Receive and Transmit Description

Table 3-17. Transmit Descriptor (TDESC) Layout – (Type = 0001b)

0

8

Address [63:0]

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Data Length Field

 

 

 

 

 

 

 

Total length of the data pointed to by this descriptor, in bytes.

 

DTALEN

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.

 

 

 

 

 

 

 

 

 

 

 

TCP/IP Status field

 

 

 

 

 

STA

 

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Packet Option Field

 

 

 

 

 

POPTS

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 field

 

 

 

 

 

 

Special

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).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Software Developer’s Manual

47

Page 61
Image 61
Intel PCI-X manual Transmit Descriptor Tdesc Layout Type = 0001b, Popts RSV STA Dcmd Dtyp Dtalen