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Receive and Transmit Description
Software Developer’s Manual 47
Table 3-17. Transmit Descriptor (TDESC) Layout – (Type = 0001b)
0 Address [63:0]
8 Special POPTS RSV STA DCMD DTYP DTALEN
0 63 48 47 40 39 36 35 32 31 24 23 20 19 0
Transmit Descriptor Description
Address
Data buffer address
Address of the data buffer in the host memory which contains a portion of the
transmit packet.
DTALEN
Data Length Field
Total length of the data pointed to by this descriptor, in bytes.
For data descriptors not associated with a TCP Segmentation operation
(TDESC.TSE not set), the descriptor lengths are subject to the same restrictions
specified for legacy descriptors (the sum of the lengths of the data descriptors
comprising a single packet must be at least 80 bytes less than the allocated size
of the transmit FIFO.)
DTYP
Data Type
Set to 0001b to identify this descriptor as a TCP/IP data descriptor.
DCMD
Descriptor Command Field
Provides options that control some of the generic descriptor processing
features. Refer to Section 3.3.7.1 for bit definitions of the DCMD field.
STA
TCP/IP Status field
Provides transmit status indication.
Section 3.3.7.2 provides the bit definition for the TDESC.STA field.
RSV
Reserved
Set to 0b for future compatibility.
POPTS
Packet Option 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.
Section 3.3.7.3 provides the bit definition for the TDESC.POPTS field.
Special
Special field
The Special field is used to provide 802.1q tagging information.
This field is only valid in the last descriptor of the given packet (qualified by the
EOP bit).