EP80579 Datasheet, PDF (1375/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
Four bits are reserved to provide transmit status, although only the DD bit (bit 0) is
valid. The status word will only be written back to host memory in cases where the RS
bit is set in the command field. The DD bit indicates that the descriptor is done and is
written back after the descriptor has been processed.
Figure 37-26.TCP/IP Data Transmit Descriptor Status (TDESC.DSTATUS)
3
2
1
0
Rsvd
DD
Rsvd: Reserved
DD: Descriptor Done
The POPTS field provides a number of options which control the handling of this packet.
This field is ignored except on the first data descriptor of a packet or segmentation
context.
Figure 37-27.TCP/IP Data Transmit Descriptor Packet Options Field (TDESC.POPTS)
7
6
5
4
3
2
1
0
Rsvd
TXSM IXSM
Rsvd: Reserved
TXSM: Insert TCP/UDP Checksum
IXSM: Insert IP Checksum
IXSM and TXSM are used to control insertion of the IP and TCP/UDP checksums,
respectively. If the corresponding bit is not set, whatever value software has placed
into the checksum field of the packet data will be placed on the wire. These bits are
only valid in the first data descriptor for a given packet or TCP segmentation context.
The VLAN field is used to provide the 802.1q tagging information. The special field is
ignored if the VLE bit is 0.
Figure 37-28.TCP/IP Data Transmit Descriptor Special Field (TDESC.VLAN)
15
13 12 11
0
PRI
CFI
VLAN ID
37.5.6.6
Transmit Descriptor Structure
A pair of hardware registers maintains the transmit descriptor ring in the host memory.
New descriptors are added to the queue by software by writing descriptors into the
circular buffer memory region and moving the tail pointer associated with that queue.
The tail pointer points one entry beyond the last hardware owned descriptor.
Transmission continues up to the descriptor where head equals tail at which point the
queue is empty.
Descriptors passed to hardware should not be manipulated by software until the head
pointer has advanced past them.
The transmit descriptor ring structure is shown in Figure 37-29. Shaded boxes
represent descriptors that have been transmitted but not yet reclaimed by software.
Reclaiming involves freeing up buffers associated with the descriptors.
August 2009
Order Number: 320066-003US
Intel^® EP80579 Integrated Processor Product Line Datasheet
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