Xilinx 1000BASE-X - Manual (Page 113)

Ethernet 1000BASE-X PCS/PMA or SGMII v9.1 www.xilinx.com 113
UG155 March 24, 2008
Clock Sharing - Multiple Cores with RocketIO, Fabric Elastic Buffer R
Virtex-5 FXT Devices
Figure 8-9 illustrates sharing clock resources across multiple instantiations of the core
when using the Virtex-5 RocketIO GTX 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 GTX 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 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.
Each GTX 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 GTX transceivers.