Data Sheet

Ethernet Controller I210 —System Manageability
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The maximum size of the received packet is limited by the I210 hardware to 1536 bytes. Packets larger
then 1536 bytes are silently discarded. Any packet smaller than 1536 bytes is processed.
10.5.7 Transmit TCO Flow
The I210 is used as the channel for transmitting packets from the external MC to the network link. The
network packet is transferred from the MC over the SMBus and then, when fully received by the I210,
is transmitted over the network link.
The I210 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 Flash and cannot be changed by the
MC.
The minimum packet length defined by the 802.3 spec is 64 bytes. The I210 pads packets that are less
than 64 bytes to meet the specification requirements (there is no need for the external MC to pad
packets less than 64 bytes). If the packet sent by the MC is larger than 1536 bytes, the I210 silently
discards the packet. The minimal packet size that the I210 can handle is 17 bytes.
The I210 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 or VLAN) must be calculated and inserted by the MC (the
I210 does not change any field in the transmitted packet, other than adding padding and CRC bytes).
If the network link is down when the I210 has received the last fragment of the packet from the MC, 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 the I210 waits for the last fragment to end to see whether the
network link is up again.
10.5.7.1 Transmit Errors in Sequence Handling
Once a packet is transferred over the SMBus from the MC to the I210, the F and L flags should follow
specific rules. The F flag defines the first fragment of the packet; the L flag that the transaction contains
the last fragment of the packet. Table 1 0-9 lists the different flag options in transmit packet
transactions.
Note: Since every other Block Write command in TCO protocol has both F and L flags on, they cause
flushing any pending transmit fragments that were previously received. When running the
TCO transmit flow, no other Block Write transactions are allowed in between the fragments.
Table 10-9. Flag Options During Transmit Packet Transactions
Previous Current Action/Notes
Last First Accept both.
Last Not First
Error for the current transaction. Current transaction is discarded and an abort status is
asserted.
Not Last First
Error in previous transaction. Previous transaction (until previous First) is discarded. Current
packet is processed.
No abort status is asserted.
Not Last Not First Process the current transaction.