/** @file
  RTC Architectural Protocol GUID as defined in DxeCis 0.96.

Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
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.

**/

#include "PcRtc.h"

//
// Days of month.
//
UINTN mDayOfMonth[] = { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

//
// The name of NV variable to store the timezone and daylight saving information.
//
CHAR16 mTimeZoneVariableName[] = L"RTC";

/**
  Compare the Hour, Minute and Second of the From time and the To time.
  
  Only compare H/M/S in EFI_TIME and ignore other fields here.

  @param From   the first time
  @param To     the second time

  @return  >0   The H/M/S of the From time is later than those of To time
  @return  ==0  The H/M/S of the From time is same as those of To time
  @return  <0   The H/M/S of the From time is earlier than those of To time
**/
INTN
CompareHMS (
  IN EFI_TIME   *From,
  IN EFI_TIME   *To
  );

/**
  To check if second date is later than first date within 24 hours.

  @param  From   the first date
  @param  To     the second date

  @retval TRUE   From is previous to To within 24 hours.
  @retval FALSE  From is later, or it is previous to To more than 24 hours.
**/
BOOLEAN
IsWithinOneDay (
  IN EFI_TIME   *From,
  IN EFI_TIME   *To
  );

/**
  Read RTC content through its registers.

  @param  Address  Address offset of RTC. It is recommended to use macros such as
                   RTC_ADDRESS_SECONDS.

  @return The data of UINT8 type read from RTC.
**/
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);
}

/**
  Write RTC through its registers.

  @param  Address  Address offset of RTC. It is recommended to use macros such as
                   RTC_ADDRESS_SECONDS.
  @param  Data     The content you want to write into RTC.

**/
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);
}

/**
  Initialize RTC.

  @param  Global            For global use inside this module.

  @retval EFI_DEVICE_ERROR  Initialization failed due to device error.
  @retval EFI_SUCCESS       Initialization successful.

**/
EFI_STATUS
PcRtcInit (
  IN PC_RTC_MODULE_GLOBALS  *Global
  )
{
  EFI_STATUS      Status;
  RTC_REGISTER_A  RegisterA;
  RTC_REGISTER_B  RegisterB;
  RTC_REGISTER_D  RegisterD;
  EFI_TIME        Time;
  UINTN           DataSize;
  UINT32          TimerVar;
  BOOLEAN         Enabled;
  BOOLEAN         Pending;

  //
  // Acquire RTC Lock to make access to RTC atomic
  //
  if (!EfiAtRuntime ()) {
    EfiAcquireLock (&Global->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
  //
  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 (PcdGet32 (PcdRealTimeClockUpdateTimeout));
  if (EFI_ERROR (Status)) {
    //
    // Set the variable with default value if the RTC is functioning incorrectly.
    //
    Global->SavedTimeZone = EFI_UNSPECIFIED_TIMEZONE;
    Global->Daylight      = 0;
    if (!EfiAtRuntime ()) {
      EfiReleaseLock (&Global->RtcLock);
    }
    return EFI_DEVICE_ERROR;
  }
  //
  // 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);

  //
  // Set RTC configuration after get original time
  // The value of bit AIE should be reserved.
  //
  RegisterB.Data = RTC_INIT_REGISTER_B | (RegisterB.Data & BIT5);
  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);

  //
  // Release RTC Lock.
  //
  if (!EfiAtRuntime ()) {
    EfiReleaseLock (&Global->RtcLock);
  }
 
  //
  // Get the data of Daylight saving and time zone, if they have been
  // stored in NV variable during previous boot.
  //
  DataSize = sizeof (UINT32);
  Status = EfiGetVariable (
             mTimeZoneVariableName,
             &gEfiCallerIdGuid,
             NULL,
             &DataSize,
             &TimerVar
             );
  if (!EFI_ERROR (Status)) {
    Time.TimeZone = (INT16) TimerVar;
    Time.Daylight = (UINT8) (TimerVar >> 16);
  } else {
    Time.TimeZone = EFI_UNSPECIFIED_TIMEZONE;
    Time.Daylight = 0;  
  }

