6-22 Vol. 3A

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 regis-
ters 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.