307013-003 Datasheet, PDF (139/848 Pages) Intel Corporation – Intel I/O Controller Hub 7

Functional Description
5.9.5
5.9.5.1
5.9.5.2
5.9.6
Masking Interrupts
Masking on an Individual Interrupt Request
Each interrupt request can be masked individually by the Interrupt Mask Register
(IMR). This register is programmed through OCW1. Each bit in the IMR masks one
interrupt channel. Masking IRQ2 on the master controller masks all requests for service
from the slave controller.
Special Mask Mode
Some applications may require an interrupt service routine to dynamically alter the
system priority structure during its execution under software control. For example, the
routine may wish to inhibit lower priority requests for a portion of its execution but
enable some of them for another portion.
The special mask mode enables all interrupts not masked by a bit set in the Mask
register. Normally, when an interrupt service routine acknowledges an interrupt without
issuing an EOI to clear the ISR bit, the interrupt controller inhibits all lower priority
requests. In the special mask mode, any interrupts may be selectively enabled by
loading the Mask Register with the appropriate pattern. The special mask mode is set
by OCW3 where: SSMM=1, SMM=1, and cleared where SSMM=1, SMM=0.
Steering PCI Interrupts
The ICH7 can be programmed to allow PIRQA#-PIRQH# (PIRQE#–PIRQH# on Ultra
Mobile) to be internally routed to interrupts 3–7, 9–12, 14 or 15. The assignment is
programmable through the through the PIRQx Route Control registers, located at 60–
63h and 68–6Bh in Device 31:Function 0. 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.
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
specified IRQ line, software must change the IRQ's corresponding ELCR bit to level
sensitive mode. The ICH7 internally inverts the PIRQx# line to send an active high level
to the PIC. When a PCI interrupt is routed onto the PIC, the selected IRQ can no longer
be used by an active high device (through SERIRQ). However, active low interrupts can
share their interrupt with PCI interrupts.
Internal sources of the PIRQs, including SCI and TCO interrupts, cause the external
PIRQ to be asserted. The ICH7 receives the PIRQ input, like all of the other external
sources, and routes it accordingly.
Intel ^® ICH7 Family Datasheet
139