Filter
Top Products
Link Criteria — Intel
®
82575EB Gigabit Ethernet Controller
324632-003 Intel
®
82575EB Gigabit Ethernet Controller
Revision: 2.1 Software Developer’s Manual and EEPROM Guide
January 2011 267
11.3 Link Criteria
Once the link state is determined—via Auto-Negotiation, parallel detection or forced operation— the
PHY and its link partner bring up the link.
11.3.1 1000BASE-T
For 1000BASE-T links, the PHY and its link partner enter a training phase. They exchange idle symbols
and use the information gained to set their adaptive filter coefficients.
Either side indicates completion of the training phase to its link partner by changing the encoding of the
idle symbols it transmits. When both sides so indicate, the link is up. Each side continues sending idle
symbols whenever it has no data to transmit. The link is maintained as long as valid idle or data
symbols are received.
11.3.2 100BASE-TX
For 100BASE-TX links, the PHY and its link partner immediately begin transmitting idle symbols. Each
side continues sending idle symbols whenever it has no data to transmit. The link is maintained as long
as valid idle symbols or data is received.
In 100 Mb/s mode, the PHY establishes a link whenever the scrambler becomes locked and remains
locked. Link will remain up unless the descrambler receives idles at less than a specified rate.
11.3.3 10BASE-T
For 10BASE-T links, the PHY and its link partner begin exchanging Normal Link Pulses (NLPs). The PHY
transmits an NLP every 16 ms, and expects to receive one every 10 to 20 ms. The link is maintained as
long as normal link pulses are received.
11.4 Link Enhancements
The PHY offers two enhanced link functions, each of which are discussed in the sections that follow:
• SmartSpeed
• Flow Control
11.4.1 SmartSpeed
SmartSpeed is an enhancement to auto-negotiation that enables the PHY to react intelligently to
network conditions that prohibit establishment of a 1000BASE-T link, such as cable problems. Such
problems might allow auto-negotiation to complete, but then inhibit completion of the training phase.
Normally, if a 1000BASE-T link fails, the PHY returns to the auto-negotiation state with the same speed
settings indefinitely. With SmartSpeed enabled, after a configurable number (1-5, PHY Register 27d bits
8:6) of failed attempts, the PHY automatically downgrades the highest ability it advertises to the next