Receive and Transmit Description

Transmit

Description

Descriptor Offload

 

 

 

RSV

Reserved

Should be programmed to 0b for future compatibility.

 

 

 

 

TCP/UDP Status field

STA

Provides transmit status indication.

 

Section 3.3.6.2 provides the bit definition for the TDESC.STA field.

 

 

 

TCP/UDP command field

TUCMD

The command field provides options that control the checksum offloading, along

with some of the generic descriptor processing functions.

 

 

Section 3.3.6.1 provides the bit definitions for the TDESC.TUCMD field.

 

 

DTYP

Descriptor Type

Set to 0000b for TCP/IP context transmit descriptor type.

 

 

 

 

The packet length field (TDESC.PAYLEN) is the total number of payload bytes for

 

this TCP Segmentation offload context (i.e., the total number of payload bytes that

 

could be distributed across multiply frames after TCP segmentation is performed).

 

Following the fetch of the prototype header, PAYLEN specifies the length of data

 

that is fetched next from data descriptor(s). This field is also used to determine

PAYLEN

when “last-frame” processing needs to be performed. Typically, a new data

descriptor is used to denote the start of the payload data buffer(s), but this is not

 

 

required. PAYLEN specification should not include any header bytes. There is no

 

restriction on the overall PAYLEN specification with respect to the transmit FIFO

 

size, once the MSS and HDRLEN specifications are legal. This field is ignored if

 

TDESC.TSE is not set. Refer to Section 3.5 for details on the TCP Segmentation

 

off-loading feature.

 

 

Notes:

1.A number of the fields are ignored if the TCP Segmentation enable bit (TDESC.TSE) is cleared, denoting that the descriptor does not refer to the TCP segmentation context.

2.Maximum limits for the HDRLEN and MSS fields are dictated by the lengths variables. How- ever, there is a further restriction that for any TCP Segmentation operation, the hardware must be capable of storing a complete section (completely-built frame) in the transmit FIFO prior to transmission. Therefore, the sum of MSS + HDRLEN must be at least 80 bytes less than the allocated size of the transmit FIFO.

3.3.6.1TCP/UDP Offload Transmit Descriptor Command Field

The command field (TDESC.TUCMD) provides options to control the TCP segmentation, along with some of the generic descriptor processing functions.

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Software Developer’s Manual

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Intel PCI-X manual 6.1 TCP/UDP Offload Transmit Descriptor Command Field, Transmit Description, Tucmd, Dtyp, Paylen