Specification Update 55
Documentation Changes
The Documentation Changes listed in this section apply to the following documents:
•Intel
® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1: Basic
Architecture
•Intel
® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A:
Instruction Set Reference Manual A-M
•Intel
® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B:
Instruction Set Reference Manual N-Z
•Intel
® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A:
System Programming Guide
•Intel
® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3B:
System Programming Guide
All Documentation Changes will be incorporated into a future version of the appropriate
Processor documentation.
Note: Documentation changes for Intel® 64 and IA-32 Architecture Software Developer's
Manual volumes 1, 2A, 2B, 3A, and 3B will be posted in a separate document, Intel® 64
and IA-32 Architecture Software Developer's Manual Documentation Changes. Follow
the link below to become familiar with this file.
http://developer.intel.com/products/processor/manuals/index.htm
There are no new Documentation Changes in this Specification Update revision.
BU1. On-Demand Clock Modulation Feature Clarification
Software Controlled Clock Modulation section of the Intel® 64 and IA-32 Architectures
Software Developer's Manual, Volume 3B: System Programming Guide will be modified
to differentiate On-demand clock modulation feature on different processors. The
clarification will state:
For Hyper-Threading Technology enabled processors, the IA32_CLOCK_MODULATION
register is duplicated for each logical processor. In order for the On-demand clock
modulation feature to work properly, the feature must be enabled on all the logical
processors within a physical processor. If the programmed duty cycle is not identical for
all the logical processors, the processor clock will modulate to the highest duty cycle
programmed for processors if the CPUID DisplayFamily_DisplayModel signatures is
listed in Table 14-2. For all other processors, if the programmed duty cycle is not
identical for all logical processors in the same core, the processor will modulate at the
lowest programmed duty cycle.
For multiple processor cores in a physical package, each core can modulate to a
programmed duty cycle independently.
For the P6 family processors, on-demand clock modulation was implemented through
the chipset, which controlled clock modulation through the processor’s STPCLK# pin.
Table 14-2. CPUID Signatures for Legacy Processors That Resolve to Higher
Performance Setting of Conflicting Duty Cycle Requests