Intel PCI User Manual

22

Note: See 

 for a description of supported packet types for receive checksum offloading. 

Unsupported packet types either have the IXSM bit set, or they don’t have the TCPCS bit set.

Most error information appears only when the Store Bad Packets bit (RCTL.SBP) is set and a bad 

packet is received. Refer to 

 for a definition of the possible errors and their bit positions.

The error bits are valid only when the EOP and DD bits are set in the descriptor status field 

(RDESC.STATUS)

TCPCS (bit 5)

TCP Checksum Calculated on Packet
When Ignore Checksum Indication is deasserted (IXSM = 0b), TCPCS bit 
indicates whether the hardware performed the TCP/UDP checksum on the 
received packet. 
0b = Do not perform TCP/UDP checksum; 1b = Perform TCP/UDP checksum
Pass/Fail information regarding the checksum is indicated in the error bit (TCPE) 
of the descriptor receive errors (RDESC.ERRORS).
IPv6 packets may have this bit set if the TCP/UDP packet was recognized.
Reads as 0b.

RSV (bit 4)

Reserved
Reads as 0b.

VP (bit 3)

Packet is 802.1Q (matched VET)
Indicates whether the incoming packet’s type matches VET (i.e., if the packet is 
a VLAN (802.1q) type). It is set if the packet type matches VET and CTRL.VME 
is set. For a further description of 802.1q VLANs, see 

.

Reads as 0b.

IXSM (bit 2)

Ignore Checksum Indication
When IXSM = 1b, the checksum indication results (IPCS, TCPCS bits) should be 
ignored.
When IXSM = 0b the IPCS and TCPCS bits indicate whether the hardware 
performed the IP or TCP/UDP checksum(s) on the received packet. Pass/Fail 
information regarding the checksum is indicated in the status bits as described 
below for IPE and TCPE.
Reads as 1b.

EOP (bit 1)

End of Packet
EOP indicates whether this is the last descriptor for an incoming packet.

DD (bit 0)

Descriptor Done
Indicates whether hardware is done with the descriptor. When set along with 
EOP, the received packet is complete in main memory.