TABLE OF CONTENTS Always design a thing by considering it in its next larger context a chair in a room, a room in a house, a house in an environment, an environment in a city plan.
Eliel Saarinen
This chapter introduces the PCI Express architecture, starting off with a system level view. This addresses the basics of a point-to-point architecture, the various types of devices and the methods for information flow through those devices. Next, the chapter drops down one level to further investigate the transaction types, mainly the types of information that can be exchanged and the methods for doing so. Lastly, the chapter drops down one level further to see how a PCI Express device actually goes about building those transactions. PCI Express uses three transaction build layers, the Transaction Layer, the Data Link Layer and the Physical Layer. These architectural build layers are touched upon in this chapter with more details in Chapters 6 through 8.
Whereas PCI is a parallel, multi-drop interface, PCI Express is a serial, point-to-point interface. As such, many of the rules and interactions in PCI are no longer directly applicable to PCI Express. For example, devices no longer need to arbitrate for the right to be the bus driver prior to sending out a transaction. A PCI Express device is always the driver for its transmitter pair(s) and is always the target for its receiver pair(s). Since only one device ever resides at the other end of a PCI Express link, only...
