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AR# 41689

13.x - XST generates large DSP cascades only for n taps filters


XST generates large DSP cascades. How can I prevent it?


XST first infers isolated DSP48 and then builds DSP48 chains in a second step. So, XST creates larger DSP chains than the device can accommodate.

To prevent XST from creating these large chains, insert a KEEP constraint between the two successive taps. This can be done through the XCF constraints file, or at the HDL source.

For more information on constraints, refer to the Constraints Guide at: 

AR# 41689
Date Created 04/08/2011
Last Updated 05/23/2014
Status Archive
Type Known Issues
  • Virtex-7
  • Virtex-7 HT
  • Virtex-6 CXT
  • More
  • Virtex-6 HXT
  • Virtex-6 LX
  • Virtex-6 LXT
  • Virtex-6 SXT
  • Virtex-6Q
  • Less