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AR# 34190

Virtex-6 GTX Aurora 64b/66b - MAP errors out due to incorrect MMCM attributes


The Aurora 64B66B Core uses 400 MHz as the lowest frequency limit for the MMCM's VCO.

This limit is increased to 600 MHz based on characterization data for all Virtex-6 and Virtex-6 -1L devices.

MAP errors out for cores that do not meet the VCO frequency range.

Apart from this issue, MAP generates an error when using the values 1, 2, 3, or 4 or fractional values for CLKFBOUT_MULT_F in MMCM_ADV.


Use the Clocking Wizard v1.4 core's output to update the CLOCK_MODULE for the above mentioned issues.

The Clocking Wizard can be found under 'FPGA Features and Design'/'Clocking' taxonomy in the CORE Generator software.

The Aurora 64B66B Core instantiates two MMCM components, one in CLOCK_MODULE and another in GTX_WRAPPER.

  • The MMCM inside the CLOCK_MODULE is present inside <generated core component name>\example_design\clock_module.
  • The MMCM inside the GTX_WRAPPER is present inside <generated core component name>\example_design\gtx\<generated core component name>_wrapper.

The following table shows the Aurora 64B66B Core's clock_module and  gtx_wrapper parameters with respect to MMCM attributes:

Clocking Wizard's MMCM

Aurora 64B66B Core's MMCM
















To generate the MMCM component, the Clocking Wizard requires the input frequency, (iCLKIN1_FREQ) and the output frequency. 

Use the next procedure to calculate the required input and output frequency values.

1. Input frequency calculation.

  • Input frequency is calculated as (Line rate/16)*1000
  • Line Rate is an Aurora 64B66B core parameter and refers to the c_line_rate parameter in the XCO file.
  • Enter this value as the primary input clock frequency in the Clocking Wizard GUI on page 1.
2. Output frequency1 calculation.
  • Output frequency1 =  ((Line rate/16)*1000) (in MHz)
  • Enter this value as CLK_OUT1 in the Clocking Wizard GUI on page 2.
3. Output frequency2 calculation.
  • Output frequency2 =  ((Line rate/16)*1000)/2 (in MHz)
  • Output frequency2 is the same as the primary input clock frequency calculated in Step 1.
  • Enter this value as CLK_OUT2 in the Clocking Wizard GUI on page 2.
  • Make sure to select the CLK_OUT2 checkbox.
4. Output frequency3 calculation.
  • Output frequency3 =  ((Line rate/16)*1000)/4 (in MHz)
  • Output frequency3 is the same as the primary input clock frequency calculated in Step 1.
  • Enter this value as CLK_OUT3 in the Clocking Wizard GUI on page 2.
  • Make sure to select the CLK_OUT3 check box.
The Clocking wizard displays all of the MMCM attribute values on page 4 of the GUI after the above mentioned steps are followed.

Use the values displayed on page 4 of the GUI to update the Aurora 64B66B Core's CLOCK_MODULE and GTX_WRAPPER, or use the Clocking Wizard Core generated template values to update CLOCK_MODULE and GTX_WRAPPER.

MMCM uses the following simplified formula to calculate VCO frequency range:


Use the above formula and Virtex-6 FPGA Clocking Resources User Guide (UG362) as additional references.


AR# 34190
Date Created 03/03/2010
Last Updated 03/10/2015
Status Active
Type General Article
  • Virtex-6 CXT
  • Virtex-6 LXT
  • Virtex-6 SXT
  • ISE Design Suite - 11.3
  • ISE Design Suite - 11.4
  • ISE Design Suite - 11.5
  • ISE Design Suite - 12.1
  • Aurora
  • Aurora 64B/66B