GX1 Datasheet, PDF (218/247 Pages) National Semiconductor (TI) – Processor Series Low Power Integrated x86 Solution

Instruction Set (Continued)
8.2 CPUID INSTRUCTION
The CPUID instruction (opcode 0FA2) allows the software
to make processor inquiries as to the vendor, family, model,
stepping, features and also provides cache information.
The GX1 supports both the standard and National Semi-
conductor extended CPUID levels.
The presence of the CPUID instruction is indicated by the
ability to change the value of the ID Flag, bit 21 in the
EFLAGS register.
The CPUID level allows the CPUID instruction to return dif-
ferent information in the EAX, EBX, ECX, aand EDX regis-
ters. The level is determined by the initialized value of the
EAX register before the instruction is executed. A summary
of the CPUID levels is shown in Table 8-16.
Table 8-16. CPUID Levels Summary
CPUID
Type
Initialized
EAX
Register
Returned Data in EAX, EBX,
ECX, EDX Registers
Standard
Standard
Standard
Extended
Extended
Extended
Extended
Extended
Extended
00000000h
00000001h
00000002h
80000000h
80000001h
80000002h
80000003h
80000004h
80000005h
Maximum standard levels, CPU
vendor string
Model, family, type and features
TLB and cache information
Maximum extended levels
Extended model, family, type and
features
CPU marketing name string
TLB and L1 cache description
8.2.1 Standard CPUID Levels
The standard CPUID levels are part of the standard x86
instruction set.
8.2.1.1 CPUID Instruction with EAX = 0000 0000h
Standard function 0h (EAX = 0) of the CPUID instruction
returns the maximum standard CPUID levels as well as the
processor vendor string.
After the instruction is executed, the EAX register contains
the maximum standard CPUID levels supported. The maxi-
mum standard CPUID level is the highest acceptable value
for the EAX register input. This does not include the
extended CPUID levels.
The EBX through EDX registers contain the vendor string
of the processor as shown in Table 8-17.
Table 8-17. CPUID Data Returned when EAX = 0
Register¹
Returned Contents
Description
EAX
EBX
EDX
ECX
2
64
6F
(doeG)
79
62
(yb e)
43
53
(CSN )
6547
Maximum Standard
Level
Vendor ID String 1
2065 Vendor ID String 2
4E20 Vendor ID String 3
1. The register column is intentionally out of order.
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