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210

Revision 3.1

Instruction Set (Continued)

9.2.2

Extended CPUID Levels

Testing for extended CPUID instruction support can be

accomplished by executing a CPUID instruction with the

EAX register initialized to 80000000h. If a value greater

than or equal to 80000000h is returned to the EAX regis-

ter by the CPUID instruction, the processor supports

extended CPUID levels.

9.2.2.1

CPUID Instruction with

EAX = 8000000h

Extended function 80000000h (EAX = 80000000h) of the

CPUID instruction returns the maximum extended CPUID

levels supported by the current processor in EAX (Table 9-

21). The EBX, ECX, and EDX registers are currently

reserved.

9.2.2.2

CPUID Instruction with

EAX = 8000 0001h

Extended function 80000001h (EAX = 80000001h) of the

CPUID instruction returns the processor type, family,

model, and stepping information of the current processor

in EAX. The EBX and ECX registers are reserved.

The extended feature flags supported are returned in the

EDX register as shown in Table 9-23. Each flag refers to a

specific feature and indicates if that feature is present on

the processor. Some of these features have protection

control in CR4. Before using any of these features on the

processor, the software should check the corresponding

feature flag.

Table 9-21. Maximum Extended CPUID Level

Returned

Contents

Description

EAX

80000005h

Maximum Extended CPUID

Level (six levels)

EBX

Reserved

ECX

Reserved

EDX

Reserved

Table 9-22. EAX, EBX, ECX CPUID Data

Returned when EAX = 80000001h

Returned

Contents

Description

EAX[3:0]

Stepping ID

EAX[7:4]

Model

EAX[11:8]

Family

EAX[15:12]

Processor Type

EAX[31:16]

Reserved

EBX

Reserved

ECX

Reserved

Table 9-23. EDX CPUID Data Returned

when EAX = 80000001h

EDX

Returned

Contents*

Feature Flag

CR4

Bit

EDX[0]

FPU On-Chip

EDX[1]

Virtual Mode Extension

EDX[2]

Debugging Extension

EDX[3]

Page Size Extension

(4 MB)

EDX[4]

Time Stamp Counter

EDX[5]

National Semiconductor

Model-Specific Registers

(via RDMSR / WRMSR

Instructions)

EDX[6]

Reserved

EDX[7]

Machine Check Exception

EDX[8]

CMPXCHG8B Instruction

EDX[9]

Reserved

EDX[10]

Reserved

EDX[11]

SYSCALL / SYSRET

Instruction

EDX[12]

Reserved

EDX[13]

Page Global Enable

EDX[14]

Reserved

EDX[15]

Integer Conditional Move

Instruction

EDX[16]

FPU Conditional Move

Instruction

EDX[22:17]

Reserved

EDX[23]

MMX

EDX[24]

6x86MX Multimedia

Extensions

Note: 0 = Not supported

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