Datasheet

Intel
®
Xeon
®
Processor C5500/C3500 Series
February 2010 Datasheet, Volume 1
Order Number: 323103-001 129
Interfaces
2.6.12.2 Attributes
PCI Express supports two attribute hints described in Table 74. This table describes
how these attribute fields are populated for requests and completions.
2.6.12.3 Traffic Class
The IIO does not optimize based on traffic class. IIO can receive a packet with TC != 0
and treat the packet as if it were TC = 0 from an ordering perspective. IIO forwards the
TC filled as is on p2p requests and also returns the TC field from the original request on
the completion packet sent back to the device.
2.6.13 Completer ID
The CompleterID field is used in PCI Express completion packets to identify the
completer of the transaction. The CompleterID comprises three sub-fields described in
Table 75.
2.6.14 Miscellaneous
2.6.14.1 Number of Outbound Non-posted Requests
The x4 PCI Express interface supports up to 16 outstanding non-posted transactions
outbound comprising transactions issued by the processors. x8 supports 32 and x16
supports 64.
2.6.14.2 MSIs Generated from Root Ports and Locks
Once lock has been established on the coherent interface, IIO cannot send any
requests on the coherent interface, and this includes MSI transactions generated from
the root port of the PCIe port that is locked. This requirement imposes that the MSI’s
from the root port should not block (locked read) completions from the PCI Express
port moving to the coherent interface.
Table 74. PCI Express Attribute Handling
Attribute Definition IIO as Requester IIO as Completer
Relaxed
Ordering
Allows the system to relax some of the
standard PCI ordering rules.
This bit is not
applicable and set to
zero for transactions
generated on PCIe
on behalf of a Intel
®
QPI request. On
peer-to-peer
requests, IIO
forwards this
attribute as-is.
This field is preserved
from the request and
copies it into the
completion.
Snoop Not
Required
This attribute is set when an I/O device
controls coherency through software
mechanisms. This attribute is an
optimization designed to preserve
processor snoop bandwidth.
Table 75. PCI Express CompleterID Handling
Field Definition IIO as Completer
Bus Number
Specifies the bus number that the
completer resides on.
The IIO fills this field in with its internal Bus
Number that the PCI Express cluster resides
on.
Device Number
Specifies the device number of the
completer.
Device number of the root port sending the
completion back to PCIe.
Function
Number
Specifies the function number of the
completer.
0