  //
  // Validate time fields
  //
  Status = ConvertRtcTimeToEfiTime (&Time, RegisterB);
  if (!EFI_ERROR (Status)) {
    Status = RtcTimeFieldsValid (&Time);
  }
  if (EFI_ERROR (Status)) {
    //
    // Report Status Code to indicate that the RTC has bad date and time
    //
    REPORT_STATUS_CODE (
      EFI_ERROR_CODE | EFI_ERROR_MINOR,
      (EFI_SOFTWARE_DXE_RT_DRIVER | EFI_SW_EC_BAD_DATE_TIME)
      );
    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   = PcdGet16 (PcdMinimalValidYear);
    Time.Nanosecond  = 0;
    Time.TimeZone = EFI_UNSPECIFIED_TIMEZONE;
    Time.Daylight = 0;
  }

  //
  // Reset time value according to new RTC configuration
  //
  Status = PcRtcSetTime (&Time, Global);
  if (EFI_ERROR (Status)) {
    return EFI_DEVICE_ERROR;
  }
  
  //
  // Reset wakeup time value to valid state when wakeup alarm is disabled and wakeup time is invalid.
  // Global variable has already had valid SavedTimeZone and Daylight,
  // so we can use them to get and set wakeup time.
  //
  Status = PcRtcGetWakeupTime (&Enabled, &Pending, &Time, Global);
  if ((Enabled) || (!EFI_ERROR (Status))) {
    return EFI_SUCCESS;
  }
  
  //
  // When wakeup time is disabled and invalid, reset wakeup time register to valid state 
  // but keep wakeup alarm disabled.
  //
  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   = PcdGet16 (PcdMinimalValidYear);
  Time.Nanosecond  = 0;
  Time.TimeZone = Global->SavedTimeZone;
  Time.Daylight = Global->Daylight;;

  //
  // Acquire RTC Lock to make access to RTC atomic
  //
  if (!EfiAtRuntime ()) {
    EfiAcquireLock (&Global->RtcLock);
  }
  //
  // Wait for up to 0.1 seconds for the RTC to be updated
  //
  Status = RtcWaitToUpdate (PcdGet32 (PcdRealTimeClockUpdateTimeout));
  if (EFI_ERROR (Status)) {
    if (!EfiAtRuntime ()) {
    EfiReleaseLock (&Global->RtcLock);
    }
    return EFI_DEVICE_ERROR;
  }

  ConvertEfiTimeToRtcTime (&Time, RegisterB);

  //
  // Set the Y/M/D info to variable as it has no corresponding hw registers.
  //
  Status =  EfiSetVariable (
              L"RTCALARM",
              &gEfiCallerIdGuid,
              EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS | EFI_VARIABLE_NON_VOLATILE,
              sizeof (Time),
              &Time
              );
  if (EFI_ERROR (Status)) {
    if (!EfiAtRuntime ()) {
      EfiReleaseLock (&Global->RtcLock);
    }
    return EFI_DEVICE_ERROR;
  }
  
  //
  // Inhibit updates of the RTC
  //
  RegisterB.Bits.Set  = 1;
  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);
 
  //
  // Set RTC alarm time registers
  //
  RtcWrite (RTC_ADDRESS_SECONDS_ALARM, Time.Second);
  RtcWrite (RTC_ADDRESS_MINUTES_ALARM, Time.Minute);
  RtcWrite (RTC_ADDRESS_HOURS_ALARM, Time.Hour);

  //
  // Allow updates of the RTC registers
  //
  RegisterB.Bits.Set = 0;
  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);
 
  //
  // Release RTC Lock.
  //
  if (!EfiAtRuntime ()) {
    EfiReleaseLock (&Global->RtcLock);
  }
  return EFI_SUCCESS;
}

/**
  Returns the current time and date information, and the time-keeping capabilities
  of the hardware platform.

  @param  Time          A pointer to storage to receive a snapshot of the current time.
  @param  Capabilities  An optional pointer to a buffer to receive the real time clock
                        device's capabilities.
  @param  Global        For global use inside this module.

  @retval EFI_SUCCESS            The operation completed successfully.
  @retval EFI_INVALID_PARAMETER  Time is NULL.
  @retval EFI_DEVICE_ERROR       The time could not be retrieved due to hardware error.

