Intel 253668-032US 10.9.4 Interrupt Acceptance for Fixed Interrupts

Vol. 3 10-59
ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)
Its value in the PPR is computed as follows:
IF TPR[7:4] ≥ ISRV[7:4]
THEN
PPR[7:0] ← TPR[7:0]
ELSE
PPR[7:4] ← ISRV[7:4]
PPR[3:0] ← 0
Here, the ISRV value is the vector number of the highest priority ISR bit that is set,
or 00H if no ISR bit is set. Essentially, the processor priority is set to either to the
highest priority pending interrupt in the ISR or to the current task priority, whichever
is higher.
10.9.4 Interrupt Acceptance for Fixed Interrupts
The local APIC queues the fixed interrupts that it accepts in one of two interrupt
pending registers: the interrupt request register (IRR) or in-service register (ISR).
These two 256-bit read-only registers are shown in Figure 10-28. The 256 bits in
these registers represent the 256 possible vectors; vectors 0 through 15 are
reserved by the APIC (see also: Section 10.6.2, “Valid Interrupt Vectors”).
NOTE
All interrupts with an NMI, SMI, INIT, ExtINT, start -up, or INIT-
deassert delivery mode bypass the IRR and ISR registers and are
sent directly to the processor core for servicing.
Figure 10-27. Processor Priority Register (PPR)
31 078
Reserved
Address: FEE0 00A0H
Value after reset: 0H Processor Priority Sub-Class
Processor Priority
43