PCI Express System Architecture

Memorize Your Identity

General

Whenever a function initiates a transaction as a requester, it must supply its Requester ID in the packet's header. Likewise, when a function initiates a transaction as a Completer, it must supply its Completer ID in the packet header. Both of these IDs are comprised of the Bus Number, Device Number and Function Number.

The function “knows” which function number it is within its device, but how does it know the device it resides within and what bus it resides on?

Each time that the source bridge for a bus initiates a type 0 configuration write transaction (see Figure 21-14 on page 764), it supplies the targeted function with the bus number from its Secondary Bus Number register and the number of the device that ...