PcAtChipsetPkg: Clean up source files

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

diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
index 21fdb79908b89baedc235c283f6ea63bcf45e29f..2d79c6c1f1ff9ffe2980d7969df39cfde6493458 100644 (file)
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
@@ -1,7 +1,7 @@
 /** @file\r
   ACPI Timer implements one instance of Timer Library.\r
 \r
-  Copyright (c) 2013 - 2014, Intel Corporation. All rights reserved.<BR>\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
@@ -16,6 +16,26 @@
 #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
@@ -27,16 +47,7 @@
 UINT64\r
 InternalGetPerformanceCounterFrequency (\r
   VOID\r
-  ) \r
+  )\r
 {\r
-  BOOLEAN  InterruptState;\r
-  UINT64   Count;\r
-  UINT64   Frequency;\r
-  \r
-  InterruptState = SaveAndDisableInterrupts ();\r
-  Count = GetPerformanceCounter ();\r
-  MicroSecondDelay (100);\r
-  Frequency = MultU64x32 (GetPerformanceCounter () - Count, 10000);\r
-  SetInterruptState (InterruptState);\r
-  return Frequency;\r
+  return InternalCalculateTscFrequency ();\r
 }\r