82598EB Datasheet, PDF (271/596 Pages) Intel Corporation – Intel® 82598EB 10 Gigabit Ethernet Controller Datasheet

Intel^® 82598EB 10 GbE Controller - Transmit Functionality
TUCMD.L4T=1b specifies that the packet type is TCP, and that the 16-bit TCP header checksum should
be inserted at byte offset MACLEN+IPLEN+16. TUCMD.L4T=0 indicates that the packet is UDP and that
the 16-bit checksum should be inserted starting at byte offset MACLEN+IPLEN+6.
MACLEN+IPLEN specifies the byte offset from the start of the transferred data to the first byte to be
included in the checksum, the start of the TCP header. The minimal allowed value for this sum is 18/28
for UDP or TCP, respectively. Note that the maximum value for these fields is 127 for MACLEN and 511
for IPLEN. This is adequate for typical applications.
Note: The MACLEN+IPLEN value needs to be less than the total DMA length for a packet. If this is
not the case, the results are unpredictable.
The TCP/UDP checksum always continues to the last byte of the DMA data.
Note:
For non-TSO, software still needs to calculate a full checksum for the TCP/UDP pseudo-
header. This checksum of the pseudo-header should be placed in the packet data buffer at the
appropriate offset for the checksum calculation.
3.5.3.6 Multiple Transmit Queues
The number of transmit queues is increased to 32 to support multiple CPUs and virtual systems.
3.5.3.6.1 Description
In transmission, each processor sets a queue in the host memory.
Figure 3-38. Multiple Queues in Transmit
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