AMD LX 900@1.5W Benutzerhandbuch

33234H

Testing for extended CPUID instruction support can be accomplished by executing a CPUID instruction with the EAX regis-
ter initialized to 80000000h. If a value greater than or equal to 80000000h is returned to the EAX register by the CPUID
instruction, the processor supports extended CPUID levels.

Extended function 80000000h (EAX = 80000000h) of the CPUID instruction returns the maximum extended CPUID sup-
ported levels as well as the processor vendor string.

After the instruction is executed, the EAX register contains the maximum extended CPUID levels supported. The maximum
extended standard CPUID level is the highest acceptable value for the EAX register input.

The EBX through EDX registers contain the vendor string of the processor as shown in Table 8-19.

Extended function 80000001h (EAX = 80000001h) of the CPUID instruction returns the processor type, family, model, step-
ping information in the EAX register, and the supported extended feature flags in the EDX register. The EBX and ECX reg-
isters are reserved. Table 8-20 provides a register map.

In the EDX register, each flag refers to a specific extended feature. Some of these features have protection control in CR4.
Before using any of these extended features, the software should check the corresponding flag. Attempting to execute an
unavailable extended feature can cause exceptions and unexpected behavior. 

Table 8-21 on page 630 shows the EAX and EDX bit field formats when EAX = 80000001h and indicates if a feature is not
supported. 

EDX[1]

0

VME. Virtual Interrupt Flag in VM86

Not supported

EDX[0]

1

FPU. Floating Point Unit On Chip

Note 1. The “Register” column is intentionally out of order.

EAX

80000006h

Maximum Extended CPUID Level

EBX

68747541h 

 {htuA}

Vendor ID String 1

EDX

69746E65h

{itne}

Vendor ID String 2 

ECX

444D4163h

{DMAc}

Vendor ID String 3

EAX

000005Axh

Type/Family/Model/Step  

EBX

00000000h

Reserved

ECX

00000000h

Reserved

EDX

C0C0A13Dh

Feature Flags