
Clock Sharing - Multiple Cores with RocketIO, Fabric Elastic Buffer
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Virtex-5 LXT and SXT Devices
Figure 8-9 illustrates sharing clock resources across multiple instantiations of the core when using the Virtex-5 RocketIO GTP transceiver. 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 GTP transceiver tile. Figure 8-9 illustrates two instantiations of the block level, and each block level contains a pair of cores. Figure 8-9 illustrates clock sharing between four cores.
More cores can be added by instantiating extra block level modules. Share the brefclk_p and brefclk_n differential clock pairs. See the Virtex-5 RocketIO GTP Transceiver User Guide for more information.
To provide the 125 MHz clock for all core instances, select a REFCLKOUT port from any GTP transceiver. This can be routed onto global clock routing using a BUFG as illustrated and shared between all cores and GTP transceivers in the column.
Each GTP and core pair instantiated has its own independent clock domains synchronous to RXRECCLK0 and RXRECCLK1. These are placed on regional clock routing using a BUFR, as illustrated in Figure 8-9, and cannot be shared across multiple GTP transceivers.
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