82583V Datasheet, PDF (142/374 Pages) Intel Corporation – Intel® 82583V GbE Controller

82583V GbE Controller—Inline Functions
7.2.9
Transmit Descriptor Formats
The original descriptor is referred to as the legacy descriptor and is described in
section 7.2.9.1. The two new descriptor types are collectively referred to as extended
descriptors. One of the new descriptor types is quite similar to the legacy descriptor in
that it points to a block of packet data. This descriptor type is called the extended data
descriptor. The other new descriptor type is fundamentally different as it does not point
to packet data. This descriptor type is called the context descriptor. It only contains
control information, which is loaded into registers of the 82583V, and affects the
processing of future packets. The following paragraphs describe the three descriptor
formats.
The new descriptor types are specified by setting the TDESC.DEXT bit to 1b. If this bit
is set, the TDESC.DTYP field is examined to determine the descriptor type (extended
data or context). Figure 35 shows the context descriptor generic layout. Figure 37
shows the data descriptor generic layout.
7.2.9.1
Legacy Transmit Descriptor Format
63
0
8
VLAN
4847 40 39 3635 3231 2423
16 15
0
Buffer Address [63:0]
CSS ExtCMD STA CMD
CSO
Length
Figure 34.
VLAN
Checksum
Start
Status
15 13 12 11
08
03
10 3 2 1 0
PRI CFI VLAN
CSS ExtCMD TS Rsv Res Res DD
Command
76543
IDE VLE DEXT RSV RS
Checksum
Offset
Length
2 1 08
0 15
IC IFCS EOP ^CSO
LENGTH
Legacy Transmit Descriptor Format
The legacy Tx descriptor is defined by setting the DEXT bit in the command field to 0b.
The legacy Tx descriptor format is shown in Figure 34.
7.2.9.1.1
Buffer Address
The buffer address (TDESC.Buffer Address) specifies the location (address) in main
memory of the data to be fetched.
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