R

Chapter 5: Using the Client-side GMII Data Path

10 Megabit per Second Frame Transmission

The operation of the core remains unchanged. It is the responsibility of the client logic (for example, an Ethernet MAC), to enter data at the correct rate. When operating at a speed of 10 Mbps, every byte of the MAC frame (from destination address to the frame check sequence field, inclusive) should each be repeated for 100 clock periods to achieve the desired bit rate. It is also the responsibility of the client logic to ensure that the interframe gap period is legal for the current speed of operation.

GMII Reception

1 Gigabit per Second Frame Reception

The timing of normal inbound frame transfer is illustrated in Figure 5-12. At 1 Gbps speed, the operation of the receiver GMII signals remains identical to that described in “Designing with the Client-side GMII for the 1000BASE-X Standard” in Chapter 5.

userclk2

gmii_rxd[7:0]preamble

gmii_rx_dv

gmii_rx_er

SFD D0

D1

FCS

Figure 5-12:GMII Frame Reception at 1 Gbps

100 Megabit per Second Frame Reception

The operation of the core remains unchanged. When operating at a speed of 100 Mbps, every byte of the MAC frame (from destination address to the frame check sequence field, inclusive) is repeated for 10 clock periods to achieve the desired bit rate. See Figure 5-13. It is the responsibility of the client logic, for example an Ethernet MAC, to sample this data correctly.

userclk2

gmii_rxd[7:0]

gmii_rx_dv

gmii_rx_er

preamble

SFD

D0

D1

 

 

10 clock periods

 

Figure 5-13:GMII Data Reception at 100 Mbps

 

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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 Gigabit per Second Frame Reception, Megabit per Second Frame Reception