Vol. 3A 10-27
ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)
interrupts) send a message on the bus indicating that the interrupt handling has been completed. (A write to
the EOI register must not be included in the handler routine for an NMI, SMI, INIT, ExtINT, or SIPI.)
10.8.2
Interrupt Handling with the P6 Family and Pentium Processors
With the P6 family and Pentium processors, the local APIC handles the local interrupts, interrupt messages, and
IPIs it receives as follows (see Figure 10-17).
1. (IPIs only) It examines the IPI message to determines if it is the specified destination for the IPI as described
in Section 10.6.2, “Determining IPI Destination.” If it is the specified destination, it continues its acceptance
procedure; if it is not the destination, it discards the IPI message. When the message specifies lowest-priority
delivery mode, the local APIC will arbitrate with the other processors that were designated on recipients of the
IPI message (see Section 10.6.2.4, “Lowest Priority Delivery Mode”).
2. If the local APIC determines that it is the designated destination for the interrupt and if the interrupt request is
an NMI, SMI, INIT, ExtINT, or INIT-deassert interrupt, or one of the MP protocol IPI messages (BIPI, FIPI, and
SIPI), the interrupt is sent directly to the processor core for handling.
3. If the local APIC determines that it is the designated destination for the interrupt but the interrupt request is
not one of the interrupts given in step 2, the local APIC looks for an open slot in one of its two pending interrupt
queues contained in the IRR and ISR registers (see Figure 10-20). If a slot is available (see Section 10.8.4,
“Interrupt Acceptance for Fixed Interrupts”), places the interrupt in the slot. If a slot is not available, it rejects
the interrupt request and sends it back to the sender with a retry message.
Figure 10-17. Interrupt Acceptance Flow Chart for the Local APIC (P6 Family and Pentium Processors)
Wait to Receive
Bus Message
Belong
to
Destination?
Is it
NMI/SMI/INIT
/ExtINT?
Delivery
Am I
Focus?
Other
Focus?
Is Interrupt Slot
Available?
Is Status a
Retry?
Discard
Message
Accept
Message
Yes
Yes
Accept
Message
Is Interrupt
Slot Avail-
able?
Arbitrate
Yes
Am I Winner?
Accept
Message
Yes
No
Set Status
to Retry
No
No
Yes
Set Status
to Retry
No
Discard
Message
No
Accept
Message
Yes
Lowes
Priority
Fixed
Yes
No
No
Yes
No
P6 Family
Processor Specific