Specifications

Intel

Quark SoC X1000 Core

October 2013 Developer’s Manual

Order Number: 329679-001US 73

Protected Mode Architecture—Intel

Quark Core

granularity is unrelated to paging. A Intel

Quark SoC X1000 Core system can consist

of segments with byte granularity and page granularity, whether or not paging is

enabled.

The executable (E) bit tells if a segment is a code or data segment. A code segment

(E=1, S=1) may be execute-only or execute/read as determined by the Read (R) bit.

Code segments are execute-only if R=0, and execute/read if R=1. Code segments may

never be written to.

Note: Code segments can be modified via aliases. Aliases are writeable data segments that

occupy the same range of linear address space as the code segment.

The D bit indicates the default length for operands and effective addresses. If D=1, 32-

bit operands and 32-bit addressing modes are assumed. When D=0, 16-bit operands

and 16-bit addressing modes are assumed.

Another attribute of code segments is determined by the conforming (C) bit.

Conforming segments, indicated when C=1, can be executed and shared by programs

at different privilege levels (see Section 6.3).

Figure 28. Segment Descriptors

31 0Byte

Address

Segment Base 15...0 Segment Limit 15...0

Base 31...24 G D 0 AVL

Limit

19...16

DPL

Type

A Base 23...16

BASE Base Address of the segment

LIMIT The length of the segment

P Present Bit 1=Present, 0=Not Present

DPL Descriptor Privilege Level 0–3

S Segment Descriptor 0=System Descriptor, 1=Code or Data Segment Descriptor

TYPE Type of Segment

A Accessed Bit

G Granularity Bit 1=Segment length is page granular, 0=Segment length is byte granular

D Default Operation Size (recognized in code segment descriptors only)

1=32-bit segment, 0=16-bit segment

0 Bit must be zero (0) for compatibility with future processors

AVL Available field for user or OS

Note: In a maximum-size segment (i.e., a segment with G=1 and segment limit 19...0=FFFFFH), the

lowest 12 bits of the segment base should be zero (i.e., segment base 11...000=000H).