Filter
Top Products
Receive and Transmit Description
44 Software Developer’s Manual
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.
3.3.6.1 TCP/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.
RSV
Reserved
Should be programmed to 0b for future compatibility.
STA
TCP/UDP Status field
Provides transmit status indication.
Section 3.3.6.2 provides the bit definition for the TDESC.STA field.
TUCMD
TCP/UDP command field
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.
PAYLEN
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
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.
Transmit
Descriptor Offload
Description