Instruction Set (Continued)
8.2.2 Extended CPUID Levels
Table 8-22. EAX, EBX, ECX CPUID Data
Returned when EAX = 80000001h
Testing for extended CPUID instruction support can be
accomplished by executing a CPUID instruction with the
EAX register initialized to 80000000h. If a value greater
than or equal to 8000 0000h is returned to the EAX regis-
ter by the CPUID instruction, the processor supports
extended CPUID levels.
Returned
Register
Contents
Description
Stepping ID
EAX[3:0]
EAX[7:4]
EAX[11:8]
EAX[15:12]
EAX[31:16]
EBX
xx
4
5
0
-
Model
Family
8.2.2.1 CPUID Instruction with EAX = 80000000h
Extended function 8000 0000h (EAX = 80000000h) of the
CPUID instruction returns the maximum extended CPUID
levels supported by the current processor in EAX (Table 8-
21). The EBX, ECX, and EDX registers are currently
reserved.
Processor Type
Reserved
Reserved
Reserved
-
ECX
-
Table 8-23. EDX CPUID Data Returned
when EAX = 80000001h
Table 8-21. Maximum Extended CPUID Level
Returned
Register
Contents
Description
Returned
Contents*
CR4
Bit
EDX
Feature Flag
FPU On-Chip
EAX
80000005h
Maximum Extended CPUID
Level (six levels)
EDX[0]
EDX[1]
EDX[2]
EDX[3]
1
0
0
0
-
-
-
-
EBX
ECX
EDX
-
-
-
Reserved
Reserved
Reserved
Virtual Mode Extension
Debugging Extension
Page Size Extension
(4 MB)
EDX[4]
EDX[5]
1
1
Time Stamp Counter
2
-
8.2.2.2 CPUID Instruction with EAX = 80000001h
Extended function 80000001h (EAX = 80000001h) of the
CPUID instruction returns the processor type, family,
model, and stepping information of the current processor
in EAX. The EBX and ECX registers are reserved.
Model-Specific Registers
(via RDMSR / WRMSR
Instructions)
EDX[6]
EDX[7]
EDX[8]
EDX[9]
EDX[10]
EDX[11]
0
0
1
0
0
0
Reserved
-
-
-
-
-
-
Machine Check Exception
CMPXCHG8B Instruction
Reserved
The extended feature flags supported are returned in the
EDX register as shown in Table 8-23. Each flag refers to a
specific feature and indicates if that feature is present on
the processor. Some of these features have protection
control in CR4. Before using any of these features on the
processor, the software should check the corresponding
feature flag.
Reserved
SYSCALL / SYSRET
Instruction
EDX[12]
EDX[13]
EDX[14]
EDX[15]
0
0
0
1
Reserved
-
-
-
-
Page Global Enable
Reserved
Integer Conditional Move
Instruction
EDX[16]
0
FPU Conditional Move
Instruction
-
EDX[22:17]
EDX[23]
0
1
1
Reserved
MMX
-
-
-
EDX[24]
6x86MX Multimedia
Extensions
Note: 0 = Not supported
www.national.com
220
Revision 1.1
NSC [ National Semiconductor ]
