mirror of
https://github.com/CloverHackyColor/CloverBootloader.git
synced 2024-11-24 11:45:27 +01:00
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 ();
|
|
}
|