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83d1ffb9 LG |
1 | /** @file\r |
2 | ACPI Timer implements one instance of Timer Library.\r | |
3 | \r | |
5a702acd | 4 | Copyright (c) 2013 - 2018, Intel Corporation. All rights reserved.<BR>\r |
e1d302e5 | 5 | SPDX-License-Identifier: BSD-2-Clause-Patent\r |
83d1ffb9 LG |
6 | \r |
7 | **/\r | |
8 | \r | |
9 | #include <Base.h>\r | |
10 | #include <Library/TimerLib.h>\r | |
11 | #include <Library/BaseLib.h>\r | |
12 | \r | |
62b8b5be SZ |
13 | /**\r |
14 | Calculate TSC frequency.\r | |
15 | \r | |
16 | The TSC counting frequency is determined by comparing how far it counts\r | |
a012df5e SZ |
17 | during a 101.4 us period as determined by the ACPI timer.\r |
18 | The ACPI timer is used because it counts at a known frequency.\r | |
19 | The TSC is sampled, followed by waiting 363 counts of the ACPI timer,\r | |
20 | or 101.4 us. The TSC is then sampled again. The difference multiplied by\r | |
21 | 9861 is the TSC frequency. There will be a small error because of the\r | |
22 | overhead of reading the ACPI timer. An attempt is made to determine and\r | |
23 | compensate for this error.\r | |
62b8b5be SZ |
24 | \r |
25 | @return The number of TSC counts per second.\r | |
26 | \r | |
27 | **/\r | |
28 | UINT64\r | |
29 | InternalCalculateTscFrequency (\r | |
30 | VOID\r | |
31 | );\r | |
32 | \r | |
83d1ffb9 LG |
33 | /**\r |
34 | Internal function to retrieves the 64-bit frequency in Hz.\r | |
35 | \r | |
36 | Internal function to retrieves the 64-bit frequency in Hz.\r | |
37 | \r | |
38 | @return The frequency in Hz.\r | |
39 | \r | |
40 | **/\r | |
41 | UINT64\r | |
42 | InternalGetPerformanceCounterFrequency (\r | |
43 | VOID\r | |
5a702acd | 44 | )\r |
83d1ffb9 | 45 | {\r |
62b8b5be | 46 | return InternalCalculateTscFrequency ();\r |
83d1ffb9 | 47 | }\r |