EP80579 Datasheet, PDF (1129/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
30.2.4.4
30.2.5
30.2.6
30.2.6.1
30.2.6.2
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.
ICW4
The final write in the sequence, ICW4, must be programmed by 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.
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.
Modes of Operation
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.
Special Fully Nested Mode
This mode is used in the case of a system where cascading is used, and the priority has
to be conserved within each slave. In this case, the special fully-nested mode is
programmed to the master controller. This mode is similar to the fully-nested mode
with the following exceptions:
• When an interrupt request from a certain slave is in service, this slave is not locked
out from the master's priority logic and further interrupt requests from higher
priority interrupts within the slave is recognized by the master and initiates
interrupts to the processor. In normal nested mode, a slave is masked out when its
request is in service.
• When exiting the Interrupt Service routine, software has to check whether the
interrupt serviced was the only one from that slave. This is done by sending a Non-
Specific EOI command to the slave and then reading its ISR. If it is 0, a non-
specific EOI can also be sent to the master.
August 2009
Order Number: 320066-003US
Intel^® EP80579 Integrated Processor Product Line Datasheet
1129