Request Initiator Responsibilities; Central Agent Responsibilities; Observing Agent Responsibilities; Interrupt Acknowledge Transaction - Intel Pentium Pro Family Developer's Manual

BUS TRANSACTIONS AND OPERATIONS
REQa[4:0]#
read 0 1
write 0 1
Ab[15:8]#
x
These transactions drive REQa[0]#active if request initiated data is being sent. The Central
Agent will then drive TRDY#.
5.2.3.1.

REQUEST INITIATOR RESPONSIBILITIES

Generate the request with valid encodings. The reserved fields are driven inactive.
5.2.3.2.

CENTRAL AGENT RESPONSIBILITIES

Generate response for all encodings including all reserved encodings. Return data as necessary
5.2.3.3.

OBSERVING AGENT RESPONSIBILITIES

Observing agents must decode the entire request field and determine if they are required to take
any action. Of course, any agent may stall the Snoop Result Phase to delay completion.
5.2.3.4.

INTERRUPT ACKNOWLEDGE TRANSACTION

A processor agent issues an Interrupt Acknowledge Transaction in response to an interrupt from
an 8259A or similar interrupt controller. The response agent (normally the I/O agent) must per-
form whatever handshaking the interrupt controller requires. For example, an I/O agent inter-
faced to an 8259A interrupt controller must issue two locked-interrupt-acknowledge cycles to
the 8259A to process one Interrupt Acknowledge Transaction it receives from a Pentium Pro
processor. The I/O agent returns the interrupt vector generated by the 8259A to the processor as
a single data-cycle response on D[7:0]#. D[63:8]# are undefined. Note that the BE[7:0]# field
reflects this. The address Aa[35:3]# signals are reserved and can be driven to any value.
REQa[0]#
0
5-8
0 0 W/R#=0
0 0 W/R#=1
SMMEM# SPLCK#=0
REQb[1:0]#
0 0
REQb[4:0]#
DSZ[1:0]# rsvd
Ab[7:3]#
rsvd DEN#
Ab[15:8]#
01
x x
rsvd