MdeModulePkg/Core/Dxe/Misc/Stall.c

/** @file
  UEFI Miscellaneous boot Services Stall service implementation

Copyright (c) 2006 - 2017, 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 statements
//

#include "DxeMain.h"

/**
  Internal worker function to call the Metronome Architectural Protocol for 
  the number of ticks specified by the UINT64 Counter value.  WaitForTick() 
  service of the Metronome Architectural Protocol uses a UINT32 for the number
  of ticks to wait, so this function loops when Counter is larger than 0xffffffff.

  @param  Counter           Number of ticks to wait.

**/
VOID
CoreInternalWaitForTick (
  IN UINT64  Counter
  )
{
  while (RShiftU64 (Counter, 32) > 0) {
    gMetronome->WaitForTick (gMetronome, 0xffffffff);
    Counter -= 0xffffffff;
  }
  gMetronome->WaitForTick (gMetronome, (UINT32)Counter);
}

/**
  Introduces a fine-grained stall.

  @param  Microseconds           The number of microseconds to stall execution.

  @retval EFI_SUCCESS            Execution was stalled for at least the requested
                                 amount of microseconds.
  @retval EFI_NOT_AVAILABLE_YET  gMetronome is not available yet

**/
EFI_STATUS
EFIAPI
CoreStall (
  IN UINTN            Microseconds
  )
{
  UINT64  Counter;
  UINT32  Remainder;
  UINTN   Index;

  if (gMetronome == NULL) {
    return EFI_NOT_AVAILABLE_YET;
  }

  //
  // Counter = Microseconds * 10 / gMetronome->TickPeriod
  // 0x1999999999999999 = (2^64 - 1) / 10
  //
  if ((UINT64) Microseconds > 0x1999999999999999ULL) {
    //
    // Microseconds is too large to multiple by 10 first.  Perform the divide 
    // operation first and loop 10 times to avoid 64-bit math overflow.
    //
    Counter = DivU64x32Remainder (
                Microseconds,
                gMetronome->TickPeriod,
                &Remainder
                );
    for (Index = 0; Index < 10; Index++) {
      CoreInternalWaitForTick (Counter);
    }      

    if (Remainder != 0) {
      //
      // If Remainder was not zero, then normally, Counter would be rounded 
      // up by 1 tick.  In this case, since a loop for 10 counts was used
      // to emulate the multiply by 10 operation, Counter needs to be rounded
      // up by 10 counts.
      //
      CoreInternalWaitForTick (10);
    }
  } else {
    //
    // Calculate the number of ticks by dividing the number of microseconds by
    // the TickPeriod.  Calculation is based on 100ns unit.
    //
    Counter = DivU64x32Remainder (
                MultU64x32 (Microseconds, 10),
                gMetronome->TickPeriod,
                &Remainder
                );
    if (Remainder != 0) {
      //
      // If Remainder is not zero, then round Counter up by one tick.
      //
      Counter++;
    }
    CoreInternalWaitForTick (Counter);
  }

  return EFI_SUCCESS;
}