PcAtChipsetPkg AcpiTimerLib: Get more accurate TSC Frequency

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

diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
index 6f5c07a4f0b4d6d9a156e885a5aa6e1d0a216ed3..7f7b0f8f62947712e3a3a3d66df51ddeece1c14a 100644 (file)
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.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 - 2016, 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 100us period as determined by the ACPI timer. The ACPI timer is\r
+  used because it counts at a known frequency.\r
+  The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000\r
+  clocks of the ACPI timer, or 100us. The TSC is then sampled again. The\r
+  difference multiplied by 10000 is the TSC frequency. There will be a small\r
+  error because of the overhead of reading the ACPI timer. An attempt is\r
+  made to determine and 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
 // Cached performance counter frequency\r
 //\r
@@ -34,15 +54,8 @@ InternalGetPerformanceCounterFrequency (
   VOID\r
   ) \r
 {\r
-  BOOLEAN  InterruptState;\r
-  UINT64   Count;\r
-\r
   if (mPerformanceCounterFrequency == 0) {\r
-    InterruptState = SaveAndDisableInterrupts ();\r
-    Count = GetPerformanceCounter ();\r
-    MicroSecondDelay (100);\r
-    mPerformanceCounterFrequency = MultU64x32 (GetPerformanceCounter () - Count, 10000);\r
-    SetInterruptState (InterruptState);\r
+    mPerformanceCounterFrequency = InternalCalculateTscFrequency ();\r
   }\r
   return  mPerformanceCounterFrequency;\r
 }\r