AMD-K6-2E Datasheet, PDF (70/332 Pages) Advanced Micro Devices – AMD-K6™-2E Embedded Processor

AMD-K6™-2E Processor Data Sheet
Preliminary Information
22529B/0—January 2000
31
12 11 10 9 8 7 6 5 4 3 2 1 0
Physical Page Base Address
A
P P UW
V
DA CW / / P
L
DT SR
Symbol
Description
Bits
AVL
Available to Software
11–9
Reserved
8–7
D
Dirty
6
A
Accessed
5
PCD
Page Cache Disable
4
PWT
Page Writethrough
3
U/S
User/Supervisor
2
W/R
Write/Read
1
P
Present (valid)
0
Figure 46. Page Table Entry (PTE)
3.5
Descriptors and Gates
There are various types of structures and registers in the x86
architecture that define, protect, and isolate code segments,
data segments, task state segments, and gates. These structures
are called descriptors.
s The application segment descriptor is used to point to either a
data or code segment. Figure 47 on page 53 shows the
application segment descriptor format. Table 9 contains
information describing the memory segment type to which
the descriptor points.
s The system segment descriptor is used to point to a task state
segment, a call gate, or a local descriptor table. Figure 48 on
page 54 shows the system segment descriptor format. Table
10 contains information describing the type of segment or
gate to which the descriptor points.
s The AMD-K6-2E processor uses gates to transfer control
between executable segments with different privilege
levels. Figure 49 on page 55 shows the format of the gate
descriptor types. Table 10 contains information describing
the type of segment or gate to which the descriptor points.
52
Software Environment
Chapter 3