projects / mirror_edk2.git / blame
| Commit | Line | Data |
|---|---|---|
| 83d1ffb9 LG |
1 | /** @file\r |
| 2 | ACPI Timer implements one instance of Timer Library.\r | |
| 3 | \r | |
| 62b8b5be | 4 | Copyright (c) 2013 - 2016, Intel Corporation. All rights reserved.<BR>\r |
| 83d1ffb9 LG |
5 | This program and the accompanying materials\r |
| 6 | are licensed and made available under the terms and conditions of the BSD License\r | |
| 7 | which accompanies this distribution. The full text of the license may be found at\r | |
| 8 | http://opensource.org/licenses/bsd-license.php\r | |
| 9 | \r | |
| 10 | THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r | |
| 11 | WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r | |
| 12 | \r | |
| 13 | **/\r | |
| 14 | \r | |
| 15 | #include <Base.h>\r | |
| 16 | #include <Library/TimerLib.h>\r | |
| 17 | #include <Library/BaseLib.h>\r | |
| 18 | \r | |
| 62b8b5be SZ |
19 | /**\r |
| 20 | Calculate TSC frequency.\r | |
| 21 | \r | |
| 22 | The TSC counting frequency is determined by comparing how far it counts\r | |
| 23 | during a 100us period as determined by the ACPI timer. The ACPI timer is\r | |
| 24 | used because it counts at a known frequency.\r | |
| 25 | The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000\r | |
| 26 | clocks of the ACPI timer, or 100us. The TSC is then sampled again. The\r | |
| 27 | difference multiplied by 10000 is the TSC frequency. There will be a small\r | |
| 28 | error because of the overhead of reading the ACPI timer. An attempt is\r | |
| 29 | made to determine and compensate for this error.\r | |
| 30 | \r | |
| 31 | @return The number of TSC counts per second.\r | |
| 32 | \r | |
| 33 | **/\r | |
| 34 | UINT64\r | |
| 35 | InternalCalculateTscFrequency (\r | |
| 36 | VOID\r | |
| 37 | );\r | |
| 38 | \r | |
| 83d1ffb9 LG |
39 | //\r |
| 40 | // Cached performance counter frequency\r | |
| 41 | //\r | |
| 42 | UINT64 mPerformanceCounterFrequency = 0;\r | |
| 43 | \r | |
| 44 | /**\r | |
| 45 | Internal function to retrieves the 64-bit frequency in Hz.\r | |
| 46 | \r | |
| 47 | Internal function to retrieves the 64-bit frequency in Hz.\r | |
| 48 | \r | |
| 49 | @return The frequency in Hz.\r | |
| 50 | \r | |
| 51 | **/\r | |
| 52 | UINT64\r | |
| 53 | InternalGetPerformanceCounterFrequency (\r | |
| 54 | VOID\r | |
| 55 | ) \r | |
| 56 | {\r | |
| 83d1ffb9 | 57 | if (mPerformanceCounterFrequency == 0) {\r |
| 62b8b5be | 58 | mPerformanceCounterFrequency = InternalCalculateTscFrequency ();\r |
| 83d1ffb9 LG |
59 | }\r |
| 60 | return mPerformanceCounterFrequency;\r | |
| 61 | }\r |