PHY Functionality and Features

11.6Determining Link State

The PHY and its link partner determine the type of link established through one of three methods:

Auto-Negotiation

Parallel Detection

Forced Operation

Auto-Negotiation is the only method allowed by the 802.3ab standard for establishing a 1000BASE-T link, although forced operation could be used for test purposes. For 10/100 links, any of the three methods can be used. The sections that follow discuss each in greater detail.

Figure 11-2provides an overview of link establishment. First the PHY checks if Auto-Negotiation is enabled. By default, the PHY supports Auto-Negotiation (PHY register 0, bit 12). If not, the PHY forces operation as directed. If Auto-Negotiation is enabled, the PHY begins transmitting Fast Link Pulses (FLPs) and receiving FLPs from its link partner. If FLPs are received by the PHY, Auto-Negotiation proceeds. It also can receive 100BASE-TX MLT3 and 10BASE-T Normal Link Pulses (NLPs). If either MLT3 or NLPs are received, it aborts FLP transmission and immediately brings up the corresponding half-duplex link.

 

 

 

Power-Up, Reset,

 

 

 

 

 

 

 

 

Link Failure

 

 

 

 

 

 

 

 

Start

 

Yes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A/N

 

 

Send FLP

 

 

 

No

 

Enabled

 

 

 

 

 

 

 

?

 

 

 

 

 

 

Speed

 

 

 

 

 

 

 

0 = 10M

0.13

1 = 100M

 

No

 

Yes

 

 

?

 

 

 

Detect

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FLP

 

 

Send NLP

 

 

Send IDLES

 

Parallel

 

Auto

 

 

 

 

 

 

 

 

 

 

 

 

 

Detect

 

Negotiate

 

Detect

 

 

Detect

 

Detect

Yes

100M

 

10Mbps

 

 

10Mbps

 

Half-Duplex

 

 

 

 

IDLES

 

?

 

 

?

 

 

Link

No

 

No

 

 

 

Yes

 

 

Yes

 

 

 

 

 

 

Take

 

Take

No

 

 

Link

Link

 

 

 

 

 

 

Link

 

Link

 

 

 

Down

Up

 

 

 

 

 

 

Down

 

Up

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Detect

 

10M

 

 

 

 

 

 

Yes

Half-Duplex

 

 

 

 

 

 

NLP

 

 

 

 

 

 

 

Link

 

 

 

 

 

 

 

 

Figure 11-2. Overview of Link Establishment

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Software Developer’s Manual

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Intel PCI-X, Intel Gigabit Ethernet Controllers manual Determining Link State, Overview of Link Establishment