Transmit Descriptor Format; Figure 9-14. Multiple Fragments Per Transmit Frame - Cirrus Logic EP93 Series User Manual

1/10/100 Mbps Ethernet LAN Controller
EP93xx User's Guide
9
Example: Fragments 0, 1, 2 make-up one complete frame.
register sizes are in bits,
and shown in parentheses ().
EOF = 0
EOF = 0
EOF = 1
In the example shown in
MAC starts the frame by acquiring the medium and transmitting the preamble. Then, the
fragments 0, 1, 2 are transmitted in order for a total of 446 bytes (39 + 388 + 19). Since the
CRC bit in the first frame fragment is clear, the HW appends the 4 byte CRC. Thus, 4 more
bytes are added to the frame for the CRC making the total frame length 450 bytes. Finally, the
MAC sends the end-of-frame.
The CMD field is 4 bits. Only the AF bit is valid. The other fields are reserved.

9.2.3.9 Transmit Descriptor Format

Transmit Descriptor Format - First Word
31 30
15 14
Definition:
9-28
T x B u fA d r 0 ( 3 2 )
Buffer CMD Buffer
EOF
Index 0 (15) (4) Length 0 (12)
T x D B u f A d r 1 ( 3 2 )
Buffer CMD
Buffer
EOF
Index 0 (15) (4)
Length 0 (12)
T x D B u f A d r 2 ( 3 2 )
Buffer Buffer
EOF CMD
Index 0 (15) Length 0 (12)
(4)

Figure 9-14. Multiple Fragments Per Transmit Frame

Figure
29 28 27 26
13 12 11 10
Transmit Descriptor, first word. Contains the base address of the data buffer.
Copyright 2007 Cirrus Logic
9-14, one frame is transmitted from three fragments. The
25 24 23 22
TBA
9 8 7 6
TBA
Data Fragment 0
Fragment 0
Data Fragment 1
Fragment 1
388 bytes
Fragment 2
Data Fragment 2
21 20 19 18
5 4 3 2
Length
89 bytes
Length
Length
19 bytes
17 16
1 0
DS785UM1