Texas Instruments TMS320C674X - Manual (Page 24)

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2.5.4.7 End of Packet (EOP) Flag
When set, this flag indicates that the descriptor points to a packet buffer that is last for a given packet. In
the case of 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 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.
2.5.4.11 Pass CRC (PASSCRC) Flag
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.
24 EMAC/MDIO Module SPRUFL5B – April 2011
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