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- /** @file
- ACPI Timer implements one instance of Timer Library.
- Copyright (c) 2013 - 2018, Intel Corporation. All rights reserved.<BR>
- SPDX-License-Identifier: BSD-2-Clause-Patent
- **/
- #include <PiPei.h>
- #include <Library/TimerLib.h>
- #include <Library/BaseLib.h>
- #include <Library/HobLib.h>
- #include <Library/DebugLib.h>
- extern GUID mFrequencyHobGuid;
- /**
- 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
- );
- /**
- 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
- )
- {
- UINT64 *PerformanceCounterFrequency;
- EFI_HOB_GUID_TYPE *GuidHob;
- PerformanceCounterFrequency = NULL;
- GuidHob = GetFirstGuidHob (&mFrequencyHobGuid);
- if (GuidHob == NULL) {
- PerformanceCounterFrequency = (UINT64*)BuildGuidHob(&mFrequencyHobGuid, sizeof (*PerformanceCounterFrequency));
- ASSERT (PerformanceCounterFrequency != NULL);
- *PerformanceCounterFrequency = InternalCalculateTscFrequency ();
- } else {
- PerformanceCounterFrequency = (UINT64*)GET_GUID_HOB_DATA (GuidHob);
- }
- return *PerformanceCounterFrequency;
- }
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