Texas Instruments TMS320TCI6486 - Manual (Page 36)

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2.5.4.7 End-of-Packet (EOP) Flag
When set, this flag indicates that the descriptor points to the last packet buffer for a given packet. For a
single fragment packet, both the start-of-packet (SOP) and EOP flags are set. Otherwise, the descriptor
pointing to the last packet buffer for the packet sets the EOP flag. This bit is set by the software
application and is not altered by the EMAC.
2.5.4.8 Ownership (OWNER) Flag
When set, this flag indicates that all the descriptors for the given packet (from SOP to EOP) are currently
owned by the EMAC. This flag is set by the software application on the SOP packet descriptor before
adding the descriptor to the transmit descriptor queue. For a single fragment packet, the SOP, EOP, and
OWNER flags are all set. The OWNER flag is cleared by the EMAC once it is finished with all the
descriptors for the given packet. Note that this flag is valid on SOP descriptors only.
2.5.4.9 End-of-Queue (EOQ) Flag
When set, this flag indicates that the descriptor in question was the last descriptor in the transmit queue
for a given transmit channel, and that the transmitter has halted. This flag is initially cleared by the
software application prior to adding the descriptor to the transmit queue. This bit is set by the EMAC when
the EMAC identifies that a descriptor is the last for a given packet (the EOP flag is set), and there are no
more descriptors in the transmit list (next descriptor pointer is NULL).
The software application can use this bit to detect when the EMAC transmitter for the corresponding
channel has halted. This is useful when the application appends additional packet descriptors to a transmit
queue list that is already owned by the EMAC. Note that this flag is valid on EOP descriptors only.
2.5.4.10 Teardown Complete (TDOWNCMPLT) Flag
This flag is used when a transmit queue is being torn down, or aborted, instead of allowing transmission,
such as during 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. The EMAC does not process subsequent descriptors.
2.5.4.11 Pass CRC (PASSCRC) Flag
The software application sets this flag 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 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.
36 C6472/TCI6486 EMAC/MDIO SPRUEF8F – March 2006 – Revised November 2010
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