Datasheet

Functional Description
Intel® Xeon® Processor D-1500 Product Family 79
Datasheet - Volume 1 of 4: Integrated Platform Controller Hub
March 2015
5. Upon receiving the first internally generated INTA# pulse, the highest priority ISR
bit is set and the corresponding IRR bit is reset. On the trailing edge of the first
pulse, a slave identification code is broadcast by the master to the slave on a
private, internal three bit wide bus. The slave controller uses these bits to
determine if it must respond with an interrupt vector during the second
INTA# pulse.
6. Upon receiving the second internally generated INTA# pulse, the PIC returns the
interrupt vector. If no interrupt request is present because the request was too
short in duration, the PIC returns vector 7 from the master controller.
7. This completes the interrupt cycle. In AEOI mode the ISR bit is reset at the end of
the second INTA# pulse. Otherwise, the ISR bit remains set until an appropriate
EOI command is issued at the end of the interrupt subroutine.
3.8.2 Initialization Command Words (ICWx)
Before operation can begin, each 8259 must be initialized. In Intel® Xeon® Processor
D-1500 Product Family, this is a four byte sequence. The four initialization command
words are referred to by their acronyms: ICW1, ICW2, ICW3, and ICW4.
The base address for each 8259 initialization command word is a fixed location in the
I/O memory space: 20h for the master controller, and A0h for the slave controller.
3.8.2.1 ICW1
An I/O write to the master or slave controller base address with data bit 4 equal to 1 is
interpreted as a write to ICW1. Upon sensing this write, Intel® Xeon® Processor D-
1500 Product Family’s PIC expects three more byte writes to 21h for the master
controller, or A1h for the slave controller, to complete the ICW sequence.
A write to ICW1 starts the initialization sequence during which the following
automatically occur:
1. Following initialization, an interrupt request (IRQ) input must make a low-to-high
transition to generate an interrupt.
2. The Interrupt Mask Register is cleared.
3. IRQ7 input is assigned priority 7.
4. The slave mode address is set to 7.
5. Special mask mode is cleared and Status Read is set to IRR.
3.8.2.2 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.
3.8.2.3 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 Intel® Xeon® Processor D-1500 Product
Family, IRQ2 is used. Therefore, Bit 2 of ICW3 on the master controller is set to a 1,
and the other bits are cleared to 0s.