Energy-Efficient Ethernet (EEE)

The EEE capability combines the IEEE 802.3 Media Access Control (MAC) Sublayer with a family of Physical Layers defined to support operation in the Low Power Idle (LPI) mode. When the LPI mode is enabled, systems on both sides of the link can save power during periods of low link utilization. The key features of EEE are listed below:

• Provides a protocol (The next sections describe the protocols that run on the MII and GMII.) to coordinate transitions to or from a lower level of power consumption.
• Without changing the link status.
• Without dropping or corrupting frames.
• The transition time in to and out of the lower level of power consumption is kept small enough to be transparent to upper layer protocols and applications.

• When the transmit LPI state diagram is in state LPI_ASSERTED, the LPI client requests the PHY to transition to the LPI state by deasserting TX_EN, asserting TX_ER, and setting TXD<3:0> to 0b0001.
• The LPI client requests the PHY to transition out of the LPI state by deasserting TX_ER and TXD

• When the PHY receives signals from the link partner to indicate transition into the low power state, it indicates this to the LPI client by asserting RX_ER and setting RXD<3:0> to 0b0001 while keeping RX_DV deasserted.
• When the PHY receives signals from the link partner to indicate transition out of the low power state, it indicates this to the LPI client by deasserting RX_ER and returning to a normal interframe state.

The GMII has the same LPI mechanism as the MII, except that TXD<7:0> and RXD<7:0> are set to 0x01.

• When PHY or MAC loopback is enabled, the MAC cannot sense the LPI signals it sends. I guess this is because RS maps the xMII to the PLS, not the LPI client, when loopback is enabled.

• IEEE 802.3-2022 Clause 78 - Energy-Efficient Ethernet (EEE)
• IEEE 802.3-2022 Clause 22.2.2 - MII signal functional specifications
• IEEE 802.3-2022 Clause 35.2.2 - GMII signal functional specifications