82583V Datasheet, PDF (152/374 Pages) Intel Corporation – Intel® 82583V GbE Controller

82583V GbE Controller—Inline Functions
Table 43.
Note:
Note:
Note:
Although the transmit interrupt might be delayed, the descriptor write-back requested
by setting the RS bit is performed without delay unless descriptor write-back bursting is
enabled.
VLE indicates that the packet is a VLAN packet (for example, that the hardware should
add the VLAN Ether type and an 802.1Q VLAN tag to the TCP message).
VLAN Tag Insertion Decision Table
VLE
0
1
Action
Send generic Ethernet packet. IFCS controls insertion of FCS in normal Ethernet
packets.
Send 802.1Q packet; the Ethernet Type field comes from the VET register and the
VLAN data comes from the special field of the TX descriptor; hardware always
appends the FCS/CRC.
If the VLE bit is set to enable VLAN tag insertion, the CTRL.VME bit should also be set.
The DEXT bit identifies this descriptor as one of the extended descriptor types and
must be set to 1b.
When the RS bit is set, the hardware writes back the DD bit once the DMA fetch
completes.
Descriptors with the null address (0), or zero length, transfer no data. If they have the
RS bit in the command byte set, then the DD field in the status word is written when
hardware processes them. Hardware only sets the DD bit for descriptors with RS set.
Software can set the RS bit in each descriptor or, more likely, in specific descriptors
such as the last descriptor of each packet.
TSE indicates that this descriptor is part of the current TCP segmentation context. If
this bit is not set, the descriptor is part of the normal non-segmentation context.
IFCS controls insertion of the Ethernet CRC. The packet FCS covers the TCP/IP headers.
Therefore, when using the TCP segmentation offload, software must also use the FCS
insertion.
The VLE, IFCS, and VLAN fields are only valid in certain descriptors. If TSE is enabled,
the VLE, IFCS, and VLAN fields are only valid in the first data descriptor of the TCP
segmentation context. If TSE is not enabled, then these fields are only valid in the last
descriptor of the given packet (qualified by the EOP bit).
EOP when set, indicates the last descriptor making up the packet.
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