Link Initialization and Training in MAC Layer of PCIe 3.0
The serial protocols like PCI express and USB have evolved over the years to provide very high operating speeds and throughput. This evolution has resulted in their physical layer protocol becoming very complex. One of the most essential processes at physical layer is link initialization and training process. In the PCI Express devices, this process establishes many important tasks such as link width negotiation, link data rate negotiation, bit lock per lane, symbol lock/block alignment per lane, etc. All these functions are accomplished by Link Training & Status State Machine (LTSSM), which observes the stimulus from remote link partner as well as the current state of the link, and responds accordingly.