PCI Express System Architecture

Link Training, the First Step in Communication

Link training is one of the first protocols that two agents perform to establish link configuration parameters such as link width, lane polarities, or maximum supported data rate. The following screenshots show the actual data captured for a X4 link training session between the Catalyst PX-4 Exerciser and a PCI Express system board. It should be noted that the link training exercise demonstrated here is based on the 1.0 specification. In the images that follow, several of the repeated packets (all of the idle state) are removed for clarity, but all of the sequences are shown. During the Link Training, the two agents start the communication by sending a low level “ordered set” TS1, and once they each ...