I/O Privilege And I/O Permission Bitmap - Intel Quark SoC X1000 Core Developer's Manual

Protected Mode Architecture—Intel
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
X1000 Core TSS, the I/O permission bitmap (part of a Intel
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 37. For further information on how the I/O Permission Bitmap is used in
Protected Mode or in Virtual 8086 Mode, refer to
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
October 2013
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Quark Core
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Quark SoC X1000 Core.)
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Quark SoC X1000 Core
Figure 36
Section 6.5.4.
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Intel Quark SoC X1000 Core
Developer's Manual
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