R

Chapter 5: Using the Client-side GMII Data Path

be included in the frame supplied to the core. The RocketIO transceiver will replace these four bytes with the calculated CRC value.

gmii_txd[7:0]preamble

gmii_tx_en

gmii_tx_er

SFD

4 place holder bytes

Figure 5-8:GMII Frame Transmission with RocketIO Transceiver CRC Logic

Enabled

GMII Reception

The timing of normal inbound frame transfer with RocketIO transceiver CRC functionality is illustrated in Figure 5-9. The RocketIO transceiver calculates the CRC value of the received frame and checks it against that contained in the frames FCS field. The RocketIO transceiver will assert RXCHECKINGCRC and RXCRCERR signals, as defined in the Virtex-II Pro RocketIO Transceiver User Guide. Figure 5-9illustrates a frame received with a correct FCS field since RXCRCERR is not asserted.

Please note that RXCHECKINGCRC and RXCRCERR are obtained directly from the output of the RocketIO transceiver. The core receiver behavior is unchanged.

preamble

SFD

FCS

gmii_rxd[7:0]

 

 

 

gmii_rx_dv

 

 

gmii_rx_er

 

 

RXCHECKINGCRC

 

 

RXCRCERR

 

 

3 clock periods

Figure 5-9:GMII Frame Reception with the RocketIO Transceiver CRC Logic

Enabled

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

UG155 March 24, 2008

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Xilinx 1000BASE-X manual Gmii Reception