PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c

   1 /** @file
   2   ACPI Timer implements one instance of Timer Library.
   3
   4   Copyright (c) 2013 - 2018, 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 <PiDxe.h>
  16 #include <Library/TimerLib.h>
  17 #include <Library/BaseLib.h>
  18 #include <Library/HobLib.h>
  19
  20 extern GUID mFrequencyHobGuid;
  21
  22 /**
  23   The constructor function enables ACPI IO space.
  24
  25   If ACPI I/O space not enabled, this function will enable it.
  26   It will always return RETURN_SUCCESS.
  27
  28   @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.
  29
  30 **/
  31 RETURN_STATUS
  32 EFIAPI
  33 AcpiTimerLibConstructor (
  34   VOID
  35   );
  36
  37 /**
  38   Calculate TSC frequency.
  39
  40   The TSC counting frequency is determined by comparing how far it counts
  41   during a 101.4 us period as determined by the ACPI timer.
  42   The ACPI timer is used because it counts at a known frequency.
  43   The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
  44   or 101.4 us. The TSC is then sampled again. The difference multiplied by
  45   9861 is the TSC frequency. There will be a small error because of the
  46   overhead of reading the ACPI timer. An attempt is made to determine and
  47   compensate for this error.
  48
  49   @return The number of TSC counts per second.
  50
  51 **/
  52 UINT64
  53 InternalCalculateTscFrequency (
  54   VOID
  55   );
  56
  57 //
  58 // Cached performance counter frequency
  59 //
  60 UINT64  mPerformanceCounterFrequency = 0;
  61
  62 /**
  63   Internal function to retrieves the 64-bit frequency in Hz.
  64
  65   Internal function to retrieves the 64-bit frequency in Hz.
  66
  67   @return The frequency in Hz.
  68
  69 **/
  70 UINT64
  71 InternalGetPerformanceCounterFrequency (
  72   VOID
  73   )
  74 {
  75   return  mPerformanceCounterFrequency;
  76 }
  77
  78 /**
  79   The constructor function enables ACPI IO space, and caches PerformanceCounterFrequency.
  80
  81   @param  ImageHandle   The firmware allocated handle for the EFI image.
  82   @param  SystemTable   A pointer to the EFI System Table.
  83
  84   @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.
  85
  86 **/
  87 EFI_STATUS
  88 EFIAPI
  89 DxeAcpiTimerLibConstructor (
  90   IN EFI_HANDLE        ImageHandle,
  91   IN EFI_SYSTEM_TABLE  *SystemTable
  92   )
  93 {
  94   EFI_HOB_GUID_TYPE   *GuidHob;
  95
  96   //
  97   // Enable ACPI IO space.
  98   //
  99   AcpiTimerLibConstructor ();
 100
 101   //
 102   // Initialize PerformanceCounterFrequency
 103   //
 104   GuidHob = GetFirstGuidHob (&mFrequencyHobGuid);
 105   if (GuidHob != NULL) {
 106     mPerformanceCounterFrequency = *(UINT64*)GET_GUID_HOB_DATA (GuidHob);
 107   } else {
 108     mPerformanceCounterFrequency = InternalCalculateTscFrequency ();
 109   }
 110
 111   return EFI_SUCCESS;
 112 }