Intel ® 64 Architecture X2Apic - Intel 2ND GENERATION CORE PROCESSOR FAMILY DESKTOP - DATASHEET VOLUME 1 01-2011 Datasheet

Technologies
®
3.7 Intel
The x2APIC architecture extends the xAPIC architecture that provides a key mechanism
for interrupt delivery. This extension is intended primarily to increase processor
addressability.
Specifically, x2APIC:
• Retains all key elements of compatibility to the xAPIC architecture
— delivery modes
— interrupt and processor priorities
— interrupt sources
— interrupt destination types
• Provides extensions to scale processor addressability for both the logical and
physical destination modes
• Adds new features to enhance performance of interrupt delivery
• Reduces complexity of logical destination mode interrupt delivery on link based
architectures
The key enhancements provided by the x2APIC architecture over xAPIC are the
following:
• Support for two modes of operation to provide backward compatibility and
extensibility for future platform innovations
— In xAPIC compatibility mode, APIC registers are accessed through a memory
mapped interface to a 4 KB page, identical to the xAPIC architecture.
— In x2APIC mode, APIC registers are accessed through Model Specific Register
(MSR) interfaces. In this mode, the x2APIC architecture provides significantly
increased processor addressability and some enhancements on interrupt
delivery.
• Increased range of processor addressability in x2APIC mode
— Physical xAPIC ID field increases from 8 bits to 32 bits, allowing for interrupt
processor addressability up to 4G-1 processors in physical destination mode. A
processor implementation of x2APIC architecture can support fewer than 32-
bits in a software transparent fashion.
— Logical xAPIC ID field increases from 8 bits to 32 bits. The 32-bit logical x2APIC
ID is partitioned into two sub-fields—a 16-bit cluster ID and a 16-bit logical ID
within the cluster. Consequently, ((2^20) -16) processors can be addressed in
logical destination mode. Processor implementations can support fewer than
16 bits in the cluster ID sub-field and logical ID sub-field in a software agnostic
fashion.
• More efficient MSR interface to access APIC registers
— To enhance inter-processor and self directed interrupt delivery as well as the
ability to virtualize the local APIC, the APIC register set can be accessed only
through MSR based interfaces in the x2APIC mode. The Memory Mapped IO
(MMIO) interface used by xAPIC is not supported in the x2APIC mode.
• The semantics for accessing APIC registers have been revised to simplify the
programming of frequently-used APIC registers by system software. Specifically,
the software semantics for using the Interrupt Command Register (ICR) and End Of
Interrupt (EOI) registers have been modified to allow for more efficient delivery
and dispatching of interrupts.
Datasheet, Volume 1
64 Architecture x2APIC
41