Data Sheet
Ethernet Controller I210 —Inline Functions
266
Length Field (16)
Length covers the data written to a receive buffer including CRC bytes (if any). Software must read
multiple descriptors to determine the complete length for a packet that spans multiple receive buffers.
Fragment Checksum (16)
This field is used to provide the fragment checksum value. This field equals to the unadjusted 16-bit
ones complement of the packet. Checksum calculation starts at the L4 layer (after the IP header) until
the end of the packet excluding the CRC bytes. In order to use the fragment checksum assist to offload
L4 checksum verification, software might need to back out some of the bytes in the packet. For more
details see Section 7.1.7.2
Status Field (8)
Status information indicates whether the descriptor has been used and whether the referenced buffer is
the last one for the packet. See Table 7-4 for the layout of the Status field. Error status information is
shown in Figure 7-8.
• PIF (bit 7) - Passed imperfect filter only
• IPCS (bit 6) - IPv4 checksum calculated on packet
• L4CS (bit 5) - L4 (UDP or TCP) checksum calculated on packet
• UDPCS (bit 4) - UDP checksum or IP payload checksum calculated on packet.
• VP (bit 3) - Packet is 802.1Q (matched VET); indicates strip VLAN in 802.1Q packet
• RSV (bit 2) - Reserved
• EOP (bit 1) - End of packet
• DD (bit 0) - Descriptor done
EOP and DD
Table 7-5 lists the meaning of these bits:
Table 7-4. Receive Status (RDESC.STATUS) Layout
7 6 5 4 3 2 1 0
PIF IPCS L4CS UDPCS VP Rsv EOP DD
Table 7-5. Receive Status Bits
DD EOP Description
0b 0b Software setting of the descriptor when it hands it off to the hardware.
0b 1b Reserved (invalid option).
1b 0b
A completion status indication for a non-last descriptor of a packet that spans across multiple descriptors. In
a single packet case, DD indicates that the hardware is done with the descriptor and its buffers. Only the
Length fields are valid on this descriptor.
1b 1b
A completion status indication of the entire packet. Note that software Might take ownership of its
descriptors. All fields in the descriptor are valid (reported by the hardware).