PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c

   1 /** @file
   2   ACPI Timer implements one instance of Timer Library.
   3
   4   Copyright (c) 2013 - 2014, Intel Corporation. All rights reserved.<BR>
   5   This program and the accompanying materials
   6   are licensed and made available under the terms and conditions of the BSD License
   7   which accompanies this distribution.  The full text of the license may be found at
   8   http://opensource.org/licenses/bsd-license.php
   9
  10   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  11   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  12
  13 **/
  14
  15 #include <Base.h>
  16 #include <Library/TimerLib.h>
  17 #include <Library/BaseLib.h>
  18
  19 //
  20 // Cached performance counter frequency
  21 //
  22 UINT64  mPerformanceCounterFrequency = 0;
  23
  24 /**
  25   Internal function to retrieves the 64-bit frequency in Hz.
  26
  27   Internal function to retrieves the 64-bit frequency in Hz.
  28
  29   @return The frequency in Hz.
  30
  31 **/
  32 UINT64
  33 InternalGetPerformanceCounterFrequency (
  34   VOID
  35   )
  36 {
  37   BOOLEAN  InterruptState;
  38   UINT64   Count;
  39
  40   if (mPerformanceCounterFrequency == 0) {
  41     InterruptState = SaveAndDisableInterrupts ();
  42     Count = GetPerformanceCounter ();
  43     MicroSecondDelay (100);
  44     mPerformanceCounterFrequency = MultU64x32 (GetPerformanceCounter () - Count, 10000);
  45     SetInterruptState (InterruptState);
  46   }
  47   return  mPerformanceCounterFrequency;
  48 }