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AR# 56180

2013.x - TIMING: Switching Limit Fmin violation when CLKOUT4_CASCADE = "TRUE" in MMCM

Description

When the MMCM is configured in cascade mode for CLKOUT4, the minimum output frequency from this pin should be 36KHz, as per the Datasheet specifications.


However Vivado Timing reports a Switching Limit violation of the output frequency for this pin and it requests a minimum output frequency of 4.69MHz.


This is the standard minimum output frequency but when CLKOUT4_CASCADE = "TRUE", the minimum frequency allowed in CLKOUT4 should be 36KHz.

Is this a problem with the tools?

Solution

Yes, There is a problem with the values included in the Speed file.

When CLKOUT4 is cascaded, the specification for the minimum allowed frequency reported in the datasheet is not included.


In that case the tool uses the standard value 4.69MHz and can issue a Switching Limit violation.


It is safe to ignore this violation if the output frequency meets the requirement.

A request has been filed to fix this in a future release.
AR# 56180
Date Created 05/29/2013
Last Updated 09/02/2014
Status Active
Type Known Issues
Devices
  • Artix-7
  • Kintex-7
  • Virtex-7
Tools
  • Vivado Design Suite - 2013.1