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Chapter 7: 1000BASE-X with RocketIO Transceivers
Virtex-5 FXT Devices
Figure 7-8 illustrates sharing clock resources across multiple instantiations of the core when using Virtex-5 RocketIO GTX transceivers.
The example design can be generated to connect either a single instance of the core or connect a pair of core instances to the transceiver pair present in a GTX tile. Figure 7-8 illustrates two instantiations of the block level, and each block level contains a pair of cores, consequently illustrating clock sharing between a total of four cores.
Additional cores can be added by continuing to instantiate extra block level modules. Share the brefclk_p and brefclk_n differential clock pair. See the Virtex-5 RocketIO GTX Transceiver User Guide for more information.
To provide the FPGA fabric clocks for all core instances, select a REFCLKOUT port from any GTX transceiver and route this to a single DCM. The CLK0 (125MHz) and CLKDV (62.5MHz) outputs from this DCM, placed onto global clock routing using a BUFGs, can be shared across all core instances and GTX transceivers as illustrated.
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| UG155 March 24, 2008 |