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IRET            Interrupt Return                     Flags: O D I T S Z A P C
                                                            * * * * * * * * *
IRET                                                 IOv86
IRETD  (CPU: 386+)                                   IOv86

        Logic   ; Real mode
                POP IP
                POP CS
                POPF

    In real address mode, IRET pops the instruction pointer, CS, and
    the flags register from the stack and resumes the interrupted
    routine.

    In protected mode, the action of IRET depends on the setting of
    the nested task flag (NT) bit in the flags register. When popping
    the new flag image from the stack, the IOPL bits in the flags
    register are changed only when the current privilege level (CPL)
    is zero.
    - If NT = 0, IRET returns from an interrupt procedure without a
      task switch. The code returned to must be equally or less
      privileged than the interrupt routine (as indicated by the RPL
      bits of the CS selector popped from the stack). If the
      destination code is less privileged, IRET also pops the stack
      pointer and SS from the stack.
    - If NT = 1, IRET reverses the operation of a CALL or INT that
      caused a task switch. The updated state of the task executing
      IRET is saved in its task state segment. If the task is
      re-entered later, the code that follows IRET is executed.

    This instruction is IOPL-sensitive in V86 mode.


    Note
    Some assemblers support an IRET extension (IRETW) that forces a
    16-bit word-style pop into the FLAGS register regardless of the
    code segment's size attribute (80386+).

        
    Opcode      Format
    CF          IRET
    CF          IRETD


    Length and timing
    Operands    Bytes   8088    186     286     386     486     Pentium
    -             1     44      28      17+m    22      15     8-27  NP

                  32-bit return from interrupt (386+)
    -             1                             22      15    10-27  NP

                      Task switch clocks not shown