SB82371 Intel Corporation, SB82371 Datasheet - Page 105

• Manufacturer Part Number: SB82371
• Description: 82371FB (PIIX) AND 82371SB (PIIX3) PCI ISA IDE XCELERATOR
• Manufacturer: Intel Corporation

registers. One or more PIRQx# lines can be routed to the same IRQx input. If interrupt steering is not
required, the Route Registers can be programmed to disable steering.
For the PIIX3, the Universal Serial Bus (USB) Module interrupt is hardwired to the PIRQD# signal. When the
USB is enabled, the USB Host Controller in PIIX3 uses the PIRQD# input to the internal interrupt controller. If
an IOAPIC is used, the USB outputs interrupts on PIRQD# to the external IOAPIC. When the USB function is
disabled, other PCI devices can use the PIRQD# input.
The PIRQx# lines are defined as active low, level sensitive to allow multiple interrupts on a PCI Board to
share a single line across the connector. When a PIRQx# is routed to a specified IRQ line, the software must
change the IRQ’s corresponding ELCR bit to level sensitive mode. Note, that this means that the selected
IRQ can no longer be used by an ISA device, unless that ISA device can respond as an active low level
sensitive interrupt.
The 82371FB PIIX supports up to two programmable interrupts (MIRQ[1:0]; intended for use with
motherboard devices) to be routed to one of the 11 interupts (IRQ[15,14,12:9,7:3]) using the MBIRQx Route
Control Register. The routing is accomplished in the same manner as for the PIRQx# inputs, except that the
interrupts are active high. Two MIRQx lines may be routed to the same IRQx input. If interrupt steering is not
required, the MBIRQx registers can be programmed to disable routing. Note that only one motherboard
interrupt (MIRQ0) is available on PIIX3.
For the 82371FB PIIX , when more than one MIRQ line is routed to an IRQ input, the software must change
the IRQ’s corresponding ELCR bit to level sensitive mode. Interrupt sharing for motherboard devices must be
evaluated for the particular combination of devices under consideration. The IRQ selected bit MBIRQx[3:0]
can no longer be used by an ISA device, unless that ISA device can respond as an active high level sensitive
interrupt.
Note: MIRQ1 is only availabe on PIIX. MIRQ0 is available on both PIIX and PIIX3.
3.9.
The PIIX3 supports a stand-alone IOAPIC device on the ISA X-Bus. The PIIX3 provides a chip select signal
(APICCS#) for the IOAPIC. It also provides handshake signals to maintain buffer coherency in the IOAPIC
environment.
Stand-Alone IOAPIC Support (PIIX3)
(PIIX and PIIX3)
(PIIX Only)
IRQ[15:9,8#,7:1]
PIRQ[A:C]#
PIRQD#
MIRQ1
MIRQ0
Figure 8. Interrupt Steering
PIIX/PIIX3
Interrupt
82371FB (PIIX) AND 82371SB (PIIX3)
(PIIX3 Only)
Serial Bus
Universal
Interrupt
Steering
Module
Logic
Internal
82C59s
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