**/
EFI_STATUS
PcRtcGetTime (
  OUT  EFI_TIME               *Time,
  OUT  EFI_TIME_CAPABILITIES  *Capabilities,  OPTIONAL
  IN   PC_RTC_MODULE_GLOBALS  *Global
  )
{
  EFI_STATUS      Status;
  RTC_REGISTER_B  RegisterB;

  //
  // Check parameters for null pointer
  //
  if (Time == NULL) {
    return EFI_INVALID_PARAMETER;

  }
  //
  // Acquire RTC Lock to make access to RTC atomic
  //
  if (!EfiAtRuntime ()) {
    EfiAcquireLock (&Global->RtcLock);
  }
  //
  // Wait for up to 0.1 seconds for the RTC to be updated
  //
  Status = RtcWaitToUpdate (PcdGet32 (PcdRealTimeClockUpdateTimeout));
  if (EFI_ERROR (Status)) {
      if (!EfiAtRuntime ()) {
        EfiReleaseLock (&Global->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);

  //
  // Release RTC Lock.
  //
  if (!EfiAtRuntime ()) {
    EfiReleaseLock (&Global->RtcLock);
  }

  //
  // Get the variable that contains the TimeZone and Daylight fields
  //
  Time->TimeZone  = Global->SavedTimeZone;
  Time->Daylight  = Global->Daylight;

  //
  // Make sure all field values are in correct range
  //
  Status = ConvertRtcTimeToEfiTime (Time, RegisterB);
  if (!EFI_ERROR (Status)) {
    Status = RtcTimeFieldsValid (Time);
  }
  if (EFI_ERROR (Status)) {
    return EFI_DEVICE_ERROR;
  }

  //
  //  Fill in Capabilities if it was passed in
  //
  if (Capabilities != NULL) {
    Capabilities->Resolution = 1;
    //
    // 1 hertz
    //
    Capabilities->Accuracy = 50000000;
    //
    // 50 ppm
    //
    Capabilities->SetsToZero = FALSE;
  }

  return EFI_SUCCESS;
}

/**
  Sets the current local time and date information.

  @param  Time                  A pointer to the current time.
  @param  Global                For global use inside this module.

  @retval EFI_SUCCESS           The operation completed successfully.
  @retval EFI_INVALID_PARAMETER A time field is out of range.
  @retval EFI_DEVICE_ERROR      The time could not be set due due to hardware error.

**/
EFI_STATUS
PcRtcSetTime (
  IN EFI_TIME                *Time,
  IN PC_RTC_MODULE_GLOBALS   *Global
  )
{
  EFI_STATUS      Status;
  EFI_TIME        RtcTime;
  RTC_REGISTER_B  RegisterB;
  UINT32          TimerVar;

  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
  //
  if (!EfiAtRuntime ()) {
    EfiAcquireLock (&Global->RtcLock);
  }
  //
  // Wait for up to 0.1 seconds for the RTC to be updated
  //
  Status = RtcWaitToUpdate (PcdGet32 (PcdRealTimeClockUpdateTimeout));
  if (EFI_ERROR (Status)) {
     if (!EfiAtRuntime ()) {
       EfiReleaseLock (&Global->RtcLock);
     }
    return Status;
  }
  
  //
  // Write timezone and daylight to RTC variable
  //
  if (Time->TimeZone == EFI_UNSPECIFIED_TIMEZONE) {
    Status = EfiSetVariable (
               mTimeZoneVariableName,
               &gEfiCallerIdGuid,
               0,
               0,
               NULL
               );
    if (Status == EFI_NOT_FOUND) {
      Status = EFI_SUCCESS;
    }
  } else {
    TimerVar = Time->Daylight;
    TimerVar = (UINT32) ((TimerVar << 16) | (UINT16)(Time->TimeZone));
    Status = EfiSetVariable (
               mTimeZoneVariableName,
               &gEfiCallerIdGuid,
               EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS | EFI_VARIABLE_NON_VOLATILE,
               sizeof (TimerVar),
               &TimerVar
               );
  }

  if (EFI_ERROR (Status)) {
    if (!EfiAtRuntime ()) {
      EfiReleaseLock (&Global->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);

  //
  // Store the century value to RTC before converting to BCD format.
  //
  if (Global->CenturyRtcAddress != 0) {
    RtcWrite (Global->CenturyRtcAddress, DecimalToBcd8 ((UINT8) (RtcTime.Year / 100)));
  }

  ConvertEfiTimeToRtcTime (&RtcTime, RegisterB);

  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);

  //
  // Allow updates of the RTC registers
  //
  RegisterB.Bits.Set = 0;
  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);

  //
  // Release RTC Lock.
  //
  if (!EfiAtRuntime ()) {
    EfiReleaseLock (&Global->RtcLock);
  }
  //
  // Set the variable that contains the TimeZone and Daylight fields
  //
  Global->SavedTimeZone = Time->TimeZone;
  Global->Daylight      = Time->Daylight;

  return EFI_SUCCESS;
}

/**
  Returns the current wakeup alarm clock setting.

