LAN9211_0711 SMSC [SMSC Corporation], LAN9211_0711 Datasheet - Page 29

• Manufacturer Part Number: LAN9211_0711
• Description: High-Performance Small Form Factor Single-Chip Ethernet Controller with HP Auto-MDIX
• Manufacturer: SMSC [SMSC Corporation]

High-Performance Small Form Factor Single-Chip Ethernet Controller with HP Auto-MDIX
Datasheet
SMSC
3.6.1
LAN9211
Receive Checksum Offload Engine (RXCOE)
The receive checksum offload engine provides assistance to the CPU by calculating a 16-bit checksum
for a received Ethernet frame. The RXCOE readily supports the following IEEE802.3 frame formats:
The resulting checksum value can also be modified by software to support other frame formats.
The RXCOE has two modes of operation. In mode 0, the RXCOE calculates the checksum between
the first 14 bytes of the Ethernet frame and the FCS. This is illustrated in
In mode 1, the RXCOE supports VLAN tags and a SNAP header. In this mode the RXCOE calculates
the checksum at the start of L3 packet. The VLAN1 tag register is used by the RXCOE to indicate
what protocol type is to be used to indicate the existence of a VLAN tag. This value is typically 8100h.
Example frame configurations:
1DWORD
DST
0
Type II Ethernet frames
SNAP encapsulated frames
Support for up to 2, 802.1q VLAN tags
DST
1
SRC
2
SRC
p
r
o
t
3
T
Y
P
E
Figure 3.3 RXCOE Checksum Calculation
Figure 3.4 Type II Ethernet Frame
DATASHEET
Calculate Checksum
Calculate Checksum
29
Frame Data
L3 Packet
Figure
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Revision 1.93 (11-27-07)
3.3.
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