Texas Instruments TMS320C645x DSP manual End of Packet EOP Flag, Ownership Owner Flag

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EMAC Functional Architecture

2.5.4.7End 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.

2.5.4.8Ownership (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.

2.5.4.9End 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.

2.5.4.10Teardown 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.

2.5.4.11Pass 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.

32 Ethernet Media Access Controller (EMAC)/Management Data Input/Output (MDIO) SPRU975B –August 2006

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