  @param  Enabled  Indicates if the alarm is currently enabled or disabled.
  @param  Pending  Indicates if the alarm signal is pending and requires acknowledgment.
  @param  Time     The current alarm setting.
  @param  Global   For global use inside this module.

  @retval EFI_SUCCESS           The alarm settings were returned.
  @retval EFI_INVALID_PARAMETER Enabled is NULL.
  @retval EFI_INVALID_PARAMETER Pending is NULL.
  @retval EFI_INVALID_PARAMETER Time is NULL.
  @retval EFI_DEVICE_ERROR      The wakeup time could not be retrieved due to a hardware error.
  @retval EFI_UNSUPPORTED       A wakeup timer is not supported on this platform.

**/
EFI_STATUS
PcRtcGetWakeupTime (
  OUT BOOLEAN                *Enabled,
  OUT BOOLEAN                *Pending,
  OUT EFI_TIME               *Time,
  IN  PC_RTC_MODULE_GLOBALS  *Global
  )
{
  EFI_STATUS      Status;
  RTC_REGISTER_B  RegisterB;
  RTC_REGISTER_C  RegisterC;
  EFI_TIME        RtcTime;
  UINTN           DataSize;

  //
  // 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
  //
  if (!EfiAtRuntime ()) {
    EfiAcquireLock (&Global->RtcLock);
  }
  //
  // Wait for up to 0.1 seconds for the RTC to be updated
  //
  Status = RtcWaitToUpdate (PcdGet32 (PcdRealTimeClockUpdateTimeout));
  if (EFI_ERROR (Status)) {
    if (!EfiAtRuntime ()) {
    EfiReleaseLock (&Global->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;
  *Pending = RegisterC.Bits.Af;

  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);
  Time->TimeZone = Global->SavedTimeZone;
  Time->Daylight = Global->Daylight;

  //
  // Get the alarm info from variable
  //
  DataSize = sizeof (EFI_TIME);
  Status = EfiGetVariable (
              L"RTCALARM",
              &gEfiCallerIdGuid,
              NULL,
              &DataSize,
              &RtcTime
              );
  if (!EFI_ERROR (Status)) {
    //
    // The alarm variable exists. In this case, we read variable to get info.
    //
    Time->Day   = RtcTime.Day;
    Time->Month = RtcTime.Month;
    Time->Year  = RtcTime.Year;
  }

  //
  // Release RTC Lock.
  //
  if (!EfiAtRuntime ()) {
    EfiReleaseLock (&Global->RtcLock);
  }

  //
  // Make sure all field values are in correct range
  //
  Status = ConvertRtcTimeToEfiTime (Time, RegisterB);
  if (!EFI_ERROR (Status)) {
    Status = RtcTimeFieldsValid (Time);
  }
  if (EFI_ERROR (Status)) {
    return EFI_DEVICE_ERROR;
  }

  return EFI_SUCCESS;
}

/**
  Sets the system wakeup alarm clock time.

  @param  Enabled  Enable or disable the wakeup alarm.
  @param  Time     If Enable is TRUE, the time to set the wakeup alarm for.
                   If Enable is FALSE, then this parameter is optional, and may be NULL.
  @param  Global   For global use inside this module.

  @retval EFI_SUCCESS           If Enable is TRUE, then the wakeup alarm was enabled.
                                If Enable is FALSE, then the wakeup alarm was disabled.
  @retval EFI_INVALID_PARAMETER A time field is out of range.
  @retval EFI_DEVICE_ERROR      The wakeup time could not be set due to a hardware error.
  @retval EFI_UNSUPPORTED       A wakeup timer is not supported on this platform.

