diff options
Diffstat (limited to 'Core/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c')
-rw-r--r-- | Core/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/Core/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c b/Core/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c new file mode 100644 index 0000000000..b141c680fb --- /dev/null +++ b/Core/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c @@ -0,0 +1,61 @@ +/** @file
+ ACPI Timer implements one instance of Timer Library.
+
+ Copyright (c) 2013 - 2016, Intel Corporation. All rights reserved.<BR>
+ This program and the accompanying materials
+ are licensed and made available under the terms and conditions of the BSD License
+ which accompanies this distribution. The full text of the license may be found at
+ http://opensource.org/licenses/bsd-license.php
+
+ THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+
+#include <Base.h>
+#include <Library/TimerLib.h>
+#include <Library/BaseLib.h>
+
+/**
+ Calculate TSC frequency.
+
+ The TSC counting frequency is determined by comparing how far it counts
+ during a 101.4 us period as determined by the ACPI timer.
+ The ACPI timer is used because it counts at a known frequency.
+ The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
+ or 101.4 us. The TSC is then sampled again. The difference multiplied by
+ 9861 is the TSC frequency. There will be a small error because of the
+ overhead of reading the ACPI timer. An attempt is made to determine and
+ compensate for this error.
+
+ @return The number of TSC counts per second.
+
+**/
+UINT64
+InternalCalculateTscFrequency (
+ VOID
+ );
+
+//
+// Cached performance counter frequency
+//
+UINT64 mPerformanceCounterFrequency = 0;
+
+/**
+ Internal function to retrieves the 64-bit frequency in Hz.
+
+ Internal function to retrieves the 64-bit frequency in Hz.
+
+ @return The frequency in Hz.
+
+**/
+UINT64
+InternalGetPerformanceCounterFrequency (
+ VOID
+ )
+{
+ if (mPerformanceCounterFrequency == 0) {
+ mPerformanceCounterFrequency = InternalCalculateTscFrequency ();
+ }
+ return mPerformanceCounterFrequency;
+}
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