/** @file | |
A Pei Timer Library implementation which uses the Time Stamp Counter in the processor. | |
For Pentium 4 processors, Intel Xeon processors (family [0FH], models [03H and higher]); | |
for Intel Core Solo and Intel Core Duo processors (family [06H], model [0EH]); | |
for the Intel Xeon processor 5100 series and Intel Core 2 Duo processors (family [06H], model [0FH]); | |
for Intel Core 2 and Intel Xeon processors (family [06H], display_model [17H]); | |
for Intel Atom processors (family [06H], display_model [1CH]): | |
the time-stamp counter increments at a constant rate. | |
That rate may be set by the maximum core-clock to bus-clock ratio of the processor or may be set by | |
the maximum resolved frequency at which the processor is booted. The maximum resolved frequency may | |
differ from the maximum qualified frequency of the processor. | |
The specific processor configuration determines the behavior. Constant TSC behavior ensures that the | |
duration of each clock tick is uniform and supports the use of the TSC as a wall clock timer even if | |
the processor core changes frequency. This is the architectural behavior moving forward. | |
A Processor's support for invariant TSC is indicated by CPUID.0x80000007.EDX[8]. | |
Copyright (c) 2009 - 2011, 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 <PiPei.h> | |
#include <Library/HobLib.h> | |
#include <Guid/TscFrequency.h> | |
#include "TscTimerLibInternal.h" | |
/** Get TSC frequency from TSC frequency GUID HOB, if the HOB is not found, build it. | |
@return The number of TSC counts per second. | |
**/ | |
UINT64 | |
InternalGetTscFrequency ( | |
VOID | |
) | |
{ | |
EFI_HOB_GUID_TYPE *GuidHob; | |
VOID *DataInHob; | |
UINT64 TscFrequency; | |
// | |
// Get TSC frequency from TSC frequency GUID HOB. | |
// | |
GuidHob = GetFirstGuidHob (&gEfiTscFrequencyGuid); | |
if (GuidHob != NULL) { | |
DataInHob = GET_GUID_HOB_DATA (GuidHob); | |
TscFrequency = * (UINT64 *) DataInHob; | |
return TscFrequency; | |
} | |
// | |
// TSC frequency GUID HOB is not found, build it. | |
// | |
TscFrequency = InternalCalculateTscFrequency (); | |
// | |
// TscFrequency is now equal to the number of TSC counts per second, build GUID HOB for it. | |
// | |
BuildGuidDataHob ( | |
&gEfiTscFrequencyGuid, | |
&TscFrequency, | |
sizeof (UINT64) | |
); | |
return TscFrequency; | |
} | |