R

Chapter 5: Using the Client-side GMII Data Path

gmii_tx_clk

IPAD

gmii_txd[0]

IPAD

gmii_tx_en

IPAD

gmii_tx_er

IPAD

Virtex-4 Devices

The logic described previously for Virtex-II and Virtex-II Pro devices does not meet the input setup and hold requirements for GMII with Virtex-4 devices. Two possible solutions are:

1.A DCM may be used on the gmii_tx_clk clock path for the Spartan-3 family, as illustrated in Figure 5-15.

2.Input Delay Elements may be used on the GMII data path, as illustrated in Figure 5-16.

The IODELAY elements can be adjusted to fine-tune the setup and hold times at the GMII IOB input flip-flops. The delay is applied to the IODELAY element using constraints in the UCF; these can be edited if desired. See “Constraints When Implementing an External GMII” in Chapter 12 for more information.

 

 

IOB LOGIC

Ethernet 1000BASE-X

 

 

 

 

 

 

 

 

PCS/PMA

IBUFG

 

 

 

or SGMII LogiCORE

 

 

 

BUFG

 

 

 

 

gmii_tx_clk_bufg

 

 

IDELAY

 

 

 

 

 

 

 

 

 

 

 

 

 

 

userclk2 (if RocketIO is used) gtx_clk (if TBI is used)

Transmitter

Elastic

Buffer

IBUF

IDELAY

D Q

gmii_txd_int[0]

gmii_txd[0]

IBUF

IDELAY

D Q

gmii_tx_en_int

gmii_tx_en

 

IBUF

IDELAY

D Q

gmii_tx_er_int

gmii_tx_er

 

Figure 5-16:External GMII Transmitter Logic for Virtex-4 Devices

64

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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 16External Gmii Transmitter Logic for Virtex-4 Devices