Auto-Negotiation (AN) and Link Training (LT) - 3.2 English

40G/50G High Speed Ethernet Subsystem Product Guide (PG211)

Document ID
PG211
Release Date
2021-10-27
Version
3.2 English

The 40G/50G IP core supports Auto-Negotiation and Link Training. A block diagram of the 40G/50G IP core with AN and LT is illustrated in the following figure.

Figure 1. 40G/50G IP core with Auto-Negotiation and Link Training

The Auto-Negotiation function allows an Ethernet device to advertise the modes of operation it possesses to another device at the remote end of a Backplane Ethernet link and to detect corresponding operational modes the other device might be advertising. The objective of this Auto-Negotiation function is to provide the means to exchange information between two devices and to automatically configure them to take maximum advantage of their abilities. It has the additional objective of supporting a digital signal detect to ensure that the device is attached to a link partner rather than detecting a signal due to crosstalk. When Auto-Negotiation is complete, the ability is reported according to the available modes of operation.

Link Training (LT) is performed after AN if the LT function is supported by both ends of the link. Link training is typically required due to frequency-dependent losses that can occur as digital signals traverse the backplane. The primary function of the LT block included with this IP core is to provide register information and a training sequence over the backplane link which is then analyzed by a receiving circuit (part of the SerDes).

The other function of the LT block is to communicate training feedback from the receiver to the corresponding transmitter so that its pre-emphasis circuit (part of the SerDes) can be adjusted as required. The decision-making algorithm is not part of this IP core.

When AN and LT are complete, the datapath is switched to mission mode (see the above figure).