Intel 64 and IA-32 Architectures Software Developers Manual Volume 2B, Instruction Set Reference, N-Z

4-16 Vol. 2B
INSTRUCTION SET REFERENCE, N-Z
executed until the EWBE# pin is sampled active.) Only the Pentium processor family
has the EWBE# pin.
Operation
IF ((PE = 1) and ((CPL > IOPL) or (VM = 1)))
THEN (* Protected mode with CPL > IOPL or virtual-8086 mode *)
IF (Any I/O Permission Bit for I/O port being accessed
= 1)
THEN (* I/O operation is not allowed *)
#GP(0);
ELSE ( * I/O operation is allowed *)
DEST ← SRC; (* Writes to selected I/O port *)
FI;
ELSE (Real Mode or Protected Mode with CPL ≤ IOPL *)
DEST ← SRC; (* Writes to selected I/O port *)
FI;
Flags Affected
None.
Protected Mode Exceptions
#GP(0) If the CPL is greater than (has less privilege) the I/O privilege
level (IOPL) and any of the corresponding I/O permission bits in
TSS for the I/O port being accessed is 1.
Real-Address Mode Exceptions
None.
Virtual-8086 Mode Exceptions
#GP(0) If any of the I/O permission bits in the TSS for the I/O port being
accessed is 1.
#PF(fault-code) If a page fault occurs.
Compatibility Mode Exceptions
Same as protected mode exceptions.
64-Bit Mode Exceptions
Same as protected mode exceptions.