PcAtChipsetPkg/Library/AcpiTimerLib/DxeStandaloneMmAcpiTimerLib.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   SPDX-License-Identifier: BSD-2-Clause-Patent
   6
   7 **/
   8
   9 #include <PiDxe.h>
  10 #include <Library/TimerLib.h>
  11 #include <Library/BaseLib.h>
  12 #include <Library/HobLib.h>
  13
  14 extern GUID  mFrequencyHobGuid;
  15
  16 /**
  17   The constructor function enables ACPI IO space.
  18
  19   If ACPI I/O space not enabled, this function will enable it.
  20   It will always return RETURN_SUCCESS.
  21
  22   @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.
  23
  24 **/
  25 RETURN_STATUS
  26 EFIAPI
  27 AcpiTimerLibConstructor (
  28   VOID
  29   );
  30
  31 /**
  32   Calculate TSC frequency.
  33
  34   The TSC counting frequency is determined by comparing how far it counts
  35   during a 101.4 us period as determined by the ACPI timer.
  36   The ACPI timer is used because it counts at a known frequency.
  37   The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
  38   or 101.4 us. The TSC is then sampled again. The difference multiplied by
  39   9861 is the TSC frequency. There will be a small error because of the
  40   overhead of reading the ACPI timer. An attempt is made to determine and
  41   compensate for this error.
  42
  43   @return The number of TSC counts per second.
  44
  45 **/
  46 UINT64
  47 InternalCalculateTscFrequency (
  48   VOID
  49   );
  50
  51 //
  52 // Cached performance counter frequency
  53 //
  54 UINT64  mPerformanceCounterFrequency = 0;
  55
  56 /**
  57   Internal function to retrieves the 64-bit frequency in Hz.
  58
  59   Internal function to retrieves the 64-bit frequency in Hz.
  60
  61   @return The frequency in Hz.
  62
  63 **/
  64 UINT64
  65 InternalGetPerformanceCounterFrequency (
  66   VOID
  67   )
  68 {
  69   return mPerformanceCounterFrequency;
  70 }
  71
  72 /**
  73   The constructor function enables ACPI IO space, and caches PerformanceCounterFrequency.
  74
  75   @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.
  76
  77 **/
  78 EFI_STATUS
  79 CommonAcpiTimerLibConstructor (
  80   VOID
  81   )
  82 {
  83   EFI_HOB_GUID_TYPE  *GuidHob;
  84
  85   //
  86   // Enable ACPI IO space.
  87   //
  88   AcpiTimerLibConstructor ();
  89
  90   //
  91   // Initialize PerformanceCounterFrequency
  92   //
  93   GuidHob = GetFirstGuidHob (&mFrequencyHobGuid);
  94   if (GuidHob != NULL) {
  95     mPerformanceCounterFrequency = *(UINT64 *)GET_GUID_HOB_DATA (GuidHob);
  96   } else {
  97     mPerformanceCounterFrequency = InternalCalculateTscFrequency ();
  98   }
  99
 100   return EFI_SUCCESS;
 101 }