B10B Encoding; Preamble Shortening; Tbi Receive Process; Auto-Negotiation For 1000Base-X - Freescale Semiconductor MPC8313E Family Reference Manual

position of the End_of_Packet symbols (being in either an odd or even position) the eTSEC outputs one
or two Carrier_Extend symbols. Following the last Carrier_Extend symbol, the eTSEC resumes sending
idle codes. If, during a packet, the eTSEC wishes to mark a byte invalid, TX_ER is asserted. The eTSEC,
upon detection of TX_ER, substitutes the data symbol for an Error_Propagation symbol.
15.5.4.1.2

8B10B Encoding

Every eight-bit data octet has two (not necessarily different) ten-bit symbols associated with it. Depending
on the running disparity (the cumulative difference of ones and zeros) the eTSEC module chooses the
appropriate symbol.
Special encapsulation symbols are called ordered_sets. Ordered_sets are comprised of one to four ten-bit
symbols. Ordered_sets can be found in Clause 36 of the IEEE 802.3z specification.
15.5.4.1.3

Preamble Shortening

Because the idle ordered_set comprises two symbols and begins on an even symbols boundary, packets
can only begin on an even boundary. However, the GMII has no such restriction and may signal TX_EN
on an odd boundary. If this happens, the eTSEC delays the Start_of_Packet symbol, effectively ignoring
the first byte of preamble; thus, a seven octet preamble becomes six octets on the Ten-Bit Interface.
15.5.4.2

TBI Receive Process

The eTSEC's TBI Implements the receive portion of the physical coding sublayer as found in Clause 36
of IEEE 802.3z. The Receive portion includes the Synchronization state machine. In SerDes mode, the
eTSEC first attempts to acquire synchronization on the link by examining received symbols. Once
synchronization is acquired, received packets are decoded and sent across the Receive GMII interface. In
GMII mode, the GMII signals are passed through to the MAC.
15.5.4.2.1 Synchronization
The eTSEC examines received symbols looking for the seven bit 'comma' string embedded in some
special symbols. Both the idle ordered_set and the Configuration ordered_set contain a symbol which has
the comma. Once a certain number of codes with comma are detected, the eTSEC is considered to have
acquired synchronization.
15.5.4.2.2

Auto-Negotiation for 1000BASE-X

Once synchronization is acquired, ordered_sets are decoded. If Configuration ordered_sets are received,
the eTSEC decodes the two octet data field and the sixteen-bit Configuration data is stored and used to
Auto-Negotiate with the link partner. in the Receive Configuration Register (RXCR[15:0]) an internal
register used to receive all the link partners informations and used to compare to local ability during
negotiation. Not visible to user. If, during Auto-Negotiation an invalid symbol is detected,
Auto-Negotiation re-starts. After Auto-Negotiation is completed the TBI MII Status Register SR[AN
done] in set. In this mode, packets may be received from the link partner.
MPC8313E PowerQUICC II Pro Integrated Processor Family Reference Manual, Rev. 3
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Enhanced Three-Speed Ethernet Controllers
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