/** @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 | |
); | |
/** | |
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 (); | |
} |