Intel ARCHITECTURE IA-32 User Manual Page 357

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Vol. 3A 8-33
ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)
Section 8.10, “APIC Bus Message Passing Mechanism and Protocol (P6 Family, Pentium
Processors),” describes the APIC bus arbitration protocols and bus message formats, while
Section 8.6.1, “Interrupt Command Register (ICR),” describes the INIT level de-assert IPI
message.
Note that except for the SIPI IPI (see Section 8.6.1, “Interrupt Command Register (ICR)”), all
bus messages that fail to be delivered to their specified destination or destinations are automat-
ically retried. Software should avoid situations in which IPIs are sent to disabled or nonexistent
local APICs, causing the messages to be resent repeatedly.
8.8 HANDLING INTERRUPTS
When a local APIC receives an interrupt from a local source, an interrupt message from an I/O
APIC, or and IPI, the manner in which it handles the message depends on processor implemen-
tation, as described in the following sections.
8.8.1 Interrupt Handling with the Pentium 4 and Intel Xeon
Processors
With the Pentium 4 and Intel Xeon processors, the local APIC handles the local interrupts, inter-
rupt messages, and IPIs it receives as follows:
1. It determines if it is the specified destination or not (see Figure 8-16). If it is the specified
destination, it accepts the message; if it is not, it discards the message.
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 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 sets the
appropriate bit in the IRR.
Figure 8-16. Interrupt Acceptance Flow Chart for the Local APIC (Pentium 4 and Intel
Xeon Processors)
Wait to Receive
Bus Message
Belong
to
Destination?
Discard
Message
No
Accept
Message
Yes
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