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AR# 34144

Virtex-6 Integrated Block Wrapper v1.4 for PCI Express - Incorrect MMCM VCO settings result in "ERROR:PhysDesignRules:1995 - The computed value for the VCO operating frequency..."


The MMCM attribute settings in the v1.4 core are incorrect. Users should download the filesprovided in this Answer Record to obtain the correct settings. Implementation with ISE 11.4 design toolsdoes not indicate any error message, but the settings should be updated.

After updating your ISE software to any version greater than 11.4, the following error occurs:

"ERROR:PhysDesignRules:1995 - The computed value for the VCO operating frequency of MMCM_ADV instance cgator_wrapper/rport/pcie_clocking_i/mmcm_adv_i is calculated to be 500.000000 MHz. This falls below the operatingrange of the MMCM VCO frequency for this device of 600.000000 - 1200.000000 MHz. Please adjust either the inputfrequency CLKINx_PERIOD, multiplication factor CLKFBOUT_MULT_F or the division factor DIVCLK_DIVIDE, in order to achieve a VCO frequency within the rated operating range for this device."

This error occurs because of changes in the MMCM requirements, and previous settings used by the core no longer work in software versions greater than 11.4.


An update is available in(Xilinx Answer 34279); download the ZIP file titled "ar34279_v6_pcie_v1_4.zip" from the Answer Record.

The ZIP file contains a file titled pcie_clocking_v6.v[hd] which contains new settings for the MMCM VCO parameters. Place this file in your generated core's source directory.

Note that this ZIP file is cumulative and can contain fixes for other problems as described in (Xilinx Answer 34279).

Revision History:
03/04/2010 - Updated to refer to 34279
01/27/2010 - Initial Release

Linked Answer Records

Master Answer Records

Associated Answer Records

AR# 34144
Date 05/22/2012
Status Active
Type Known Issues
  • Virtex-6 LXT
  • Virtex-6 FPGA Integrated Block for PCI Express ( PCIe )