An Endpoint Embedded in a Switch or Root Complex

The spec contains the following two statements:

• "Endpoint devices (represented by Type 00h Configuration Space headers) may not appear to configuration software on the switch's internal bus as peers of the virtual PCI-to-PCI Bridges representing the Switch Downstream Ports."

• "Switch Downstream Ports are PCI-PCI Bridges bridging from the internal bus to buses representing the Downstream PCI Express Links from a PCI Express Switch. Only the PCI-PCI Bridges representing the Switch Downstream Ports may appear on the internal bus. Endpoints, represented by Type 0 configuration space headers, may not appear on the internal bus."

Nothing in this text forbids the implementation of an Endpoint device within a switch. In addition, nothing in the spec forbids the implementation of an Endpoint device within a Root Complex. Figure 21-12 on page 762 and Figure 21-13 on page 763 illustrate examples of these design cases.