Functional Description
0 - The Tx queue has more packets to transfer.
1 - The Descriptor buffer is the last buffer in the last packet in the queue.
teardown_Complete
This flag is used when a transmit queue is being torn down, or aborted, instead of allowing it to be
transmitted. This would happen under device driver reset or shutdown conditions. The EMAC sets this bit
in the SOP descriptor of each packet as it is aborted from transmission. Note that this flag is valid on SOP
descriptors only. Also note that only the first packet in an unsent list has the TDOWNCMPLT flag set.
Subsequent descriptors are not processed by the EMAC.
0 - The port has not completed the teardown process.
1 - The port has completed the commanded teardown process.
pass_crc
This flag is set by the software application in the SOP packet descriptor before it adds the descriptor to the
transmit queue. Setting this bit indicates to the EMAC that the 4 byte Ethernet CRC is already present in
the packet data, and that the EMAC should not generate its own version of the CRC.When the CRC flag is
cleared, the EMAC generates and appends the 4-byte CRC. The buffer length and packet length fields do
not include the CRC bytes. When the CRC flag is set, the 4-byte CRC is supplied by the software
application and is already appended to the end of the packet data. The buffer length and packet length
fields include the CRC bytes, as they are part of the valid packet data. Note that this flag is valid on SOP
descriptors only.
0 – The CRC is not included with the packet data and packet length.
1 – The CRC is included with the packet data and packet length.
to_port
To Port – Port number to send the directed packet to. This field is set by the host. This field is valid on
SOP. Directed packets go to the directed port, but an ALE lookup is performed to determine untagged
egress in VLAN_AWARE mode.
1 – Send the packet to port 1 if to_port_en is asserted.
2 – Send the packet to port 2 if to_port_en is asserted.
To_port_enable
To Port Enable – Indicates when set that the packet is a directed packet to be sent to the to_port field port
number. This field is set by the host. The packet is sent to one port only (index not mask). This bit is valid
on SOP.
0 – not a directed packet
1 – directed packet
Packet Length
Specifies the number of bytes in the entire packet. Offset bytes are not included. The sum of the
buffer_length fields should equal the packet_length. Valid only on SOP. The packet length must be greater
than zero. The packet data will be truncated to the packet length if the packet length is shorter than the
sum of the packet buffer descriptor buffer lengths. A host error occurs if the packet length is greater than
the sum of the packet buffer descriptor buffer lengths
14.3.2.4.1.2 RX Buffer Descriptors
An RX buffer descriptor is a contiguous block of four 32-bit data words aligned on a 32-bit word boundary.
1189
SPRUH73H – October 2011 – Revised April 2013
Ethernet Subsystem
Copyright © 2011–2013, Texas Instruments Incorporated