Start of Frame Encoding

R

Reception of the Even Case

Figure D-2illustrates the reception of the in-bound code-group stream, received either serially using the RocketIO transceiver, or in parallel across the TBI, and translation of this code-group stream into the receiver GMII. This is performed by the PCS Receive Engine.

The Start of Packet code group /S/ is replaced with a preamble byte. This results in the restoration of the full preamble field.

rx_code_group I2 I2 I2 S preamble

SFD

PCS Receive Engine Decoding

gmii_rxd[7:0]

preamble

gmii_rx_dv

gmii_rx_er

SFD

Figure D-2:1000BASE-X Reception State Machine Operation (Even Case)

The Odd Transmission Case

Figure D-3illustrates the translation of GMII encoding into the code-group stream performed by the PCS Transmit Engine; this stream is transmitted out of the core, either serially using the RocketIO transceiver, or in parallel across the TBI.

In this example, the assertion of the gmii_tx_en signal of the GMII occurs in the odd position; in response, the state machines are unable to immediately insert a Start-Of-Packet code group /S/ as the Idle character must first be completed. The Start of Packet code group /S/ is therefore inserted (in the even position) after completing the Idle. This results in the /D16.2/ character of the Idle /I2/ sequence being inserted in place of the first byte of the preamble field, and the Start-Of-Packet /S/ being inserted in place of the second byte of preamble as illustrated.

Ethernet 1000BASE-X PCS/PMA or SGMII v9.1

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UG155 March 24, 2008

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Xilinx 1000BASE-X manual Reception of the Even Case, Odd Transmission Case, Start of Frame Encoding