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Last change
on this file since 107064 was 80721, checked in by vboxsync, 5 years ago |
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Devices/EFI/FirmwareNew: Start upgrade process to edk2-stable201908 (compiles on Windows and works to some extent), bugref:4643
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Property svn:eol-style
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File size:
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| 1 | /** @file
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| 2 | ACPI Timer implements one instance of Timer Library.
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| 3 |
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| 4 | Copyright (c) 2013 - 2018, Intel Corporation. All rights reserved.<BR>
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| 5 | SPDX-License-Identifier: BSD-2-Clause-Patent
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| 6 |
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| 7 | **/
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| 8 |
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| 9 | #include <Base.h>
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| 10 | #include <Library/TimerLib.h>
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| 11 | #include <Library/BaseLib.h>
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| 12 |
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| 13 | /**
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| 14 | Calculate TSC frequency.
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| 15 |
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| 16 | The TSC counting frequency is determined by comparing how far it counts
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| 17 | during a 101.4 us period as determined by the ACPI timer.
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| 18 | The ACPI timer is used because it counts at a known frequency.
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| 19 | The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
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| 20 | or 101.4 us. The TSC is then sampled again. The difference multiplied by
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| 21 | 9861 is the TSC frequency. There will be a small error because of the
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| 22 | overhead of reading the ACPI timer. An attempt is made to determine and
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| 23 | compensate for this error.
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| 24 |
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| 25 | @return The number of TSC counts per second.
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| 26 |
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| 27 | **/
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| 28 | UINT64
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| 29 | InternalCalculateTscFrequency (
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| 30 | VOID
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| 31 | );
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| 32 |
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| 33 | /**
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| 34 | Internal function to retrieves the 64-bit frequency in Hz.
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| 35 |
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| 36 | Internal function to retrieves the 64-bit frequency in Hz.
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| 37 |
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| 38 | @return The frequency in Hz.
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| 39 |
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| 40 | **/
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| 41 | UINT64
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| 42 | InternalGetPerformanceCounterFrequency (
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| 43 | VOID
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| 44 | )
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| 45 | {
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| 46 | return InternalCalculateTscFrequency ();
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| 47 | }
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