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AR# 23362

Virtex-4 XAUI Core - Core needs a 2x Reference Clock to avoid high jitter from MGT


The Virtex-4 FX Errata specifies that GT11 transceivers with reference clocks at 156.25 MHz will have high jitter on the serial line. For more information on this issue, please consult the Virtex-4 FX Errata.


Versions 6.2 of the XAUI Core and later have been updated to use a 312.5MHz clock. If a different reference clock has to be used, the Rocket IO Wizard can be run to generate the correct attributes to change the reference clock frequency. For XAUI v7.0 and later, the rocketio_wrapper.v/vhd can be directly replaced with the rocketio_wrapper.v/vhd generated from the RocketIO Wizard.

Use the following steps to replace the original rocketio_wrapper.v/vhd in the XAUI core example_design directory:

1. Run the RocketIO Wizard in CORE Generator with the correct target device. Leave all of the options as the default, except:

-On page 1, of the RocketIO Wizard, select the following:

The component name must be rocketio_wrapper, which is the default.

protocol file: xaui

silicon version: select the silicon version being used

- On page 2, choose the GT11s that will be used.

- On page 3, set the reference clock rate

2. The output will contain the constraints embedded into the GT11 wrapper code in <coregen_project>/<core_name>/src/rocketio_wrapper.v/vhd. Copy this file into the XAUI core example_design directory.

AR# 23362
Date 12/15/2012
Status Active
Type General Article
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