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Auxiliary Snapshot
The auxiliary snapshot feature allows you to store a snapshot (timestamp) of the system time based on an
external event. The event is considered to be the rising edge of the sideband signal ptp_aux_ts_trig_i. One
auxiliary snapshot input is available. The depth of the auxiliary snapshot FIFO buffer is 16.
The timestamps taken for any input are stored in a common FIFO buffer. The host can read a register to
know which input’s timestamp is available for reading at the top of this FIFO buffer. The MAC stores these
timestamps in a FIFO buffer. Only 64 bits of the timestamp are stored in the FIFO buffer. When a timestamp
is stored, the MAC indicates this to the host with an interrupt. The value of the timestamp is read through
a FIFO buffer register access.
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IEEE 802.3az Energy Efficient Ethernet
Energy Efficient Ethernet (EEE) standardized by IEEE 802.3-az, version D2.0 is supported by the EMAC. It
is supported by the MAC operating in 10/100/1000 Mbps rates. EEE is only supported when the EMAC is
configured to operate with the RGMII PHY interface operating in full-duplex mode. It does not support
half-duplex mode.
EEE enables the MAC to operate in Low-Power Idle (LPI) mode. Either end point of an Ethernet link can
disable functionality to save power during periods of low link utilization. The MAC controls whether the
system should enter or exit LPI mode and communicates this to the PHY.
†
For details about the
IEEE 802.3az Energy Efficient Ethernet standard
, refer to the IEEE 802.3 Ethernet
Working Group website (www.ieee802.org/3/).
†
Related Information
IEEE 802.3az Energy Efficient Ethernet
LPI Timers
Two timers internal to the EMAC are associated with LPI mode:
• LPI Link Status (LS) Timer
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• LPI TW Timer
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The LPI LS timer counts, in ms, the time expired since the link status is up. This timer is cleared every time
the link goes down and is incremented when the link is up again and the terminal count as programmed by
the software is reached. The PHY interface does not assert the LPI pattern unless the terminal count is
reached. This ensures a minimum time for which no LPI pattern is asserted after a link is established with
the remote station. This period is defined as one second in the IEEE standard 802.3-az, version D2.0. The
LPI LS timer is 10 bits wide. Therefore, the software can program up to 1023 ms.
†
The LPI TW timer counts, in µs, the time expired since the deassertion of LPI. The terminal count of the
timer is the value of resolved transmit TW that is the auto-negotiated time after which the MAC can resume
the normal transmit operation. The MAC supports the LPI TW timer in units of µs. The LPI TW timer is
16 bits wide. Therefore, the software can program up to 65535 µs.
†
The EMAC generates the LPI interrupt when the transmit or receive channel enters or exits the LPI state.
†
Checksum Offload
Communication protocols such as TCP and UDP implement checksum fields, which help determine the
integrity of data transmitted over a network. Because the most widespread use of Ethernet is to encapsulate
TCP and UDP over IP datagrams, the EMAC has a Checksum Offload Engine (COE) to support checksum
Altera Corporation
Ethernet Media Access Controller
17-19
Auxiliary Snapshot
cv_54017
2013.12.30