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AR# 34189

RocketIO - MAP errors out due to incorrect MMCM attributes set by the Aurora 8B10B Core

Description

The Aurora 8B10B Core uses 400 as MMCM's VCO lowest frequency limit. This limit increased to 600 MHz based on characterization data for all Virtex-6 and Virtex-6 -1L devices.
MAP errors out for the core that do not meet the VCO frequency range.
Apart from this issue, MAP generates an error for using the values 1, 2, 3 or 4 or fractional values for CLKFBOUT_MULT_F in MMCM_ADV.

Solution

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

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

Aurora 8B10B Core instantiates MMCM component in CLOCK_MODULE. This is present inside <generated core component name>\example_design\clock_module.

The following table shows the Aurora 8B10B core?s clock_module parameters with respect to MMCM attributes:

Clocking Wizard's MMCM

Aurora 8B10B core

Notes

CLKFBOUT_MULT_F

MULT

DIVICLK_DIVIDE

DIVIDE

CLKIN1_PERIOD

CLK_PERIOD

CLKOUT0_DIVIDE_F

OUT0_DIVIDE

CLKOUT1_DIVIDE

OUT1_DIVIDE

CLKOUT2_DIVIDE

OUT2_DIVIDE

This will be used only when two GT REFCLK were used

CLKOUT3_DIVIDE

OUT3_DIVIDE

This will be used only when two GT REFCLK were used

Clocking Wizard requires input frequency (i.e., CLKIN1_FREQ) and output frequency to generate the MMCM component.

Step1: Input frequency calculation

Input frequency is calculated as (Line rate/20)*1000

Line Rate is Aurora 8B10B core's parameter and refers to c_line_rate parameter in XCO file. This value should be entered as Primary input clock frequency in the Clocking Wizard GUI page 1.

Step2: Output frequency1 calculation

For 2-byte Aurora (i.e. c_lane_width value is 2 in XCO): Output frequency1 is same as Primary input clock frequency.

Output frequency1 = ((Line rate/20)*1000) (in MHz)

For 4-byte Aurora (i.e., c_lane_width value is 4 in XCO): Output frequency1 is half rate of the Primary input clock frequency and can be calculated as follows: Output frequency1 = ((Line rate/20)*1000)/2 (in MHz)

This value should be entered as CLK_OUT1 in the Clocking Wizard GUI page 2.

Step3: Output frequency2 calculation
Output frequency2 is same as Primary input clock frequency calculated in Step1:

This value should be entered as CLK_OUT2 in the Clocking Wizard GUI page 2.

CLK_OUT2 check box must be selected.

If Aurora 8B10B uses two GT REFCLKs (i.e. c_gt_clock_2 is having valid value other than 'None' in XCO),

Then follow Step4 and Step5.

Step4: Output frequency3 calculation

Output frequency3 is same as Output frequency1 calculated in Step2.

This value should be entered as CLK_OUT3 in the Clocking Wizard GUI page 2.

CLK_OUT3 check box must be selected.

Step5: Output frequency4 calculation

Output frequency4 is same as Output frequency2 calculated in Step3.

This value should be entered as CLK_OUT4 in Clocking wizard GUI page2.

CLK_OUT4 check box must be selected.

Clocking Wizard displays all MMCM attribute values in GUI page 4 after the above mentioned steps are followed.

The values displayed in GUI page 4 can be used directly to update Aurora 8B10B core's CLOCK_MODULE or Clocking Wizard core's generated template values can be used to update CLOCK_MODULE.

MMCM uses following simplified formula to calculate VCO frequency range:

VCO Frequency = (CLKFBOUT_MULT_F/DIVCLK_DIVIDE)*CLKIN1_FREQ

Use the above formula and the Virtex-6 FPGA Clocking Resources User Guide (UG362) for reference.

AR# 34189
Date Created 03/03/2010
Last Updated 04/12/2010
Status Active
Type General Article
Devices
  • Virtex-6 CXT
  • Virtex-6 LXT
  • Virtex-6 SXT
Tools
  • ISE Design Suite - 11.3
  • ISE Design Suite - 11.4
IP
  • Aurora
  • Aurora 8B/10B