EP80579 Datasheet, PDF (1401/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
Figure 37-48.TCI Bit Ordering
Octet 1
UP
CFI
VID
Octet 2
37.5.9.1
Transmitting and Receiving 802.1q Packets
Since the 802.1q tag is only four bytes, adding and stripping of tags could be done
completely in software. (i.e., For transmits, software inserts the tag into packet data
before it builds the transmit descriptor list, and for receives, software strips the 4 byte
tag from the packet data before delivering the packet to upper layer software.)
However, because adding and stripping of tags in software results in more over-head
for the host, the GbE has additional capabilities to add and strip tags in hardware.
37.5.9.1.1 Adding 802.1q Tags on Transmits
Software may command the GbE to insert an 802.1q VLAN tag on a per packet basis. If
CTRL.VME is set to 1, and the VLE bit in the transmit descriptor is set to 1, then the
EP80579’s GbE will insert a VLAN tag into the packet that it transmits over the wire.
The Tag Protocol Identifier (TPID) field of the 802.1q tag comes from the VET register,
and the Tag Control Information (TCI) of the 802.1q tag comes from the special field
Figure 37-9, “Special Descriptor Field Layout” on page 1358of the transmit descriptor.
Refer to Table 37-2, “VLAN Tag Insertion Decision Table when VLAN Mode Enabled
(CTRL.VME=1)” on page 1368, for more information regarding hardware insertion of
tags for transmits.
Similarly, software can instruct the GbE to insert an 802.1q VLAN tag for secure
packets. Software gives the command “transmit with VLAN” to the security subsystem
to instruct hardware that a VLAN tag should be inserted before the packet is sent on
the wire. The Tag Protocol Identifier (TPID) field of the 802.1q tag comes from the VET
register, and the Tag Control Information (TCI) of the 802.1q tag is specified in the
“transmit with VLAN” command itself.
37.5.9.1.2 Stripping 802.1q Tags on Receives
Software may instruct the GbE to strip 802.1q VLAN tags from received packets. If the
CTRL.VME bit is set to 1, and the incoming packet is an 802.1q VLAN packet (i.e. it's
Ethernet Type field matched the VET register), then the EP80579’s GbE strips the 4
byte VLAN tag from the packet, and stores the TCI in the Special field (see Figure 37-9,
“Special Descriptor Field Layout” on page 1358) of the receive descriptor.
The EP80579’s GbE also sets the VP bit in the receive descriptor to indicate that the
packet had a VLAN tag that was stripped. If the CTRL.VME bit is not set, the 802.1Q
packets can still be received if they pass the receive filter, but the VLAN tag will not be
stripped and the VP bit will not be set. Refer to Table 37-5 on page 1402 for more
information regarding receive packet filtering.
37.5.9.2
802.1q VLAN Packet Filtering
VLAN filtering is enabled by setting the RCTL.VFE bit to 1. If enabled, hardware
compares the type field of the incoming packet to a 16 bit field in the VLAN EtherType
Register (VET). If the VLAN type field in the incoming packet matches the VET register,
the packet is then compared against the VLAN Filter Table Array for acceptance.
August 2009
Order Number: 320066-003US
Intel^® EP80579 Integrated Processor Product Line Datasheet
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