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