Realtek RTL8169 Manual page 51

Large-Send Task Offload Tx Descriptor Format (before transmitting, OWN=1, LGSEN=1, Tx command mode 0)
bit
31 30 29 28 27 26
O E F L L
W O S S G
N R S
= E
1 N
=
1
RSVD
TX_BUFFER_ADDRESS_LOW
TX_BUFFER_ADDRESS_HIGH
Offset# Bit#
0 31
0 30
0 29
0 28
0 27
0 26:16
0 15:0
4 31:18
cont...
2002/03/27
Large-Send MSS value
(11 bits)
Symbol
OWN
EOR
FS
LS
LGSEN
MSS
Frame_Length
RSVD
16 15
Frame_Length
T R
A S
VIDL
G V
C D
Ownership: This bit, when set, indicates that the descriptor is owned
by THE NIC, and the data relative to this descriptor is ready to be
transmitted. When cleared, it indicates that the descriptor is owned by
host system. The NIC clears this bit when the relative buffer data is
transmitted. In this case, OWN=1.
End of Descriptor Ring: This bit, when set, indicates that this is the
last descriptor in descriptor ring. When the NIC's internal transmit
pointer reaches here, the pointer will return to the first descriptor of the
descriptor ring after transmitting the data relative to this descriptor.
First Segment Descriptor: This bit, when set, indicates that this is the
first descriptor of a Tx packet, and that this descriptor is pointing to the
first segment of the packet.
Last Segment Descriptor: This bit, when set, indicates that this is the
last descriptor of a Tx packet, and that this descriptor is pointing to the
last segment of the packet.
Large Send: A command bit; TCP/IP Large send operation enable. The
driver sets this bit to ask the NIC to offload the Large send operation. In
this case, LGSEN=1.
Maximum Segmentation Size: An 11-bit long command field, the
driver passes large send MSS to the NIC through this field.
Transmit Drame Length: This field indicates the length in TX buffer,
in byte, to be transmitted
Reserved
51
8 7 6 5 4 3 2
VLAN_TAG
PRIO C VIDH
FI
Description
RTL8169
1 0
Offset 0
Offset 4
Offset 8
Offset 12
Rev.1.21