Data Sheet

Interconnects—Ethernet Controller I210
109
3.7.7 Energy Efficient Ethernet (EEE)
Energy Efficient Ethernet (EEE) Low Power Idle (LPI) mode defined in IEEE802.3az optionally enables
power saving by switching off part of the I210 functionality when no data needs to be transmitted or/
and received. The decision as to whether or not the I210 transmit path should enter LPI mode or exit
LPL mode is done according to transmit needs. Information as to whether or not a link partner has
entered LPI mode is detected by the I210 and is used for power saving in the receive circuitry.
When no data needs to be transmitted, a request to enter transmit LPI is issued on the internal xxMII
Tx interface causing the PHY to transmit sleep symbols for a pre-defined period of time followed by a
quite period. During LPI, the PHY periodically transmits refresh symbols that are used by the link
partner to update adaptive filters and timing circuits in order to maintain link integrity. This quiet-
refresh cycle continues until transmitting normal inter-frame encoding on the internal xxMII interface.
The PHY communicates to the link partner the move to active link state by sending wake symbols for a
pre-defined period of time. The PHY then enters a normal operating state where data or idle symbols
are transmitted.
In the receive direction, entering LPI mode is triggered by receiving sleep symbols from the link
partner. This signals that the link partner is about to enter LPI mode. After sending the sleep symbols,
the link partner ceases transmission. When a link partner enters LPI, the PHY indicates assert low
power idle on the internal xxMII RX interface and the I210’s receiver disables certain functionality to
reduce power consumption.
Figure 3-14 shows and Table 3-29 lists the general principles of EEE LPI operation on the Ethernet Link.
Figure 3-14. Energy Efficient Ethernet Operation
Table 3-29. Energy Efficient Ethernet Parameters
Parameter Description
Sleep Time (Ts) Duration PHY sends sleep symbols before going quiet.
Quiet Duration (Tq) Duration PHY remains quiet before it must wake for refresh period.
Refresh Duration (Tr) Duration PHY sends refresh symbols for timing recovery and coefficient synchronization.
PHY Wake Time (Tw_PHY) Minimum duration PHY takes to resume to an active state after decision to wake.
Receive System Wake Time
(Tw_System_rx)
Wait period where no data is expected to be received to give the local receiving system time to
wake up.
Transmit System Wake Time
(Tw_System_tx)
Wait period where no data is transmitted to give the remote receiving system time to wake up.
IDLE
Tq Tr
Tw_PHY
Ts
Quiet Quiet Quiet
Data/
Idle
Refresh Refresh
Wake
Sleep
Low-PowerActive Active
Tw_System
Data/
IDLE
IDLE
Tq Tr
Tw_PHY
Ts
Quiet Quiet Quiet
Data/
Idle
Refresh Refresh
Wake
Sleep
Low-PowerActive Active
Tw_System
Data/
IDLE