Data Sheet

Ethernet Controller I210 —Inline Functions

308

7.2.4.7 TCP/UDP/IP Headers Update

IP/TCP or IP/UDP header is updated for each outgoing frame based on the IP/TCP header prototype

which hardware DMA's from the first descriptor(s). The checksum fields and other header information

are later updated on a frame-by-frame basis. The updating process is performed concurrently with the

packet data fetch.

The following sections define what fields are modified by hardware during the TCP Segmentation

process by the I210.

Note: Placing incorrect values in the Context descriptors might cause failure of Large Send. The

indication of Large Send failure can be checked in the TSCTC statistics register.

7.2.4.7.1 TCP/UDP/IP Headers for the First Frames

The hardware makes the following changes to the headers of the first packet that is derived from each

TCP segmentation context.

MAC Header (for SNAP)

• Type/Len field = MSS + MACLEN + IPLEN + L4LEN - 14 - 4 (if VLAN added by Software)

IPv4 Header

• IP Identification: Value in the IPv4 header of the prototype header in the packet data itself

•IP Total Length = MSS + L4LEN + IPLEN

•IP Checksum

IPv6 Header

•Payload Length = MSS + L4LEN + IPV6_HDR_extension

TCP Header

• Sequence Number: The value is the Sequence Number of the first TCP byte in this frame.

• The flag values of the first frame are set by ANDing the flag word in the pseudo header with the

DTXTCPFLGL.TCP_flg_first_seg register field. The default value of the

DTXTCPFLGL.TCP_flg_first_seg are set so that the FIN flag and the PSH flag are cleared in the first

frame.

• TCP Checksum

UDP Header

• UDP Length = MSS + L4LEN

• UDP Checksum

Yes Yes TCP segment or UDP datagram with checksum off-load

No No Non-IP packet or checksum not offloaded

TSO Yes Yes For TSO, checksum off-load must be done

1. IPV6_HDR_extension is calculated as IPLEN - 40 bytes.

Table 7-44. Conditions for Checksum Offloading