February, 2007
Software Configuration and Routing
7.2.1
Software Configuration and Routing
Configuration requests must be routed from the Host, through the PEX 8532’s upstream port. All Type 0
Configuration requests access the PEX 8532’s upstream port Configuration registers.
The upstream port’s PCI-to-PCI bridge forwards Type 1 Configuration requests from its upstream
interface to its downstream interface. The Secondary Bus Number of the upstream port matches the
Primary Bus Number of every downstream port. If the Bus Number value encoded in the Configuration
Request matches the upstream port’s Secondary Bus Number, the Configuration request is targeting a
downstream port’s registers, and therefore the upstream port converts the Type 1 Configuration request
to a Type 0 Configuration request. To access the PCI-to-PCI bridge registers of a specific downstream
port, the Device Number value encoded in this Configuration Request (which the upstream port
converted to Type 0) must match the Device Number (Port Number) of the downstream port (the Device
Number of a downstream port is always the same value as the designated Port number). If the Bus
Number value encoded in the Configuration request matches the upstream port’s Secondary Bus
Number, the Configuration Request is targeting a downstream port’s registers, and therefore, the
upstream port converts the Type 1 Configuration Request to a Type 0 Configuration Request. To access
the PCI-to-PCI bridge registers of a specific downstream port, the Type 1 Configuration request Bus
Number value must match the upstream port’s Secondary Bus Number, and the Device Number must
match the enabled downstream port’s Device Number. All other Device Numbers are non-existent
devices, and the Configuration request terminates with an Unsupported Request (UR) completion.
To configure additional devices in the PCI hierarchy, the switch downstream ports must have their
Secondary and Subordinate Bus Numbers set. Any match on a downstream port PCI-to-PCI bridge’s
Secondary Bus Numbers results in the PEX 8532 converting the incoming Type 1 Configuration request
to an outgoing Type 0 Configuration request, and the Device Number must be 0.
Figure 7-1. PEX 8532 System Configuration Propagation
Configuration
Propagation
Upstream
Port
Virtual PCI Bus
Upstream
P-P Bridge
P-P
Downstream
P-P Bridges
P-P
P-P
P-P
P-P
P-P
P-P
P-P
Downstream
Ports
Upstream Station
Downstream Station
ExpressLane PEX 8532AA/BA/BB/BC 8-Port/32-Lane Versatile PCI Express Switch Data Book
Copyright © 2007 by PLX Technology, Inc. All Rights Reserved – Version 1.6
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