82583V Datasheet, PDF (157/374 Pages) Intel Corporation – Intel® 82583V GbE Controller

Inline Functions—82583V GbE Controller
7.3.6
Note:
TCP Segmentation Use of Multiple Data Descriptors
TCP segmentation enables a series of data descriptors, each referencing a single
physical address page, to reference a large packet contained in a single virtual-address
buffer.
The only requirement on use of multiple data descriptors for TCP segmentation is as
follows:
• If multiple data descriptors are used to describe the IP/TCP/UDP header section,
each descriptor must describe one or more complete headers; descriptors
referencing only parts of headers are not supported.
It is recommended that the entire header section, as described by the TCP Context
Descriptor HDRLEN field, be coalesced into a single buffer and described using a single
data descriptor. If all the layer headers (L2-L4) are not coalesced into a single buffer,
each buffer must not cross a 4 KB boundary, or be bigger than MAX_READ_REQUEST.
7.3.6.1
Note:
Transmit Checksum Offloading with TCP Segmentation
The 82583V supports checksum offloading as a component of the TCP segmentation
offload feature and as a standalone capability.
The 82583V supports IP and TCP/UDP header options in the checksum computation for
packets that are derived from the TCP segmentation feature.
The 82583V is capable of computing one level of IP header checksum and one TCP/UDP
header and payload checksum. In case of multiple IP headers, the software device
driver has to compute all but one IP header checksum. The 82583V calculates
checksums on the fly on a frame-by-frame basis and inserts the result in the IP/TCP/
UDP headers of each frame. TCP and UDP checksum are a result of performing the
checksum on all bytes of the payload and the pseudo header.
Three specific types of checksum are supported by the hardware in the context of the
TCP Segmentation off load feature:
• IPv4 checksum (IPv6 does not have a checksum)
• TCP checksum
• UDP checksum
Each packet that is sent via the TCP segmentation offload feature optionally includes
the IPv4 checksum and either the TCP or UDP checksum.
All checksum calculations use a 16-bit wide ones complement checksum. The
checksum word is calculated on the outgoing data. The checksum field is written with
the 16-bit ones complement sum of all 16-bit words in the range of CSS to CSE,
including the checksum field itself.
157