Segment Register Usage; Address Translation - Intel Quark SoC X1000 Core Developer's Manual

Figure 2.

Address Translation

Effective Address Calculation
Base
15 3 2
R
Selector
P
L
Segment Register
3.3.2

Segment Register Usage

The main data structure used to organize memory is the segment. On the Intel
SoC X1000 Core, segments are variable sized blocks of linear addresses which have
certain attributes associated with them. There are two main types of segments: code
and data. The segments are of variable size and can be as small as 1 byte or as large
as 4 Gbytes (2
In order to provide compact instruction encoding, and increase Intel
X1000 Core performance, instructions do not need to explicitly specify which segment
register is used. A default segment register is automatically chosen according to the
rules of Table
register; stack references use the SS register and Instruction fetches use the CS
register. The contents of the Instruction Pointer provide the offset. Special segment
override prefixes allow the explicit use of a given segment register, and override the
implicit rules listed in
GS segment registers.
There are no restrictions regarding the overlapping of the base addresses of any
segments. Thus, all 6 segments could have the base address set to zero and create a
system with a 4-Gbyte linear address space. This creates a system where the virtual
address space is the same as the linear address space. Further details of segmentation
are discussed in
®
Intel Quark SoC X1000 Core
Developer's Manual
24
Index
Displacement
X
Scale
1, 2, 3, 4
+
Effective
Address
32 Segmentation
Unit
Logical or
0
Virtual Address
13
Descriptor Index
32
bytes).
3. In general, data references use the selector contained in the DS
Table 3. The override prefixes also allow the use of the ES, FS and
Chapter 6.0, "Protected Mode Architecture."
®
Intel Quark Core—Architectural Overview
BE3#–BE0#
A31–A2
Paging Unit
(optional use)
32 32
Linear Physical
Address Address
31 0
Physical
Memory
A5158-01
®
Quark
®
Quark SoC
October 2013
Order Number: 329679-001US