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PCI Express System Architecture by MindShare, Inc, Ravi Budruk, Don Anderson, Tom Shanley

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Enumerating a System With Multiple Root Complexes

Refer to Figure 21-8 on page 757. In a system with multiple Root Complexes, each Root Complex:

  • Implements the Configuration Address Port and the Configuration Data Port at the same IO addresses (if it's an x86-based system).

  • Implements the Enhanced Configuration Mechanism.

  • Contains a Host/PCI bridge.

  • Implements the Bus Number and Subordinate Bus Number registers at separate addresses known to the configuration software.

Figure 21-8. Peer Root Complexes

In the example illustration, each Root Complex is a member of the chipset and one of them is designated as the bridge to bus 0 (let's call this the ...

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