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Appendix D: 1000BASE-X State Machines
Reception of the Even Case
Figure D-6 illustrates 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.
rx_code_group | FCS | T R I1/I2 I2 | I2 | I2 |
PCS Receive Engine Decoding
gmii_rxd[7:0] | FCS |
gmii_rx_dv |
|
gmii_rx_er |
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Figure D-6: 1000BASE-X Reception State Machine Operation (Even Case)
The Odd Transmission Case
Figure D-7 illustrates 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 response to the deassertion of gmii_tx_en, an End of Packet code group /T/ is immediately inserted. Note that the even and odd alignment described in “Start of Frame Encoding” persists throughout the Ethernet frame. If the /T/ character occurs in the odd position (the frame contained an odd number of bytes starting from the /S/ character), then this is followed with two Carrier Extend code groups /R/. This allows the /K28.5/ character of the following Idle code group to be aligned to the even position.
216 | www.xilinx.com | Ethernet |
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| UG155 March 24, 2008 |