Intel PCI User Manual

Page of 406
322
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.