Specifications

Intel
®
Quark SoC X1000 Core
October 2013 Developer’s Manual
Order Number: 329679-001US 83
Protected Mode Architecture—Intel
®
Quark Core
6.3.3.3 I/O Privilege and I/O Permission Bitmap
The I/O privilege level (IOPL, a 2-bit field in the EFLAG register) defines the least
privileged level at which I/O instructions can be unconditionally performed. I/O
instructions can be unconditionally performed when CPL ≥ IOPL. (The I/O instructions
are IN, OUT, INS, OUTS, REP INS, and REP OUTS.) When CPL > IOPL and the current
task is associated with a 286 TSS, attempted I/O instructions cause an exception 13
fault. When CPL > IOPL and the current task is associated with a Intel
®
Quark SoC
X1000 Core TSS, the I/O permission bitmap (part of a Intel
®
Quark SoC X1000 Core
TSS) is consulted on whether I/O to the port is allowed; otherwise an exception 13 fault
is generated. For diagrams of the I/O Permission Bitmap, refer to Figure 36 and
Figure 37. For further information on how the I/O Permission Bitmap is used in
Protected Mode or in Virtual 8086 Mode, refer to Section 6.5.4.
The I/O privilege level (IOPL) also affects whether several other instructions can be
executed or whether an exception 13 fault should be generated. These instructions,
called “IOPL-sensitive” instructions, are CLI and STI. (Note that the LOCK prefix is not
IOPL-sensitive on the Intel
®
Quark SoC X1000 Core.)