Intel IA-32 - Manual (Page 177)

Vol. 3A 5-1
CHAPTER 5
INTERRUPT AND EXCEPTION HANDLING
This chapter describes the processor’s interrupt and exception-handling mechanism when oper-
ating in protected mode. Most of the information provided here also applies to interrupt and
exception mechanisms used in real-address, virtual-8086 mode, and 64-bit mode.
Chapter 15, “8086 Emulation,” describes information specific to interrupt and exception mech-
anisms in real-address and virtual-8086 mode. Section 5.14, “Exception and Interrupt Handling
in 64-bit Mode,” describes information specific to interrupt and exception mechanisms in
IA-32e mode and 64-bit sub-mode.
5.1 INTERRUPT AND EXCEPTION OVERVIEW
Interrupts and exceptions are events that indicate that a condition exists somewhere in the
system, the processor, or within the currently executing program or task that requires the atten-
tion of a processor. They typically result in a forced transfer of execution from the currently
running program or task to a special software routine or task called an interrupt handler or an
exception handler. The action taken by a processor in response to an interrupt or exception is
referred to as servicing or handling the interrupt or exception.
Interrupts occur at random times during the execution of a program, in response to signals from
hardware. System hardware uses interrupts to handle events external to the processor, such as
requests to service peripheral devices. Software can also generate interrupts by executing the
INT n instruction.
Exceptions occur when the processor detects an error condition while executing an instruction,
such as division by zero. The processor detects a variety of error conditions including protection
violations, page faults, and internal machine faults. The machine-check architecture of the
Pentium 4, Intel Xeon, P6 family, and Pentium processors also permits a machine-check excep-
tion to be generated when internal hardware errors and bus errors are detected.
When an interrupt is received or an exception is detected, the currently running procedure or
task is suspended while the processor executes an interrupt or exception handler. When execu-
tion of the handler is complete, the processor resumes execution of the interrupted procedure or
task. The resumption of the interrupted procedure or task happens without loss of program conti-
nuity, unless recovery from an exception was not possible or an interrupt caused the currently
running program to be terminated.
This chapter describes the processor’s interrupt and exception-handling mechanism, when oper-
ating in protected mode. A description of the exceptions and the conditions that cause them to
be generated is given at the end of this chapter.