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Receive and Transmit Description
22 Software Developer’s Manual
Note: See Table 3-5 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.
3.2.3.2 Receive 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 3-3 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 Chapter 9.
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.
Receive
Descriptor Status
Bits
Description