Data Sheet

Ethernet Controller I210 —Inline Functions
296
RS signals hardware to report the status information. This is used by software that does in-memory
checks of the transmit descriptors to determine which ones are done. For example, if software queues
up 10 packets to transmit, it can set the RS bit in the last descriptor of the last packet. If software
maintains a list of descriptors with the RS bit set, it can look at them to determine if all packets up to
(and including) the one with the RS bit set have been buffered in the output FIFO. Looking at the status
byte and checking the DD bit do this. If DD is set, the descriptor has been processed. Refer to the next
section for the layout of the status field.
Note: Descriptors with zero length transfer no data.
IFCS, when set, hardware appends the MAC FCS at the end of the packet. When cleared, software
should calculate the FCS for proper CRC check. There are several cases in which the hardware changes
the packet, and thus the software must set IFCS:
• Transmitting a short packet while padding is enabled by the TCTL.PSP bit.
• Checksum offload is enabled by the either the TXSM or IXSM bits in the TDESD.POPTS field.
• VLAN header insertion enabled by the VLE bit in the TDESD.DCMD descriptor field when the
VMVIR[n].VLANA register field is 0.
• TCP/UDP segmentation offload enabled by TSE bit in the TDESD.DCMD.
EOP indicates whether this is the last buffer for an incoming packet.
7.2.2.3.6 STA (4)
• Rsv (bits 2-3) - Reserved
• TS_STAT (bit 1) - DMA Timestamp is provided in the DMA Time Stamp field. It is enabled by the
1588_STAT_EN flag in the TQAVCTRL register.
• DD (bit 0) - Descriptor Done
7.2.2.3.7 IDX (3)
Index into the hardware context table to indicate which context should be used for this request. If no
offload is required, this field is not relevant and no context needs to be initiated before the packet is
sent. See Table 7-32 for details on type of transmit packet offloads that require a context reference.
7.2.2.3.8 POPTS (6)
• Reserved (bits 5:2)
• TXSM (bit 1) - Insert L4 Checksum
• IXSM (bit 0) - Insert IP Checksum
TXSM, when set to 1b, L4 checksum must be inserted. In this case, TUCMD.L4T in the context
descriptor indicates whether the checksum is TCP, UDP, or SCTP.
Table 7-37. Transmit Data (TDESD.POPTS) Layout
521 0
Reserved TXSM IXSM