PCI Express System Architecture

How To Differentiate a PCI-to-PCI Bridge From a Non-Bridge Function

Refer to Figure 19-3 on page 717 and Figure 19-4 on page 719. The lower 7 bits of the Header Type register identifies the basic category of the function:

• 0 = the function is not a bridge.

• 1 = the function is a PCI-to-PCI bridge (aka P2P) interconnecting two buses.

• 2 = the function is a CardBus bridge.

Figure 19-4. Header Type Register

In Figure 19-1 on page 713, the Header Type field in each of the Virtual P2Ps would return a value of 1, as would the PCI Express-to-PCI bridge (Bus 8, Device 0), while those in the following Endpoint functions would return 0:

• Bus 3, Device 0.

• Bus 4, ...