PCIe learning - how to make PCIe bus compatible with PCI bus in software (7)

The previous article said many times ,PCIe The bus is forward compatible in software PCI Bus . therefore ,PCIe The bus completely inherits PCI Configuration space in the bus （Configuration Header） The concept of . stay PCIe There are also two types in the bus Header,Header0 and Header1, Represents non bridge and bridge equipment respectively , This is related to PCI The bus is completely consistent . stay PCIe In the bus , Non bridge equipment, that is Endpoint. As shown in the figure below ：

As shown in the figure , Compare with the previous Introduction PCI Of Header You can find ：PCIe Of Header Basically with PCI Of Header It's consistent , Only a little difference . But these differences do not affect PCIe Yes PCI The compatibility of （ also PCIe To PCI The bridge treats it ）.

One thing to note is that ,Root Complex（RC or Root） and Switch It's all new PCIe The concept of , Every port in their structure （Port） Can correspond to PCI In the bus PCI-to-PCI The concept of bridge . in other words , every last RC and Switch There are usually several similar to PCI-to-PCI Bridge thing . As shown in the following two figures ：

I've talked about ,PCIe Bus is a kind of point-to-point （Point-to-Point） Bus of , If you need to connect a large number of devices , It takes a lot of Switch For Topology , This will undoubtedly greatly increase the power consumption and design cost of the system . In ordinary PC Or in a small computer system , Don't connect many PCIe equipment , therefore Switch It doesn't seem so necessary . A typical server PCIe The topology of the bus system is shown in the figure below ：

Typical PC Of PCIe The topology of the bus system is shown in the figure below ：