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Enhanced Three-Speed Ethernet Controllers
15.6.2.5
Ethernet Preamble Customization
By default eTSEC generates a standard Ethernet preamble sequence prior to transmitting frames.
However, the user can substitute a custom preamble sequence for the purpose of controlling switching
equipment at the receiver, particularly at 100/1000Mbps speeds.; in any RMII mode only the standard
preamble can be transmitted.
eTSEC normally searches for and discards the standard Ethernet preamble sequence upon receiving
frames. Part of the received preamble sequence can be optionally recovered and returned as part of the
frame data, making it visible to user software. Note however, that preamble cannot be recovered in any
RMII mode. Note that it is also possible for the first two bytes of custom preamble (PreOct0 and PreOct1)
to be lost in during conversion to ten-bit code groups in the PCS sub-layer. Thus is it recommended that
any custom preamble start at PreOct2.
15.6.2.5.1
User-Defined Preamble Transmission
To substitute a custom preamble, the user must ensure that:
•
MACCFG2[PreAm TxEN] bit is set
•
The first TxBD of every frame containing a custom preamble has its PRE bit set
•
An 8-byte custom preamble sequence appears before the Ethernet DA field in the first transmit data
buffer
The definition of the 8-byte custom preamble sequence is shown in
Byte Offsets
0
1
0–1
2–3
4–5
6–7
The fields of the custom preamble sequence are described in
preamble octets matching the standard start of frame delimiter (0xD5) can be expected to trigger premature
frame reception by the receiving station.
Bytes
Bits
Name
0–1
0–7
PreOct0 Octet #0 of custom transmit preamble. This is the first octet of preamble sent.
8–15
PreOct1 Octet #1 of custom transmit preamble. This is the second octet of preamble sent.
2–3
0–7
PreOct2 Octet #2 of custom transmit preamble. This is the third octet of preamble sent.
8–15
PreOct3 Octet #3 of custom transmit preamble. This is the fourth octet of preamble sent.
4–5
0–7
PreOct4 Octet #4 of custom transmit preamble. This is the fifth octet of preamble sent.
8–15
PreOct5 Octet #5 of custom transmit preamble. This is the sixth octet of preamble sent.
MPC8313E PowerQUICC II Pro Integrated Processor Family Reference Manual, Rev. 3
15-148
2
3
4
5
PreOct0
PreOct2
PreOct4
PreOct6
Figure 15-134. Definition of Custom Preamble Sequence
Table 15-142. Custom Preamble Field Descriptions
Figure
6
7
8
9
10
Table
15-142. It should be noted that use of
Description
15-134.
11
12
13
14
PreOct1
PreOct3
PreOct5
Freescale Semiconductor
15
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