**/
EFI_STATUS
PcRtcSetWakeupTime (
  IN BOOLEAN                Enable,
  IN EFI_TIME               *Time,   OPTIONAL
  IN PC_RTC_MODULE_GLOBALS  *Global
  )
{
  EFI_STATUS            Status;
  EFI_TIME              RtcTime;
  RTC_REGISTER_B        RegisterB;
  EFI_TIME_CAPABILITIES Capabilities;

  ZeroMem (&RtcTime, sizeof (RtcTime));

  if (Enable) {

    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
    //
    PcRtcGetTime (&RtcTime, &Capabilities, Global);
    Status = RtcTimeFieldsValid (&RtcTime);
    if (EFI_ERROR (Status)) {
      return EFI_DEVICE_ERROR;
    }
    if (!IsWithinOneDay (&RtcTime, Time)) {
      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
  //
  if (!EfiAtRuntime ()) {
    EfiAcquireLock (&Global->RtcLock);
  }
  //
  // Wait for up to 0.1 seconds for the RTC to be updated
  //
  Status = RtcWaitToUpdate (PcdGet32 (PcdRealTimeClockUpdateTimeout));
  if (EFI_ERROR (Status)) {
    if (!EfiAtRuntime ()) {
    EfiReleaseLock (&Global->RtcLock);
    }
    return EFI_DEVICE_ERROR;
  }
  //
  // Read Register B
  //
  RegisterB.Data = RtcRead (RTC_ADDRESS_REGISTER_B);

  if (Enable) {
    ConvertEfiTimeToRtcTime (&RtcTime, RegisterB);
  } else {
    //
    // if the alarm is disable, record the current setting.
    //
    RtcTime.Second  = RtcRead (RTC_ADDRESS_SECONDS_ALARM);
    RtcTime.Minute  = RtcRead (RTC_ADDRESS_MINUTES_ALARM);
    RtcTime.Hour    = RtcRead (RTC_ADDRESS_HOURS_ALARM);
    RtcTime.Day     = RtcRead (RTC_ADDRESS_DAY_OF_THE_MONTH);
    RtcTime.Month   = RtcRead (RTC_ADDRESS_MONTH);
    RtcTime.Year    = RtcRead (RTC_ADDRESS_YEAR);
    RtcTime.TimeZone = Global->SavedTimeZone;
    RtcTime.Daylight = Global->Daylight;
  }

  //
  // Set the Y/M/D info to variable as it has no corresponding hw registers.
  //
  Status =  EfiSetVariable (
              L"RTCALARM",
              &gEfiCallerIdGuid,
              EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS | EFI_VARIABLE_NON_VOLATILE,
              sizeof (RtcTime),
              &RtcTime
              );
  if (EFI_ERROR (Status)) {
    if (!EfiAtRuntime ()) {
      EfiReleaseLock (&Global->RtcLock);
    }
    return EFI_DEVICE_ERROR;
  }
  
  //
  // Inhibit updates of the RTC
  //
  RegisterB.Bits.Set  = 1;
  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);

  if (Enable) {
    //
    // 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.
  //
  if (!EfiAtRuntime ()) {
    EfiReleaseLock (&Global->RtcLock);
  }
  return EFI_SUCCESS;
}


/**
  Checks an 8-bit BCD value, and converts to an 8-bit value if valid.

  This function checks the 8-bit BCD value specified by Value.
  If valid, the function converts it to an 8-bit value and returns it.
  Otherwise, return 0xff.

  @param   Value The 8-bit BCD value to check and convert

  @return  The 8-bit value converted. Or 0xff if Value is invalid.

**/
UINT8
CheckAndConvertBcd8ToDecimal8 (
  IN  UINT8  Value
  )
{
  if ((Value < 0xa0) && ((Value & 0xf) < 0xa)) {
    return BcdToDecimal8 (Value);
  }

  return 0xff;
}

/**
  Converts time read from RTC to EFI_TIME format defined by UEFI spec.

  This function converts raw time data read from RTC to the EFI_TIME format
  defined by UEFI spec.
  If data mode of RTC is BCD, then converts it to decimal,
  If RTC is in 12-hour format, then converts it to 24-hour format.

  @param   Time       On input, the time data read from RTC to convert
                      On output, the time converted to UEFI format
  @param   RegisterB  Value of Register B of RTC, indicating data mode
                      and hour format.

  @retval  EFI_INVALID_PARAMETER  Parameters passed in are invalid.
  @retval  EFI_SUCCESS            Convert RTC time to EFI time successfully.

