRead (RTC_ADDRESS_REGISTER_B);

  RegisterB.Bits.SET  = 1;
  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);

  if (Enabled) {
    ConvertEfiTimeToRtcTime (&RtcTime, RegisterB, &Century);

    //
    // Set RTC alarm time
    //
    RtcWrite (RTC_ADDRESS_SECONDS_ALARM, RtcTime.Second);
    RtcWrite (RTC_ADDRESS_MINUTES_ALARM, RtcTime.Minute);
    RtcWrite (RTC_ADDRESS_HOURS_ALARM, RtcTime.Hour);

    RegisterB.Bits.AIE = 1;

  } else {
    RegisterB.Bits.AIE = 0;
  }
  //
  // Allow updates of the RTC registers
  //
  RegisterB.Bits.SET = 0;
  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);

  //
  // Release RTC Lock.
  //
  EfiReleaseLock (&mRtc.RtcLock);

  return EFI_SUCCESS;
}



VOID
LibRtcVirtualAddressChangeEvent (
  VOID
  )
{
}


VOID
LibRtcInitialize (
  VOID
  )
{
  EFI_STATUS      Status;
  RTC_REGISTER_A  RegisterA;
  RTC_REGISTER_B  RegisterB;
  RTC_REGISTER_C  RegisterC;
  RTC_REGISTER_D  RegisterD;
  UINT8           Century;
  EFI_TIME        Time;

  //
  // Acquire RTC Lock to make access to RTC atomic
  //
  EfiAcquireLock (&mRtc.RtcLock);

  //
  // Initialize RTC Register
  //
  // Make sure Division Chain is properly configured,
  // or RTC clock won't "tick" -- time won't increment
  //
  RegisterA.Data = RTC_INIT_REGISTER_A;
  RtcWrite (RTC_ADDRESS_REGISTER_A, RegisterA.Data);

  //
  // Read Register B
  //
  RegisterB.Data = RtcRead (RTC_ADDRESS_REGISTER_B);

  //
  // Clear RTC flag register
  //
  RegisterC.Data = RtcRead (RTC_ADDRESS_REGISTER_C);

  //
  // Clear RTC register D
  //
  RegisterD.Data = RTC_INIT_REGISTER_D;
  RtcWrite (RTC_ADDRESS_REGISTER_D, RegisterD.Data);

  //
  // Wait for up to 0.1 seconds for the RTC to be updated
  //
  Status = RtcWaitToUpdate (100000);
  if (EFI_ERROR (Status)) {
    EfiReleaseLock (&mRtc.RtcLock);
    return;
  }

  //
  // Get the Time/Date/Daylight Savings values.
  //
  Time.Second = RtcRead (RTC_ADDRESS_SECONDS);
  Time.Minute = RtcRead (RTC_ADDRESS_MINUTES);
  Time.Hour   = RtcRead (RTC_ADDRESS_HOURS);
  Time.Day    = RtcRead (RTC_ADDRESS_DAY_OF_THE_MONTH);
  Time.Month  = RtcRead (RTC_ADDRESS_MONTH);
  Time.Year   = RtcRead (RTC_ADDRESS_YEAR);

  ConvertRtcTimeToEfiTime (&Time, RegisterB);

  if (RtcTestCenturyRegister () == EFI_SUCCESS) {
    Century = BcdToDecimal ((UINT8) (RtcRead (RTC_ADDRESS_CENTURY) & 0x7f));
  } else {
    Century = BcdToDecimal (RtcRead (RTC_ADDRESS_CENTURY));
  }

  Time.Year = (UINT16) (Century * 100 + Time.Year);

  //
  // Set RTC configuration after get original time
  //
  RtcWrite (RTC_ADDRESS_REGISTER_B, RTC_INIT_REGISTER_B);

  //
  // Release RTC Lock.
  //
  EfiReleaseLock (&mRtc.RtcLock);

  //
  // Validate time fields
  //
  Status = RtcTimeFieldsValid (&Time);
  if (EFI_ERROR (Status)) {
    Time.Second = RTC_INIT_SECOND;
    Time.Minute = RTC_INIT_MINUTE;
    Time.Hour   = RTC_INIT_HOUR;
    Time.Day    = RTC_INIT_DAY;
    Time.Month  = RTC_INIT_MONTH;
    Time.Year   = RTC_INIT_YEAR;
  }
  //
  // Reset time value according to new RTC configuration
  //
  LibSetTime (&Time);

  return;
}