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Appendix A
Embedded AMD-K6™ Processors BIOS Design Guide
23913A/0—November 2000
Preliminary Information
Standard Functions
Function 0 — Largest Standard Function Input Value and Vendor Identification String
Input:
EAX = 0
Output:
EAX = Largest function input value recognized by the CPUID instruction
EBX, EDX, ECX = Vendor identification string
This is a standard function found in all processors implementing the CPUID
instruction. It returns two values. The first value is returned in the EAX register and
indicates the largest standard function value recognized by the processor. The second
value is the vendor identification string. This 12-character ASCII string is returned in
the EBX, EDX, and ECX registers in little-endian format. AMD processors return a
vendor identification string of “AuthenticAMD” as follows:
Software uses the vendor identification string as follows:
■
To identify the processor as an AMD processor
■
To apply AMD’s definition of the CPUID instruction for all additional function
calls
Function 1 — Processor Signature and Standard Feature Flags
Input:
EAX = 1
Output:
EAX = Processor Signature
EBX = Reserved
ECX = Reserved
EDX = Standard Feature Flags
Function 1 returns two values — the Processor Signature and the Standard Feature
Flags. The processor signature is returned in the EAX register and identifies the
specific processor by providing information on its type — instruction family, model,
and revision (stepping). The information is formatted as follows:
■
EAX[3–0]
Stepping ID
■
EAX[7–4]
Model
■
EAX[11–8]
Instruction Family
■
EAX[31–12]
Reserved
EBX
EDX
ECX
h
t
u
A
i
t
n
e
D
M
A
c
68
74
75
41
69
74
6E
65
44
4D
41
63