82577GBE Datasheet, PDF (6/8 Pages) Intel Corporation – Intel® 82577 GbE PHY Specification Update

82577 Specification Update
1.4.2
Specification Clarifications
1. PHY Does Not Maintain Gigabit Link in Low Power States
Clarification: While operating in power states less than D0 or operating system states other than S0,
the PHY is designed to negotiate to the lowest speed possible, and maintains a link in
those states only at 10 Mb/s or 100 Mb/s. If the PHY is connected to a link partner that is
only capable of gigabit connections, the link is lost in these lower power states. This
limitation is due to power requirements imposed by energy saving initiatives (such as
Energy Star), as the additional power required to maintain gigabit connections might
cause the system to exceed the level needed to meet the specifications.
Impact:
When attached to a port that is limited to gigabit speed connections, the PHY loses link in
low power states, and therefore network functions normally available in those states,
such as Wake on LAN (WoL) or remote management, is not possible in that environment.
2. Activity LED Functionality
Clarification: If a system based on the 82577 is connected to a hub, the Activity LED blinks for all
network traffic present on the hub, not just traffic destined to the local port. Connecting
the system to a switch or router filters out most traffic not addressed to the local port.
1.4.3
Software Clarifications
1. While in TCP Segmentation Offload, Each Buffer is Limited to 64 KB
Problem Description:
Clarification: The 82577 supports 256 KB TCP packets; however, each buffer is limited to 64 KB since
the data length field in the transmit descriptor is only 16 bits. This restriction increases
driver implementation complexity if the operating system passes down a scatter/gather
element greater than 64 KB in length. This can be avoided by limiting the offload size to
64 KB.
Investigation has concluded that the increase in data transfer size does not provide any
noticeable improvements in LAN performance. As a result, Intel network software drivers
limit the data transfer size in all drivers to 64 KB.
Please note that Linux operating systems only support 64 KB data transfers.
For further details about how Intel network software drivers address this issue, refer to
Technical Advisory TA-191.
1.4.4
Documentation Changes
None active.
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