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

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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