Transition Networks
SGFEB 10/100/1000 Bridging Media Converter User Guide
33601 Rev. D
Page 16 of 25
Energy Efficient Ethernet (EEE)
Energy efficient Ethernet can significantly reduce the power consumption of the device over a period of
time especially when there is a large amount of idle signals on the copper port. IEEE standard 802.3az
which implements a Low Power Idle mode on copper interfaces with internal PHYs. SGFEB TP Ports
have the EEE Low Power Idle mode enabled. Note that the Link LED remains lit when in low power
mode. You can disable the 802.3az EEE function with a 2-pin header and a jumper (J13) on the board.
The SGFEB ships with EEE enabled; Jumper J13 has the jumper (shorting plug) uninstalled. Contact TN
Tech Support to obtain the two-position jumper TN6907 if you want to disable EEE.
The amount of delay experienced while waiting for the copper interfaces to wake up and come out of low
power idle mode is determined by the speed of the port:
Delay = ASSERT TIME + WAKE TIME
For 1000 Base, delay = 0 + 17us = 17us. For 100 Base, delay = 0 + 30us = 30us.
EEE Low Power Idle mode requires the copper port to advertise via the auto negotiation registers the
ability to support EEE for both 1000Base-T and 100Base-T. Both local and remote ports must indicate
they can support low power idle mode before the port can initiate a low power idle state.
During Auto –Negotiation the Port EEE capabilities are exchanged using the next page process to
establish the speed and duplex information. Timer information with regards to tx_idle, assert and wake
cycles are set in SGFEB registers by the CPU. When a port egress queue remains empty for a specific
period of time set by the EEE TX_IDLE Timer register, then a low power state can be entered. The
default setting for the TX_IDLE is 2 milliseconds.
After the TX_IDLE time the PHY will start the assert timer. The Assert timer will require the SGFEB to wait
until the assert timer is zero before a wake up request can be processed. Currently the default Assert
timer is set to 0, giving the PHY the ability to immediately start processing a request to leave the low
power idle state. The PHY then enters low power idle mode. This mode is defined by a 22.35mili-seconds
quiet period followed by a 210us refresh pulse. Then once a port sends a packet and the egress queue is
no longer empty a wake up period is needed for the PHY to return to full operation. The default wake
times are set to 17 micro-seconds for 1000Base and 30 micro-seconds for 100Base. During this wakeup
time the packet will continue to buffer in the egress queue until the wake up timer has completed at this
point port traffic will begin to flow as normal.
The SGFEB
can also support a reduced power mode for 10Base-T in which it modifies the copper media
transmit waveform to achieve power consumption savings.
