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Chapter 9: Constraining the Core

The RGMII v2.0 is a 1.5 volt signal-level interface. The 1.5 volt HSTL Class I SelectIO standard is used for RGMII interface pins. Use the following constraints with the device IO Banking rules. The IO slew rate is set to fast to ensure that the interface can meet setup and hold times.

INST "rgmii_txd<?>"

IOSTANDARD = HSTL_I;

INST "rgmii_tx_ctl"

IOSTANDARD = HSTL_I;

INST "rgmii_rxd<?>"

IOSTANDARD = HSTL_I;

INST "rgmii_rx_ctl"

IOSTANDARD = HSTL_I;

INST "rgmii_txc"

IOSTANDARD = HSTL_I;

INST "rgmii_rxc"

IOSTANDARD = HSTL_I;

INST "rgmii_txd<?>"

SLEW = FAST;

INST "rgmii_tx_ctl"

SLEW = FAST;

INST "rgmii_txc"

SLEW = FAST;

In addition, the example design provides pad locking on the RGMII for several families. This is provided as a guideline only; there are no specific I/O location constraints for this core.

RGMII Input Setup/Hold Timing

Figure 9-3and Table 9-2illustrate the setup and hold time window for the input RGMII signals. This is the worst-case data valid window presented to the FPGA device pins.

RGMII_RXC

RGMII_RXD[3:0],

RGMII_RX_CTL

tSETUP

tHOLD

Figure 9-3:Input RGMII Timing

tSETUP tHOLD

The 2 ns data valid window, which is presented across the RGMII input bus, must be correctly sampled on both clock edges by the FPGA devices.

Table 9-2:Input RGMII Timing

Symbol

Min

Typical

Units

 

 

 

 

tSETUP

1.0

2.0

ns

tHOLD

1.0

2.0

ns

For RGMII, the lower data bits, rgmii_rxd[3:0], should be sampled internally on the rising edge of rgmii_rxc, and the upper data bits, rgmii_rxd[7:4], should be sampled internally on the falling edge of rgmii_rxc.

The following constraints are provided in the UCF for RGMII Example Designs. These constraints invoke the tools to analyze the setup/hold requirements (though, if failing, the tools are NOT capable of fixing them: meeting these constraints is a manual process - see the following family specific sections for details):

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UG144 April 24, 2009

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Xilinx UG144 manual Rgmii Input Setup/Hold Timing, 2Input Rgmii Timing Symbol Min Typical Units

UG144 specifications

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