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AMD Geode™ LX Processors Data Book 629
Instruction Set
33234H
8.2.2 Extended CPUID Levels
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.
8.2.2.1 CPUID Instruction with EAX = 80000000h
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.
8.2.2.2 CPUID Instruction with EAX = 80000001h
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
Table 8-19. CPUID Instruction with EAX = 80000000h
Register
(Note 1)
Note 1. The “Register” column is intentionally out of order.
Returned Contents Description Comment
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
Table 8-20. CPUID Instruction with EAX = 80000001h
Register
Returned
Contents Description Comment
EAX 000005Axh Type/Family/Model/Step
EBX 00000000h Reserved
ECX 00000000h Reserved
EDX C0C0A13Dh Feature Flags
Table 8-18. CPUID Instruction Codes with EAX = 00000000
Register
Reset
Value Description Comment