User's Manual

6-30 Vol. 3
INTERRUPT AND EXCEPTION HANDLING
Interrupt 2—NMI Interrupt
Exception Class Not applicable.
Description
The nonmaskable interrupt (NMI) is generated externally by asserting the
processor’s NMI pin or through an NMI request set by the I/O APIC to the local APIC.
This interrupt causes the NMI interrupt handler to be called.
Exception Error Code
Not applicable.
Saved Instruction Pointer
The processor always takes an NMI interrupt on an instruction boundary. The saved
contents of CS and EIP registers point to the next instruction to be executed at the
point the interrupt is taken. See
Section 6.5, “Exception Classifications,” for more
information about when the processor takes NMI interrupts.
Program State Change
The instruction executing when an NMI interrupt is received is completed before the
NMI is generated. A program or task can thus be restarted upon returning from an
interrupt handler without loss of continuity, provided the interrupt handler saves the
state of the processor before handling the interrupt and restores the processor’s
state prior to a return.