PCI Express System Architecture

Type 1 Configuration Request

While in transit to the destination bus, a configuration read or write takes the form of a Type 1 configuration read or write when it is performed on each bus on the way to the destination bus. The only devices that pay attention to a Type 1 configuration read or write are PCI-to-PCI bridges. Upon receipt of a Type 1 configuration read or write request packet, a PCI-to-PCI bridge compares the target bus number in the packet header to the range of buses that reside behind the bridge (as defined by the contents of the bridge's Secondary Bus Number and Subordinate Bus Number configuration registers; see Figure 20-3 on page 728 and Figure 20-4 on page 730).

• If the target bus is the bridge's secondary bus, the packet is ...