Functional Description
The byte aligned memory address of the buffer associated with the buffer descriptor. The host sets the
buffer_pointer. The software application must set this value prior to adding the descriptor to the active
transmit list. This pointer is not altered by the EMAC.
14.3.2.4.1.1.3 CPPI Tx Data Word – 2
Buffer _Offset
Buffer Offset – Indicates how many unused bytes are at the start of the buffer. A value of 0x0000 indicates
that no unused bytes are at the start of the buffer and that valid data begins on the first byte of the buffer.
A value of 0x000F (decimal 15) indicates that the first 15 bytes of the buffer are to be ignored by the port
and that valid buffer data starts on byte 16 of the buffer. The host sets the buffer_offset value (which may
be zero to the buffer length minus 1). Valid only on sop.
Buffer _Length
Buffer Length – Indicates how many valid data bytes are in the buffer. Unused or protocol specific bytes at
the beginning of the buffer are not counted in the Buffer Length field. The host sets the buffer_length. The
buffer_length must be greater than zero.
14.3.2.4.1.1.4 CPPI Tx Data Word – 3
Start of Packet (SOP) Flag
When set, this flag indicates that the descriptor points to a packet buffer that is the start of a new packet.In
the case of a single fragment packet, both the SOP and end of packet (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.
0 - Not start of packet buffer
1 - Start of packet buffer
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.
0 - Not end of packet buffer.
1 - End of packet buffer.
Ownership
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.
0 - The packet is owned by the host
1 - The packet is owned by the port
EOQ
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.
1188
Ethernet Subsystem
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated