EP80579 Datasheet, PDF (1388/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
Figure 37-44.UDP Pseudo Header Diagram for IPv4
0
Zero
31
IP Source Address
IP Destination Address
Protocol ID
UDP Length
Figure 37-45.UDP Pseudo-Header Diagram for IPv6
0
31
IP Source Address
IP Destination Address
Note:
37.5.7.8
Note:
Upper Layer Packet Length
Zero
Next Header
The IP Destination Address is the final destination of the packet. Therefore, if a routing
header is used, the last address in the route list is used in this calculation. The upper-
layer packet length is the length of the UDP header and UDP payload.
Unlike the TCP checksum, the UDP checksum is optional. Software must set the TXSM
bit in the TCP/IP Context Transmit Descriptor to indicate that a UDP checksum should
be inserted. Hardware will not update the UDP checksum unless the TXSM bit is set.
Transmit Checksum Off loading with TCP Segmentation
The GbE supports checksum off-loading as a component of the TCP Segmentation off
load feature and as a standalone capability. Refer to “TCP/IP Context Transmit
Descriptor Format” on page 1369 for details on the interface for controlling the
checksum off-loading feature. This section describes the feature as it relates to TCP
Segmentation.
The GbE supports IP and TCP/UDP header options in the checksum computation for
packets that are derived from the TCP Segmentation feature.
The GbE is capable of computing one level of IP header checksum and one TCP/UDP
header and payload checksum. In the case of multiple IP headers, the driver will have
to compute all but one IP header checksum. The GbE 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, and UDP checksum.
Each packet that is sent via the TCP segmentation off load feature optionally includes
the IPv4 checksum and either the TCP or UDP checksum.
All checksum calculations use a 16-bit wide one's complement checksum calculated of
all 16-bit words in the range of CSS to CSE, including the checksum field itself. The
checksum field is written with this hardware computed value.
Intel^® EP80579 Integrated Processor Product Line Datasheet
1388
August 2009
Order Number: 320066-003US