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STP2002QFP
Fast Ethernet, Parallel Port, SCSI (FEPS) - STP2002QFP
Sun Microsystems,
5.2.8 Transmit FIFO Data Structures
When a transmit packet is transferred from the host into the local memory, the
first byte of the packet in the FIFO is always loaded to be word (or double-
word) aligned. If the packet is composed of several data buffers, the data buff-
ers are concatenated as a contiguous byte stream in the FIFO (gather func-
tion). The last byte of a packet can reside at any byte boundary, therefore the
last data word of the packet is marked by a tag. At the end of the packet a con-
trol word is appended, which is again marked by a tag bit. The control word
indicates the last byte boundary for the packet.
5.2.9 Receive FIFO Data Structures
When a receive packet is transferred from the RX_MAC into the local mem-
ory, the half-word (16-bit) data stream is packed into words (or double
words), with the first byte of the packet starting at a programmable offset
within the first word.
Even though the receive data structure’s functionality does not require to
tag the last data word of a packet, the hardware will do that to provide a more
robust implementation.
At the end of the packet a status word is appended, which is again marked
by a tag bit. This word provides status information about the received frame,
which is either passed to the device driver or used for unloading the frame
from the RxFIFO.