AMD AMD5K86 - CPUID

AMD~
18524B/O-Mar1996 AMD5J!36 Processor Technical Reference Manual
3.3.1 CPUID
mnemonic
CPUID
Privilege:
Registers Affected:
Flags Affected:
Exceptions Generated:
opcode description
OFA2h Identify processor
CPL=O
EAX,EBX, ECX, EDX
none
Real, Virtual-8086 mode-none
Protected mode-none
The CPUID instruction identifies the type of processor and the features it supports.
A 0 or 1 value written to the EAX register specifies what information will be
returned by the instruction.
The processor implements the ID flag (bit 21) in the EFLAGS register. By writing and
reading this bit, software can verify that the processor will execute the CPUID
instruction.
If 0 is written to EAX, the following values are returned in EAX, EBX, ECX, and
EDX:
• EAX:00000001h
• EBX: 68747541h
• ECX: 444D4163h
• EDX: 69746E65h
These values decode to the ASCII string "AuthenticAMD" when read in the EBX-
EDX-ECX
registers in least significant byte to most significant byte order.
If 1 is written to EAX, the following value is returned in the bit locations of EAX and
EDX:
• EAX:
• EAX[3-0]
• EAX[7-4]
• EAX[11-8]
• EAX[31-12]
New Instructions
Stepping ID
Model:
AMD-SSA5 processor (O,OOOOb)
AMD5
K
86 processor (l,OOOlb)
Family (0101b)
reserved
3-29