
20
AMD-K5 Processor
AMD K86 Family BIOS and Software Tools Developers Guide
21062E/0—June 1997
Preliminary Information
Segment Register Attributes
The selector portion of all segment registers is cleared. The
access rights and attribute fields are set up as shown in Table
10.
The limit fields are set to FFFFh. For CS, the base address is set
to FFFF_0000h; for all others the base address is 0. Note that
IDTR and GDTR consist of the just base and limit values, which
are initialized to 0 and FFFFh, respectively.
S
tate of the AMD-K5 Processor After INIT
The assertion of INIT causes the processor to empty its
pipelines, initialize most of its internal state, and branch to
address FFFF_FFF0h—the same instruction execution starting
point used after RESET. Unlike RESET, the processor
preserves the contents of its caches, the floating-point state, the
SMM base, MSRs, and the CD and NW bits of the CR0 register.
The edge-sensitive interrupts FLUSH# and SMI# are sampled
and preserved during the INIT process and are handled
accordingly after the initialization is complete. However, the
processor resets any pending NMI interrupt upon sampling
INIT asserted.
INIT can be used as an accelerator for 80286 code that requires
a reset to exit from Protected mode back to Real mode.
Table 10. Segment Register Attribute Fields Initial Values
Attribute Field
Value
0
0
1
0
1
2
Description
G
D/B
P
DPL
S
Type
Byte granularity
16-bit
Present
Privilege level
Application segment (except LDTR)
Data, read-write