2 outbound transactions, Section – Intel CONTROLLERS 413808 User Manual
Page 244
Intel
®
413808 and 413812—Address Translation Unit (PCI Express)
Intel
®
413808 and 413812 I/O Controllers in TPER Mode
Developer’s Manual
October 2007
244
Order Number: 317805-001US
3.3.2
Outbound Transactions
Outbound transactions initiated by the 4138xx core processor are directed to the PCI
Express interface through the ATU. As a PCI Express requester, the ATU is capable of
memory, I/O, configuration, and message transactions. Outbound memory transactions
with addresses below 4GB use the short address format (32-bit address). Addresses
above 4GB use the long address format (64-bit).
Outbound transactions use a separate set of queues from inbound transactions.
Outbound write operations have their address entered into the outbound posted header
queue (OPHQ) and their data into the outbound posted data queue (OPDQ). Outbound
read transactions, use the Outbound Non-Posted Queue (ONPQ) to store address, and
get data returned into the Inbound Completion Data Queue (ICPLDQ). Refer to
for details of outbound queue architecture. Outbound configuration
transactions use a special outbound port structure and are enqueue in the ONPQ. Refer
for details.
For outbound write transactions, the ATU is a target on the internal bus and a requester
on the PCI Express Link. 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
Controller (SC) and Internal Bus Bridge”
Note:
For all outbound writes, the byte enables must be contiguous. This means that write
coalescing must be disabled in the Intel XScale
®
microarchitecture for transactions that
target the outbound memory windows.
While Outbound I/O transactions are supported in all configurations, they should only
be used when operating as the root complex. The PCI Express Specification states that
PCI Express Endpoints must not generate I/O requests.