RocketIO Transceiver Logic

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Virtex-4 FX Devices

The core is designed to integrate with the Virtex-4 RocketIO MGT. Figure 7-2illustrates the connections and logic required between the core and MGT—the signal names and logic in the figure precisely match those delivered with the example design when an MGT is used.

Note: A small logic shim (included in the block-level wrapper) is required to convert between the port differences between the Virtex-II Pro and Virtex-4 RocketIO transceivers.

The MGT clock distribution in Virtex-4 devices is column-based and consists of multiple MGT tiles (each tile contains two MGTs). For this reason, the MGT wrapper delivered with the core always contains two MGT instantiations, even if only a single MGT is in use.

Figure 7-2illustrates a single MGT tile for clarity.

A GT11CLK_MGT primitive is also instantiated to derive the reference clocks required by the MGT column-based tiles. See the Virtex-4 RocketIO Multi-Gigabit Transceiver User Guide (UG076) for information about layout and clock distribution.

The 250 MHz reference clock from the GT11CLK_MGT primitive is routed to the MGT, configured to internally synthesize a 125 MHz clock. This is output on the TXOUTCLK1 port of the MGT and after placed onto global clock routing, can be used by all core logic. This clock is input back into the MGT on the user interface clock ports rxusrclk2 and txusrclk2. With the attribute settings applied to the MGT from the example design, the txusrclk and rxusrclk ports are derived internally within the MGT using the internal clock dividers and do not need to be provided from the FPGA fabric.

The Virtex-4 FX MGTs require the inclusion of a calibration block in the fabric logic; the example design provided with the core instantiates calibration blocks as required. Calibration blocks require a clock source of between 25 to 50 MHz that is shared with the Dynamic Reconfiguration Port (DRP) of the MGT, which is named dclk in the example design. See Xilinx Answer Record 22477 for more information.

Figure 7-2also illustrates the TX_SIGNAL_DETECT and RX_SIGNAL_DETECT ports of the calibration block, which should be driven to indicate whether or not dynamic data is being transmitted and received through the MGT (see Virtex-4 Errata). However, RX_SIGNAL_DETECT is connected to the signal_detect port of the example design. signal_detect is intended to be connected to the optical transceiver to indicate the presence of light. When light is detected, the optical transceiver provides dynamic data to the Rx ports of the MGT. When no light is detected, the calibration block switches the MGT into loopback to force dynamic data through the MGT receiver path.

Caution! signal_detect is an optional port in the IEEE 802.3 specification. If this is not used, the RX_SIGNAL_DETECT port of the calibration block must be driven by an alternative method. Please refer to XAPP732 for more information.

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

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UG155 March 24, 2008

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Xilinx 1000BASE-X manual Virtex-4 FX Devices, RocketIO Transceiver Logic