Chapter 9 Exceptions and Interrupts

Interrupts and exceptions are special kinds of control transfer; they work somewhat like unprogrammed CALLs. They alter the normal program flow to handle external events or to report errors or exceptional conditions. The difference between interrupts and exceptions is that interrupts are used to handle asynchronous events external to the processor, but exceptions handle conditions detected by the processor itself in the course of executing instructions.

There are two sources for external interrupts and two sources for exceptions:

1. Interrupts
   • Maskable interrupts, which are signalled via the INTR pin.
   • Nonmaskable interrupts, which are signalled via the NMI (Non-Maskable Interrupt) pin.
2. Exceptions
   • Processor detected. These are further classified as faults, traps, and aborts.
   • Programmed. The instructions INTO, INT 3, INT n, and BOUND can trigger exceptions. These instructions are often called "software interrupts", but the processor handles them as exceptions.

9.1 Identifying Interrupts
9.2 Enabling and Disabling Interrupts
9.3 Priority Among Simultaneous Interrupts and Exceptions
9.4 Interrupt Descriptor Table
9.5 IDT Descriptors
9.6 Interrupt Tasks and Interrupt Procedures
9.7 Error Code
9.8 Exception Conditions
9.9 Exception Summary
9.10 Error Code Summary

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