AMD-K6 datasheet(300/346 Pages) AMD

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Software Environment

Chapter 24

AMD-K6® Processor Data Sheet

20695H/0—March 1998

Preliminary Information

Fo r mo re in fo rma tio n ab o ut the RD MSR and WRMSR

instructions, see the AMD K86™ Family BIOS and Software Tools

Development Guide, order# 21062.

Extended Feature Enable Register (EFER). T h e E x t e nd ed Fe at u re

Enable Register (EFER) contains the control bits that enable

the extended features of the AMD-K6. Figure 102 shows the

format of the EFER register, and Table 60 defines the function

of each bit in the EFER register.

Figure 102. Extended Feature Enable Register (EFER)

SYSCALL/SYSRET Target Address Register (STAR).

The SYSCALL/SYSRET Target Address Register (STAR)

contains the target EIP a ddre ss used by the SYSCALL

instruction and the 16-bit code and stack segment selector

bases used by the SYSCALL and SYSRET instructions. Figure

103 shows the format of the STAR register, and Table 61 defines

the function of each bit of the STAR register. For more

information, see the SYSCALL and SYSRET Instruction

Specification Application Note, order# 21086.

Table 59. Model-Specific Registers (MSRs)

Model-Specific Register

Value of ECX

Extended Feature Enable Register (EFER)

C000_0080h

SYSCALL/SYSRET Target Address Register (STAR)

C000_0081h

Reserved

Symbol

Description

Bit

SCE

System Call/Return Extension

Table 60. Extended Feature Enable Register (EFER) Definition

Bit

Description

R/W

63–1

Reserved

System Call/Return Extension (SCE)

R/W

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