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AR# 24640

LogiCORE FIR Compiler v2.0 - Why can I not use 32 bit coefficients for a MAC FIR?

Description

The FIR Compiler v2.0 does not support MAC FIR implementations in Virtex-4 with coefficient bitwidths above 18-bits, nor is it supported in Virtex-5 with greater than 25-bits. A GUI bug allows users to attempt to generate cores with up to 32 bits of coefficient width, but such cores will fail to generate.

Solution

The following family specific rules should be usd to determine allowable bitwidths in these families: 

 

- Virtex-4 supports unsigned coefficients up to 18 bits for Signed values, or 17-bits for Unsigned values (with the exception of interpolation filters with symmetric coefficients, in which case the limits are 17 bits for Signed and 16 bits for Unsigned).  

- Virtex-5 supports unsigned coefficients up to 25 bits for Signed values, or 24 bits for Unsigned values (with the exception of interpolation filters with symmetric coefficients, in which case the limits are 24 bits for Signed and 23 bits for Unsigned). 

 

These restrictions are due to the bitwidth limitations of the multipliers in the DSP slice.

AR# 24640
Date Created 09/04/2007
Last Updated 05/21/2014
Status Archive
Type General Article