82598EB Datasheet, PDF (438/596 Pages) Intel Corporation – Intel® 82598EB 10 Gigabit Ethernet Controller Datasheet

Intel^® 82598EB 10 GbE Controller - Transmit TCO Flow
The maximum size of the received packet is limited by hardware to 1536 bytes. Packets larger then
1536 bytes are silently discarded. Any packet smaller than 1536 bytes is processed.
5.3.8 Transmit TCO Flow
The 82598EB is used as the channel for transmitting packets from the external BMC to the network link.
The network packet is transferred from the BMC over the SMBus and then, when fully received by the
82598EB, is transmitted over the network link.
In dual-address mode, each SMBus address is connected to a different LAN port. When a packet is
received during a SMBus transaction using SMBus address #0, it is transmitted to the network using
LAN port #0 and is transmitted through LAN port #1, if received on SMBus address #1. In single
address mode, the transmitted port is chosen according to the fail-over algorithm.
The 82598EB supports packets up to an Ethernet packet length of 1536 bytes. Since SMBus
transactions can only be up to 240 bytes in length, packets might need to be transferred over the
SMBus in more than one fragment. This is achieved using the F and L bits in the command number of
the transmit TCO packet Block Write command. When the F bit is set, it is the first fragment of the
packet. When the L bit is set, it is the last fragment of the packet. When both bits are set, the entire
packet is in one fragment. The packet is sent over the network link, only after all its fragments are
received correctly over the SMBus. The maximum SMBus fragment size is defined within the EEPROM
and cannot be changed by the BMC.
If the packet sent by the BMC is larger than 1536 bytes, than the packet is silently discarded by the
82598EB. The minimum packet length defined by the 802.3 spec is 64 bytes. The 82598EB pads
packets that are less than 64 bytes to meet the specification requirements (there is no need for the
external BMC to pad packets less than 64 bytes). If the packet sent by the BMC is larger than 1536
bytes the 82598EB silently discards the packet.
The The 82598EB calculates the L2 CRC on the transmitted packet and adds its four bytes at the end of
the packet. Any other packet field (such as XSUM) must be calculated and inserted by the BMC (the
82598EB does not change any field in the transmitted packet, other than adding padding and CRC
bytes).
If the network link is down when 82598EB has received the last fragment of the packet from the BMC,
it silently discards the packet. Note that any link down event during the transfer of any packet over the
SMBus does not stop the operation since 82598EB waits for the last fragment to end to see whether the
network link is up again.
5.3.8.1 Transmit Errors in Sequence Handling
Once a packet is transferred over the SMBus from the BMC to 82598EB, the F and L flags should follow
specific rules. The F flag defines that this is the first fragment of the packet; the L flag defines that the
transaction contains the last fragment of the packet.
Flag options during transmit packet transactions lists the different flag options in transmit packet
transactions:
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