e1d302e554
https://bugzilla.tianocore.org/show_bug.cgi?id=1373 Replace BSD 2-Clause License with BSD+Patent License. This change is based on the following emails: https://lists.01.org/pipermail/edk2-devel/2019-February/036260.html https://lists.01.org/pipermail/edk2-devel/2018-October/030385.html RFCs with detailed process for the license change: V3: https://lists.01.org/pipermail/edk2-devel/2019-March/038116.html V2: https://lists.01.org/pipermail/edk2-devel/2019-March/037669.html V1: https://lists.01.org/pipermail/edk2-devel/2019-March/037500.html Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com> Reviewed-by: Ray Ni <ray.ni@intel.com>
48 lines
1.2 KiB
C
48 lines
1.2 KiB
C
/** @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 <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
|
|
);
|
|
|
|
/**
|
|
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
|
|
)
|
|
{
|
|
return InternalCalculateTscFrequency ();
|
|
}
|