Intel
®
81341 and 81342—Address Translation Unit (PCI-X)
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
72
Order Number: 315037-002US
2.2.2
Outbound Transactions- Single Address Cycle (SAC) Internal
Bus Transactions
Outbound transactions initiated by the 81341 and 81342 core processor are directed to
the PCI interface through the ATU. The core processor always generates Single Address
Cycles on the internal bus. As a PCI master, the ATU is capable of PCI I/O transactions,
PCI memory reads (in case of conventional PCI), memory read DWORD (in case of PCI-
X), PCI memory writes, configuration reads and writes, and DAC cycles. Outbound
memory transactions are always attempted as 64-bit PCI transactions. Outbound
memory write operations are performed as posted operations and outbound memory
read operations are all performed as split read operations.
Outbound transactions use a separate set of queues from inbound transactions.
Outbound write operations have their address entered into the outbound write address
queue (OWADQ) and their data into the outbound write queue (OWQ). Outbound read
transactions, performed as split transactions, use the Outbound Transaction Queue
(OTQ) to store address, and get data returned into the outbound read queue (ORQ).
for details of outbound queue architecture. Outbound
configuration transactions use a special outbound port structure. Refer to
for details.
For outbound write transactions, the ATU is a target on the internal bus and initiator on
the PCI bus. For outbound read transactions, the ATU is a completer on the internal bus
(initially accepts the split read as a target and then provides read data by initiating a
split completion). Internal bus operation is defined in
Chapter 6.0, “System Controller
. ATU specific internal bus operation is defined in
.