Xilinx 1000BASE-X - Manual (Page 58)

58 www.xilinx.com Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
Chapter 5: Using the Client-side GMII Data Path R
be included in the frame supplied to the core. The RocketIO transceiver will replace these
four bytes with the calculated CRC value.
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 5-9 illustrates 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.
Figure 5-8: GMII Frame Transmission with RocketIO Transceiver CRC Logic
Enabled
gmii_txd[7:0]
gmii_tx_en
gmii_tx_er
preamble
4 place holder bytes
SFD
Figure 5-9: GMII Frame Reception with the RocketIO Transceiver CRC Logic
Enabled
gmii_rxd[7:0]
gmii_rx_dv
gmii_rx_er
preamble FCS
SFD
RXCHECKINGCRC
RXCRCERR
3 clock periods