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Hardware Specification
Version 1.4 3-9
3.6.2.2 Virtual Wire Mode
Virtual Wire Mode provides a uniprocessor hardware environment capable of booting and running
all DOS shrink-wrapped software.
In Virtual Wire Mode, as shown in Figure 3-3, the 8259A-equivalent PIC fields all interrupts, and
the local APIC of the BSP becomes a virtual wire, which delivers interrupts from the PIC to the
BSP via the local APIC’s local interrupt 0 (LINTIN0). The LINTIN0 pin of the local APIC is
programmed as ExtINT, specifying to the APIC that the PIC is to serve as an external interrupt
controller. Whenever the local APIC finds that a particular interrupt is of type ExtINT, it asserts
the ExtINTA transaction along with the PINT interrupt to the processor. In this case, the I/O APIC
is not used.
LINTIN0 LINTIN1
NMI
NMI
INTR
CPU 1
LINTIN0 LINTIN1 LINTIN0 LINTIN1
NMI INTR
CPU 2
NMI INTR
CPU 3
REG.
MARK
BSP AP1 AP2
LOCAL
APIC
1
LOCAL
APIC
2
LOCAL
APIC
3
RESET
LINTIN0
LINTIN1
ICC BUS
INTR
I/O
APIC
8259A-
EQUIVALENT
PICS
INTERRUPT INPUTS
SHADED AREAS INDICATE UNUSED CIRCUITS. DOTTED LINE SHOWS INTERRUPT PATH.
Figure 3-3. Virtual Wire Mode via Local APIC