Functional Description
5.8.2.2
5.8.2.3
ICW2
The second write in the sequence (ICW2) is programmed to provide bits [7:3] of the
interrupt vector that will be released during an interrupt acknowledge. A different base
is selected for each interrupt controller.
ICW3
The third write in the sequence (ICW3) has a different meaning for each controller.
• For the master controller, ICW3 is used to indicate which IRQ input line is used to
cascade the slave controller. Within the ICH10, IRQ2 is used. Therefore, bit 2 of
ICW3 on the master controller is set to a 1, and the other bits are set to 0s.
• For the slave controller, ICW3 is the slave identification code used during an
interrupt acknowledge cycle. On interrupt acknowledge cycles, the master
controller broadcasts a code to the slave controller if the cascaded interrupt won
arbitration on the master controller. The slave controller compares this
identification code to the value stored in its ICW3, and if it matches, the slave
controller assumes responsibility for broadcasting the interrupt vector.
5.8.2.4
ICW4
The final write in the sequence (ICW4) must be programmed for both controllers. At
the very least, bit 0 must be set to a 1 to indicate that the controllers are operating in
an Intel Architecture-based system.
5.8.3
Operation Command Words (OCW)
These command words reprogram the Interrupt controller to operate in various
interrupt modes.
• OCW1 masks and unmasks interrupt lines.
• OCW2 controls the rotation of interrupt priorities when in rotating priority mode,
and controls the EOI function.
• OCW3 sets up ISR/IRR reads, enables/disables the special mask mode (SMM), and
enables/disables polled interrupt mode.
5.8.4
Modes of Operation
5.8.4.1
Fully Nested Mode
In this mode, interrupt requests are ordered in priority from 0 through 7, with 0 being
the highest. When an interrupt is acknowledged, the highest priority request is
determined and its vector placed on the bus. Additionally, the ISR for the interrupt is
set. This ISR bit remains set until: the processor issues an EOI command immediately
before returning from the service routine; or if in AEOI mode, on the trailing edge of
the second INTA#. While the ISR bit is set, all further interrupts of the same or lower
priority are inhibited, while higher levels generate another interrupt. Interrupt priorities
can be changed in the rotating priority mode.
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Datasheet
INTEL [ INTEL ]