**/
EFI_STATUS
ConvertRtcTimeToEfiTime (
  IN OUT EFI_TIME        *Time,
  IN     RTC_REGISTER_B  RegisterB
  )
{
  BOOLEAN IsPM;
  UINT8   Century;

  if ((Time->Hour & 0x80) != 0) {
    IsPM = TRUE;
  } else {
    IsPM = FALSE;
  }

  Time->Hour = (UINT8) (Time->Hour & 0x7f);

  if (RegisterB.Bits.Dm == 0) {
    Time->Year    = CheckAndConvertBcd8ToDecimal8 ((UINT8) Time->Year);
    Time->Month   = CheckAndConvertBcd8ToDecimal8 (Time->Month);
    Time->Day     = CheckAndConvertBcd8ToDecimal8 (Time->Day);
    Time->Hour    = CheckAndConvertBcd8ToDecimal8 (Time->Hour);
    Time->Minute  = CheckAndConvertBcd8ToDecimal8 (Time->Minute);
    Time->Second  = CheckAndConvertBcd8ToDecimal8 (Time->Second);
  }

  if (Time->Year == 0xff || Time->Month == 0xff || Time->Day == 0xff ||
      Time->Hour == 0xff || Time->Minute == 0xff || Time->Second == 0xff) {
    return EFI_INVALID_PARAMETER;
  }

  //
  // For minimal/maximum year range [1970, 2069],
  //   Century is 19 if RTC year >= 70,
  //   Century is 20 otherwise.
  //
  Century = (UINT8) (PcdGet16 (PcdMinimalValidYear) / 100);
  if (Time->Year < PcdGet16 (PcdMinimalValidYear) % 100) {
    Century++;
  }
  Time->Year = (UINT16) (Century * 100 + Time->Year);

  //
  // If time is in 12 hour format, convert it to 24 hour format
  //
  if (RegisterB.Bits.Mil == 0) {
    if (IsPM && Time->Hour < 12) {
      Time->Hour = (UINT8) (Time->Hour + 12);
    }

    if (!IsPM && Time->Hour == 12) {
      Time->Hour = 0;
    }
  }

  Time->Nanosecond  = 0;

  return EFI_SUCCESS;
}

/**
  Wait for a period for the RTC to be ready.

  @param    Timeout  Tell how long it should take to wait.

  @retval   EFI_DEVICE_ERROR   RTC device error.
  @retval   EFI_SUCCESS        RTC is updated and ready.  
**/
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;
}

/**
  See if all fields of a variable of EFI_TIME type is correct.

  @param   Time   The time to be checked.

  @retval  EFI_INVALID_PARAMETER  Some fields of Time are not correct.
  @retval  EFI_SUCCESS            Time is a valid EFI_TIME variable.

**/
EFI_STATUS
RtcTimeFieldsValid (
  IN EFI_TIME *Time
  )
{
  if (Time->Year < PcdGet16 (PcdMinimalValidYear) ||
      Time->Year > PcdGet16 (PcdMaximalValidYear) ||
      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))) != 0)) {
    return EFI_INVALID_PARAMETER;
  }

  return EFI_SUCCESS;
}

/**
  See if field Day of an EFI_TIME is correct.

  @param    Time   Its Day field is to be checked.

  @retval   TRUE   Day field of Time is correct.
  @retval   FALSE  Day field of Time is NOT correct.
**/
BOOLEAN
DayValid (
  IN  EFI_TIME  *Time
  )
{
  //
  // The validity of Time->Month field should be checked before
  //
  ASSERT (Time->Month >=1);
  ASSERT (Time->Month <=12);
  if (Time->Day < 1 ||
      Time->Day > mDayOfMonth[Time->Month - 1] ||
      (Time->Month == 2 && (!IsLeapYear (Time) && Time->Day > 28))
      ) {
    return FALSE;
  }

  return TRUE;
}

/**
  Check if it is a leap year.

  @param    Time   The time to be checked.

  @retval   TRUE   It is a leap year.
  @retval   FALSE  It is NOT a leap year.
**/
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;
  }
}

/**
  Converts time from EFI_TIME format defined by UEFI spec to RTC's.

  This function converts time from EFI_TIME format defined by UEFI spec to RTC's.
  If data mode of RTC is BCD, then converts EFI_TIME to it.
  If RTC is in 12-hour format, then converts EFI_TIME to it.

