Specifications

Intel
®
Quark Core—Protected Mode Architecture
Intel
®
Quark SoC X1000 Core
Developer’s Manual October 2013
76 Order Number: 329679-001US
parameters are to be copied from the caller's stack to the stack of the called routine.
The word count field is only used by call gates when there is a change in the privilege
level; other types of gates ignore the word count field.
Figure 30. Gate Descriptor Formats
Interrupt and trap gates use the destination selector and destination offset fields of the
gate descriptor as a pointer to the start of the interrupt or trap handler routines. The
difference between interrupt gates and trap gates is that the interrupt gate disables
interrupts (resets the IF bit), whereas the trap gate does not.
Task gates are used to switch tasks. Task gates may only refer to a task state segment
(see Section 6.3.6). Therefore, only the destination selector portion of a task gate
descriptor is used, and the destination offset is ignored.
Exception 13 is generated when a destination selector does not refer to a correct
descriptor type, i.e., a code segment for an interrupt, trap or call gate, or a TSS for a
task gate.
The access byte format is the same for all gate descriptors. P=1 indicates that the gate
contents are valid. P=0 indicates the contents are not valid and causes exception 11
when referenced. DPL is the descriptor privilege level and specifies when this descriptor
may be used by a task (see Section 6.3). The S field, bit 4 of the access rights byte,
must be 0 to indicate a system control descriptor. The type field specifies the descriptor
type as indicated in Figure 30.
Gate Descriptor Fields
Name Value Description
Type 4 80286 call gate
5 Task gate (for 80286 or Intel
®
Quark SoC X1000 Core task)
6 80286 interrupt gate
7 80286 trap gate
CIntel
®
Quark SoC X1000 Core call gate
EIntel
®
Quark SoC X1000 Core interrupt gate
FIntel
®
Quark SoC X1000 Core trap gate
P 0 Descriptor contents are not valid
1 Descriptor contents are valid
DPL—least privileged level at which a task may access the gate. WORD COUNT 0–31—the number of
parameters to copy from caller's stack to the called procedure's stack. The parameters are 32-bit quan-
tities for Intel
®
Quark SoC X1000 Core gates, and 16-bit quantities for 80286 gates.
DESTINATION 16-bit Selector to the target code segment
SELECTOR selector or
Selector to the target task state segment for task gate
DESTINATION offset Entry point within the target code segment
OFFSET 16-bit 80286
32-bit Intel
®
Quark SoC X1000 Core
31 24 16 8 5 0 Byte
Address
0
Selector Offset 15...0
Offset 31...16 P
DPL
0
Type
000
Word
Count
4...0
+4