Definition of Device and Function

Just as in the PCI environment, a device resides on a bus and contains one or more functions (a device containing multiple functions is referred to as a multifunction device). Each of the functions within a multifunction device provides a stand-alone functionality. As an example, one function could be a graphics controller while another might be a network interface.

Just as in PCI, a device may contain up to a maximum of eight functions numbered 0-through-7:

• The one-and-only function implemented in a single-function device must be function 0.

• In a multifunction device, the first function must be function 0, while the remaining functions do not have to be implemented in a sequential manner. In other words, a device could implement functions 0, 2, and 7.

In Figure 19-1 on page 713, Device 0 on Bus 3 is a multifunction device containing two functions, each of which implements its own set of configuration registers.