FIR II IP Core: User Guide

ID 683208
Date 8/14/2023
Document Table of Contents
Give Feedback Using Hard Multiplier Threshold

This FIR II IP core threshold is the trade-off between hard and soft multipliers. For devices that support hard multipliers or DSP blocks, use these resources instead of a soft multiplier made from LEs.
For example, a 2-bit × 10-bit multiplier consumes very few LEs. The hard multiplier threshold value corresponds to the number of LEs that save a multiplier. If the hard multiplier threshold value is 100, you are allowing 100 LEs. Therefore, an 18 × 18 multiplier (that requires approximately 182–350 LEs) does not transfer to LEs because it requires more LEs than the threshold value. However, the IP core implements a 16 × 4 multiplier that requires approximately 64 LEs as a soft multiplier with this setting.
  1. Set the default to always use hard multipliers. With this value, IP core implements a 24 × 18 multiplier as two 18 × 18 multipliers.
  2. Set a value of approximately 300 to keep 18 × 18 multipliers hard, but transform smaller multipliers to LEs. The IP core implements a 24 × 18 multiplier as a 6 × 18 multiplier and an 18 × 18 multiplier, so this setting builds the hybrid multipliers that you require.
  3. Set a value of approximately 1,000 to implement the multipliers entirely as LEs. Essentially, you are allowing a high number (1000) of LEs to save using an 18 × 18 multiplier.
  4. Set a value of approximately 10 to implement a 24 × 16 multiplier as a 36 × 36 multiplier. With the value, you are not even allowing the adder to combine two multipliers. Therefore, the system has to use a 36 × 36 multiplier in a single DSP block.