Receive and Transmit Description

Receive

 

Descriptor Status

Description

Bits

 

 

 

 

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.

TCPCS (bit 5)

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.

 

 

 

 

Packet is 802.1Q (matched VET)

 

Indicates whether the incoming packet’s type matches VET (i.e., if the packet is

VP (bit 3)

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 Chapter 9.

 

Reads as 0b.

 

 

 

Ignore Checksum Indication

 

When IXSM = 1b, the checksum indication results (IPCS, TCPCS bits) should be

 

ignored.

IXSM (bit 2)

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.

 

 

Note: See Table 3-5for 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.

3.2.3.2Receive Descriptor Errors Field

Most error information appears only when the Store Bad Packets bit (RCTL.SBP) is set and a bad packet is received. Refer to Table 3-3for 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)

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Software Developer’s Manual

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Intel PCI-X, Intel Gigabit Ethernet Controllers manual Receive Descriptor Errors Field