Data Sheet

Inline Functions—Ethernet Controller I210
271
reflect the size of the data actually stored in the header buffer because the I210 fills the buffer up to
the size configured by SRRCTL[n].BSIZEHEADER, which might be larger than the header size reported
here. This field is only valid in the first descriptor of a packet and should be ignored in all subsequent
descriptors.
Note: When the packet is time stamped and the time stamp is placed at the beginning of the buffer
the RDESC.HDR_LEN field is updated with the additional time stamp bytes (16 bytes). For
further information see Section 7.1.7.
Packet types supported by the header split and header replication are listed in Appendix A.1. Other
packet types are posted sequentially in the host packet buffer. Each line in Table 7-13 has an enable bit
in the PSRTYPE register. When one of the bits is set, the corresponding packet type is split. If the bit is
not set, a packet matching the header layout is not split.
Header split and replication is described in Section 7.1.5 while the packet types for this functionality are
enabled by the PSRTYPE[n] registers (Section 8.10.3).
Note: The header of a fragmented IPv6 packet is defined before the fragmented extension header.
SPH (1) - Split Header - When set, indicates that the HDR_LEN field reflects the length of the header
found by hardware. If cleared, the HDR_LEN field should be ignored.In the case where
SRRCTL[n].DESCTYPE is set to Header replication mode, SPH bit is set but the HDR_LEN field does not
reflect the size of the data actually stored in the header buffer, because the I210 fills the buffer up to
the size configured by SRRCTL[n].BSIZEHEADER.
RSS Hash / {Fragment Checksum, IP identification} (32)
This field has multiplexed functionality according to the received packet type (reported on the Packet
Type field in this descriptor) and device setting.
Fragment Checksum (16-Bit; 63:48)
The fragment checksum word contains the unadjusted one’s complement checksum of the IP
payload and is used to offload checksum verification for fragmented UDP packets as described in
Section 7.1.7.2. This field is mutually exclusive with the RSS hash. It is enabled when the
RXCSUM.PCSD bit is cleared and the RXCSUM.IPPCSE bit is set.
IP identification (16-Bit; 47:32)
The IP identification word identifies the IP packet to whom this fragment belongs and is used to
offload checksum verification for fragmented UDP packets as described in Section 7.1.7.2. This
field is mutually exclusive with the RSS hash. It is enabled when the RXCSUM.PCSD bit is cleared
and the RXCSUM.IPPCSE bit is set.
RSS Hash Value (32)
The RSS hash value is required for RSS functionality as described in Section 7.1.2.7. This bit is
mutually exclusive with the fragment checksum. It is enabled when the RXCSUM.PCSD bit is set.
Extended Status (20)
Status information indicates whether the descriptor has been used and whether the referenced buffer is
the last one for the packet. Table 7-13 lists the extended status word in the last descriptor of a packet
(EOP is set). Table 7-14 lists the extended status word in any descriptor but the last one of a packet
(EOP is cleared).