  @param   Time       On input, the time data read from UEFI to convert
                      On output, the time converted to RTC format
  @param   RegisterB  Value of Register B of RTC, indicating data mode
**/
VOID
ConvertEfiTimeToRtcTime (
  IN OUT EFI_TIME        *Time,
  IN     RTC_REGISTER_B  RegisterB
  )
{
  BOOLEAN IsPM;

  IsPM = TRUE;
  //
  // Adjust hour field if RTC is in 12 hour mode
  //
  if (RegisterB.Bits.Mil == 0) {
    if (Time->Hour < 12) {
      IsPM = FALSE;
    }

    if (Time->Hour >= 13) {
      Time->Hour = (UINT8) (Time->Hour - 12);
    } else if (Time->Hour == 0) {
      Time->Hour = 12;
    }
  }
  //
  // Set the Time/Date values.
  //
  Time->Year  = (UINT16) (Time->Year % 100);

  if (RegisterB.Bits.Dm == 0) {
    Time->Year    = DecimalToBcd8 ((UINT8) Time->Year);
    Time->Month   = DecimalToBcd8 (Time->Month);
    Time->Day     = DecimalToBcd8 (Time->Day);
    Time->Hour    = DecimalToBcd8 (Time->Hour);
    Time->Minute  = DecimalToBcd8 (Time->Minute);
    Time->Second  = DecimalToBcd8 (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 && IsPM) {
    Time->Hour = (UINT8) (Time->Hour | 0x80);
  }
}

/**
  Compare the Hour, Minute and Second of the From time and the To time.
  
  Only compare H/M/S in EFI_TIME and ignore other fields here.

  @param From   the first time
  @param To     the second time

  @return  >0   The H/M/S of the From time is later than those of To time
  @return  ==0  The H/M/S of the From time is same as those of To time
  @return  <0   The H/M/S of the From time is earlier than those of To time
**/
INTN
CompareHMS (
  IN EFI_TIME   *From,
  IN EFI_TIME   *To
  )
{
  if ((From->Hour > To->Hour) ||
     ((From->Hour == To->Hour) && (From->Minute > To->Minute)) ||
     ((From->Hour == To->Hour) && (From->Minute == To->Minute) && (From->Second > To->Second))) {
    return 1;
  } else if ((From->Hour == To->Hour) && (From->Minute == To->Minute) && (From->Second == To->Second)) {
    return 0;
  } else {
    return -1;
  }
}

/**
  To check if second date is later than first date within 24 hours.

  @param  From   the first date
  @param  To     the second date

  @retval TRUE   From is previous to To within 24 hours.
  @retval FALSE  From is later, or it is previous to To more than 24 hours.
**/
BOOLEAN
IsWithinOneDay (
  IN EFI_TIME  *From,
  IN EFI_TIME  *To
  )
{
  BOOLEAN Adjacent;

  Adjacent = FALSE;

  //
  // The validity of From->Month field should be checked before
  //
  ASSERT (From->Month >=1);
  ASSERT (From->Month <=12);
  
  if (From->Year == To->Year) {
    if (From->Month == To->Month) {
      if ((From->Day + 1) == To->Day) {
        if ((CompareHMS(From, To) >= 0)) {
          Adjacent = TRUE;
        }
      } else if (From->Day == To->Day) {
        if ((CompareHMS(From, To) <= 0)) {
          Adjacent = TRUE;
        }
      }
    } else if (((From->Month + 1) == To->Month) && (To->Day == 1)) {
      if ((From->Month == 2) && !IsLeapYear(From)) {
        if (From->Day == 28) {
          if ((CompareHMS(From, To) >= 0)) {
            Adjacent = TRUE;
          }
        }
      } else if (From->Day == mDayOfMonth[From->Month - 1]) {
        if ((CompareHMS(From, To) >= 0)) {
           Adjacent = TRUE;
        }
      }
    }
  } else if (((From->Year + 1) == To->Year) &&
             (From->Month == 12) &&
             (From->Day   == 31) &&
             (To->Month   == 1)  &&
             (To->Day     == 1)) {
    if ((CompareHMS(From, To) >= 0)) {
      Adjacent = TRUE;
    }
  }

  return Adjacent;
}

/**
  This function find ACPI table with the specified signature in RSDT or XSDT.

