LAN9211 datasheet(29/146 Pages) SMSC

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High-Performance Small Form Factor Single-Chip Ethernet Controller with HP Auto-MDIX

Datasheet

SMSC

LAN9211

Revision 1.93 (11-27-07)

DATASHEET

3.6.1

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:

Type II Ethernet frames

SNAP encapsulated frames

Support for up to 2, 802.1q VLAN tags

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 Figure 3.3.

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:

Figure 3.3 RXCOE Checksum Calculation

Figure 3.4 Type II Ethernet Frame

DST

SRC

Frame Data

Calculate Checksum

DST

SRC

L3 Packet

Calculate Checksum

1DWORD

LAN9211 Datasheet(PDF) 29 Page - SMSC Corporation