Clock Sharing - Multiple Cores with RocketIO, Fabric Elastic Buffer

R

Clock Sharing - Multiple Cores with RocketIO, Fabric Elastic Buffer

Virtex-II Pro Devices

Figure 8-7illustrates sharing clock resources across multiple instantiations of the core on the same half of the device when using the core with the RocketIO MGT. Figure 8-7illustrates only two cores; however, more can be added by instantiating the cores using the block level (from the example design) and sharing userclk, userclk2, and brefclk across all instantiations. For each core, userclk and userclk2 must always be derived from the brefclk or refclk used by that core.

Each MGT instantiated has its own independent clock domain synchronous to RXRECCLK which is placed on local clock routing. Each local clock domain must have area constraints added to place it in the region of the MGT. See “Virtex-II Pro RocketIO MGTs for SGMII or Dynamic Standards Switching Constraints,” page 163.

When using the fixed routing resources of brefclk, MGTs along the top edge of the device must use a separate brefclk routing resource to those along the bottom edge of

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

www.xilinx.com

107

UG155 March 24, 2008

Page 107
Image 107
Xilinx manual Ethernet 1000BASE-X PCS/PMA or Sgmii 107