PcAtChipsetPkg: Replace BSD License with BSD+Patent License

[mirror_edk2.git] / PcAtChipsetPkg / Library / AcpiTimerLib / BaseAcpiTimerLib.c

/** @file\r
  ACPI Timer implements one instance of Timer Library.\r
\r
  Copyright (c) 2013 - 2018, Intel Corporation. All rights reserved.<BR>\r
  SPDX-License-Identifier: BSD-2-Clause-Patent\r
\r
**/\r
\r
#include <Base.h>\r
#include <Library/TimerLib.h>\r
#include <Library/BaseLib.h>\r
\r
/**\r
  Calculate TSC frequency.\r
\r
  The TSC counting frequency is determined by comparing how far it counts\r
  during a 101.4 us period as determined by the ACPI timer.\r
  The ACPI timer is used because it counts at a known frequency.\r
  The TSC is sampled, followed by waiting 363 counts of the ACPI timer,\r
  or 101.4 us. The TSC is then sampled again. The difference multiplied by\r
  9861 is the TSC frequency. There will be a small error because of the\r
  overhead of reading the ACPI timer. An attempt is made to determine and\r
  compensate for this error.\r
\r
  @return The number of TSC counts per second.\r
\r
**/\r
UINT64\r
InternalCalculateTscFrequency (\r
  VOID\r
  );\r
\r
/**\r
  Internal function to retrieves the 64-bit frequency in Hz.\r
\r
  Internal function to retrieves the 64-bit frequency in Hz.\r
\r
  @return The frequency in Hz.\r
\r
**/\r
UINT64\r
InternalGetPerformanceCounterFrequency (\r
  VOID\r
  )\r
{\r
  return InternalCalculateTscFrequency ();\r
}\r