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326 Software Developer’s Manual
Register Descriptions
Field Bit(s)
Initial
Value
Description
PCSS 7:0 0b
Packet Checksum Start
Controls the starting byte for the Packet Checksum
calculation. The Packet Checksum is the one’s complement
over the receive packet, starting from the byte indicated by
RXCSUM.PCSS (0b corresponds to the first byte of the
packet), after stripping. For example, for an Ethernet II frame
encapsulated as an 802.3ac VLAN
1
packet and with
RXCSUM.PCSS set to 14, the packet checksum would
include the entire encapsulated frame, excluding the 14-byte
Ethernet header (DA,SA,Type/Length) and the 4-byte VLAN
tag. The Packet Checksum does not include the Ethernet
CRC if the RCTL.SECRC bit is set. Software must make the
required offsetting computation (to back out the bytes that
should not have been included and to include the pseudo-
header) prior to comparing the Packet Checksum against the
TCP checksum stored in the packet.
IPOFLD 8 0b
IP Checksum Off-load Enable
RXCSUM.IPOFLD is used to enable the IP Checksum
offloading feature. If RXCSUM.IPOFLD is set to 1b, the
Ethernet controller calculates the IP checksum and indicates
a pass/fail indication to software through the Checksum Error
bit (CSE) in the ERROR field to the receive descriptor. If both
RXCSUM.IPOFLD and RXCSUM.TUOFLD are set, the
Checksum Error bit (CSE) is set if either checksum was
incorrect. If neither RSCSUM.IPOFLD nor
RXCSUM.TUOFLD is set, the Checksum Error bit (CSE) is
be 0b for all packets.
TUOFLD 9 0b
TCP/UDP Checksum Off-load Enable
RXCSUM.TUOFL is used to enable the TCP/UDP Checksum
off-loading feature. When set to 1b, the Ethernet controller
calculates the TCP or UDP checksum and indicate a pass/fail
indication to software through the Checksum Error bit (CSE).
If both RXCSUM.TUOFLD and RXCSUM.TUOFLD are set,
the Checksum Error bit (CSE) is set if either checksum was
incorrect. If neither RXCSUM.IPOFLD nor
RXCSUM.TUOFLD is set, the Checksum Error bit (CSE) is
0b for all packets.
IPV6OFL
2
10 0b
IPv6 Checksum Offload Enable
If IPV6OFL is set to 1b, hardware parses IPv6 headers when
parsing a receive packet. This applies to checksum offloading
only.
Reserved 31:11 0b
Reserved
Reads as 0b. Should be written with 0b for future
compatibility.
1. Not applicable to the 82541ER.
2. Not applicable to the 82544GC/EI.