  @param Sdt              ACPI RSDT or XSDT.
  @param Signature        ACPI table signature.
  @param TablePointerSize Size of table pointer: 4 or 8.

  @return ACPI table or NULL if not found.
**/
VOID *
ScanTableInSDT (
  IN EFI_ACPI_DESCRIPTION_HEADER    *Sdt,
  IN UINT32                         Signature,
  IN UINTN                          TablePointerSize
  )
{
  UINTN                          Index;
  UINTN                          EntryCount;
  UINTN                          EntryBase;
  EFI_ACPI_DESCRIPTION_HEADER    *Table;

  EntryCount = (Sdt->Length - sizeof (EFI_ACPI_DESCRIPTION_HEADER)) / TablePointerSize;

  EntryBase = (UINTN) (Sdt + 1);
  for (Index = 0; Index < EntryCount; Index++) {
    //
    // When TablePointerSize is 4 while sizeof (VOID *) is 8, make sure the upper 4 bytes are zero.
    //
    Table = 0;
    CopyMem (&Table, (VOID *) (EntryBase + Index * TablePointerSize), TablePointerSize);
    if (Table->Signature == Signature) {
      return Table;
    }
  }

  return NULL;
}

/**
  Notification function of ACPI Table change.

  This is a notification function registered on ACPI Table change event.
  It saves the Century address stored in ACPI FADT table.

  @param  Event        Event whose notification function is being invoked.
  @param  Context      Pointer to the notification function's context.

**/
VOID
EFIAPI
PcRtcAcpiTableChangeCallback (
  IN EFI_EVENT        Event,
  IN VOID             *Context
  )
{
  EFI_STATUS                                    Status;
  EFI_ACPI_2_0_ROOT_SYSTEM_DESCRIPTION_POINTER  *Rsdp;
  EFI_ACPI_DESCRIPTION_HEADER                   *Rsdt;
  EFI_ACPI_DESCRIPTION_HEADER                   *Xsdt;
  EFI_ACPI_2_0_FIXED_ACPI_DESCRIPTION_TABLE     *Fadt;
  EFI_TIME                                      Time;
  UINT8                                         Century;

  Status = EfiGetSystemConfigurationTable (&gEfiAcpiTableGuid, (VOID **) &Rsdp);
  if (EFI_ERROR (Status)) {
    Status = EfiGetSystemConfigurationTable (&gEfiAcpi10TableGuid, (VOID **) &Rsdp);
  }

  if (EFI_ERROR (Status)) {
    return;
  }

  ASSERT (Rsdp != NULL);

  //
  // Find FADT in XSDT
  //
  Fadt = NULL;
  if (Rsdp->Revision >= EFI_ACPI_2_0_ROOT_SYSTEM_DESCRIPTION_POINTER_REVISION) {
    Xsdt = (EFI_ACPI_DESCRIPTION_HEADER *) (UINTN) Rsdp->XsdtAddress;
    Fadt = ScanTableInSDT (Xsdt, EFI_ACPI_2_0_FIXED_ACPI_DESCRIPTION_TABLE_SIGNATURE, sizeof (UINT64));
  }

  if (Fadt == NULL) {
    //
    // Find FADT in RSDT
    //
    Rsdt = (EFI_ACPI_DESCRIPTION_HEADER *) (UINTN) Rsdp->RsdtAddress;
    Fadt = ScanTableInSDT (Rsdt, EFI_ACPI_2_0_FIXED_ACPI_DESCRIPTION_TABLE_SIGNATURE, sizeof (UINT32));
  }

  if ((Fadt != NULL) &&
      (Fadt->Century > RTC_ADDRESS_REGISTER_D) && (Fadt->Century < 0x80) &&
      (mModuleGlobal.CenturyRtcAddress != Fadt->Century)
      ) {
    mModuleGlobal.CenturyRtcAddress = Fadt->Century;
    Status = PcRtcGetTime (&Time, NULL, &mModuleGlobal);
    if (!EFI_ERROR (Status)) {
      Century = (UINT8) (Time.Year / 100);
      Century = DecimalToBcd8 (Century);
      DEBUG ((EFI_D_INFO, "PcRtc: Write 0x%x to CMOS location 0x%x\n", Century, mModuleGlobal.CenturyRtcAddress));
      RtcWrite (mModuleGlobal.CenturyRtcAddress, Century);
    }
  }
}