+/** @file\r
+ ACPI Timer implements one instance of Timer Library.\r
+\r
+ Copyright (c) 2013 - 2018, Intel Corporation. All rights reserved.<BR>\r
+ This program and the accompanying materials\r
+ are licensed and made available under the terms and conditions of the BSD License\r
+ which accompanies this distribution. The full text of the license may be found at\r
+ http://opensource.org/licenses/bsd-license.php\r
+\r
+ THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
+ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
+\r
+**/\r
+\r
+#include <PiPei.h>\r
+#include <Library/TimerLib.h>\r
+#include <Library/BaseLib.h>\r
+#include <Library/HobLib.h>\r
+\r
+extern GUID mFrequencyHobGuid;\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
+ UINT64 *PerformanceCounterFrequency;\r
+ EFI_HOB_GUID_TYPE *GuidHob;\r
+\r
+ PerformanceCounterFrequency = NULL;\r
+ GuidHob = GetFirstGuidHob (&mFrequencyHobGuid);\r
+ if (GuidHob == NULL) {\r
+ PerformanceCounterFrequency = (UINT64*)BuildGuidHob(&mFrequencyHobGuid, sizeof (*PerformanceCounterFrequency));\r
+ ASSERT (PerformanceCounterFrequency != NULL);\r
+ *PerformanceCounterFrequency = InternalCalculateTscFrequency ();\r
+ } else {\r
+ PerformanceCounterFrequency = (UINT64*)GET_GUID_HOB_DATA (GuidHob);\r
+ }\r
+\r
+ return *PerformanceCounterFrequency;\r
+}\r