STI -- Set Interrupt Flag

Opcode  Instruction   Clocks   Description

F13     STI           3        Set interrupt flag; interrupts enabled at the
                               end of the next instruction

Operation

IF := 1

Description

STI sets the interrupt flag to 1. The 80386 then responds to external interrupts after executing the next instruction if the next instruction allows the interrupt flag to remain enabled. If external interrupts are disabled and you code STI, RET (such as at the end of a subroutine), the RET is allowed to execute before external interrupts are recognized. Also, if external interrupts are disabled and you code STI, CLI, then external interrupts are not recognized because the CLI instruction clears the interrupt flag during its execution.

Flags Affected

IF := 1

Protected Mode Exceptions

#GP(0) if the current privilege level is greater (has less privilege) than the I/O privilege level

Real Address Mode Exceptions

None

Virtual 8086 Mode Exceptions

None

up: Chapter 17 -- 80386 Instruction Set
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