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AR# 31457

Virtex-5 GTX RocketIO - Spread Spectrum Clocking attribute changes

Description

Keywords: RocketI/O, SSC

The SATA specification allows the use of Spread Spectrum Clocking (SSC) at both Gen1 and Gen2 speeds, 1.5 Gb/s and 3.0 Gb/s respectively. Alternate values for the PMA_RX_CFG attribute should be used to ensure reliable operation while using SSC at these speeds.

Solution

Xilinx recommends the following settings be used when using Spread Spectrum Clocking at SATA line rates:

Gen1 at 1.5 Gb/s with PLL_RXDIVSEL_OUT = 2: PMA_RX_CFG = 0x0E100D5

Gen2 at 3.0 Gb/s with PLL_RXDIVSEL_OUT = 1: PMA_RX_CFG = 0x0E10089

These values differ from those generated by the RocketIO GTX Wizard, and they will need to be modified in the generated wrapper file. The Wizard is scheduled to be updated in a future release to include these values.

For non-SATA applications intending to use similar SSC characteristics, these attributes should still be used. Using the attribute settings associated with the PLL_RXDIVSEL_OUT value are recommended, though have not been tested outside the SATA line rates.
AR# 31457
Date Created 08/14/2008
Last Updated 11/17/2009
Status Active
Type General Article