Why wasn't my finite impulse response (FIR) filter implemented in the Stratix™ digital signal processing (DSP) blocks even though I turned on the Use Stratix Dedicated DSP Block check box in the Quartus® II software?

Description

There is a problem in the FIR Compiler version 2.5 that causes FIR filters with certain, small input and/or coefficient bit widths to be implemented in logic elements (LEs) rather than in the Stratix DSP blocks.

As a workaround, you can manually assign the multipliers to the Stratix DSP blocks by performing the following steps:

1. In the project directory, open the file <FIR filter name>_st.v.
2. To implement q multipliers in DSP blocks for module instantiations Umlu_0_n, Umlu_1_n, Umlu_2_n,...,Umlu_q-2_n, and Umlu_q-1_n, find the module instantiation Umlu_x_d, where x is a number between 0 and q-1.
3. Add the following parameter definition to the module instantiation, replacing x with the number in the module instantiation name:
   defparam Umlu_x_n.DSP_USE = "YES";

This problem is currently scheduled to be fixed in a future version of the FIR Compiler.