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Instruction Set (Continued)

8.2

CPUID INSTRUCTION

The CPUID instruction (opcode 0FA2) allows the software

to make processor inquiries as to the vendor, family, model,

stepping, features and also provides cache information.

The GX1 supports both the standard and National Semi-

conductor extended CPUID levels.

The presence of the CPUID instruction is indicated by the

ability to change the value of the ID Flag, bit 21 in the

EFLAGS register.

The CPUID level allows the CPUID instruction to return dif-

ferent information in the EAX, EBX, ECX, aand EDX regis-

ters. The level is determined by the initialized value of the

EAX register before the instruction is executed. A summary

of theCPUID levels is showninTable 8-16.

8.2.1

Standard CPUID Levels

The standard CPUID levels are part of the standard x86

instruction set.

8.2.1.1

CPUID Instruction with EAX = 0000 0000h

Standard function 0h (EAX = 0) of the CPUID instruction

returnsthe maximumstandard CPUIDlevelsaswellasthe

processor vendor string.

After the instruction is executed, the EAX register contains

the maximum standard CPUID levels supported. The maxi-

mum standard CPUID level is the highest acceptable value

for the EAX register input. This does not include the

extended CPUID levels.

The EBX through EDX registers contain the vendor string

of the processor as shown in Table 8-17.

Table 8-16. CPUID Levels Summary

CPUID

Type

Initialized

EAX

Returned Data in EAX, EBX,

ECX, EDX Registers

Standard

00000000h

Maximum standard levels, CPU

vendor string

Standard

00000001h

Model, family, type and features

Standard

00000002h

TLB and cache information

Extended

80000000h

Maximum extended levels

Extended

80000001h

Extended model, family, type and

features

Extended

80000002h

CPU marketing name string

Extended

80000003h

Extended

80000004h

Extended

80000005h

TLB and L1 cache description

Table 8-17. CPUID Data Returned when EAX = 0

Register1

The register column is intentionally out of order.

Returned Contents

Description

EAX

Maximum Standard

Level

EBX

6547

(doeG)

Vendor ID String 1

EDX

2065

(yb e)

Vendor ID String 2

ECX

43534E20

(CSN )

Vendor ID String 3

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