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Vol. 3 10-15
ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)
• The mask bits for all the LVT entries are set. Attempts to reset these bits will be
ignored.
• (For Pentium and P6 family processors) The local APIC continues to listen to all
bus messages in order to keep its arbitration ID synchronized with the rest of the
system.
10.4.7.3 Local APIC State After an INIT Reset (“Wait-for-SIPI” State)
An INIT reset of the processor can be initiated in either of two ways:
• By asserting the processor’s INIT# pin.
• By sending the processor an INIT IPI (an IPI with the delivery mode set to INIT).
Upon receiving an INIT through either of these mechanisms, the processor responds
by beginning the initialization process of the processor core and the local APIC. The
state of the local APIC following an INIT reset is the same as it is after a power-up or
hardware RESET, except that the APIC ID and arbitration ID registers are not
affected. This state is also referred to at the “wait-for-SIPI” state (see also:
Section
8.4.2, “MP Initialization Protocol Requirements and Restrictions”).
10.4.7.4 Local APIC State After It Receives an INIT-Deassert IPI
Only the Pentium and P6 family processors support the INIT-deassert IPI. An INIT-
disassert IPI has no affect on the state of the APIC, other than to reload the arbitra-
tion ID register with the value in the APIC ID register.
10.4.8 Local APIC Version Register
The local APIC contains a hardwired version register. Software can use this register to
identify the APIC version (see Figure 10-7). In addition, the register specifies the
number of entries in the local vector table (LVT) for a specific implementation.
The fields in the local APIC version register are as follows:
Version The version numbers of the local APIC:
1XH Local APIC. For Pentium 4 and Intel Xeon
processors, 14H is returned.
0XH 82489DX external APIC.
20H - FFH Reserved.
Max LVT Entry Shows the number of LVT entries minus 1. For the Pentium 4 and
Intel Xeon processors (which have 6 LVT entries), the value
returned in the Max LVT field is 5; for the P6 family processors
(which have 5 LVT entries), the value returned is 4; for the
Pentium processor (which has 4 LVT entries), the value returned
is 3.