Ensure that you consider the implications of selecting a particular rounding mode on resource utilization. Generally, the FIR Compiler IP core attempts to integrate rounding functions with existing functions, which usually means the accumulator portion of the circuit. However, this is not always possible. In certain combinations of rounding mode, filter type and device family, an additional DSP slice must be used to implement the rounding function. The most important factor to consider is the inherent hardware support for each mode in each of the device families, but filter type and configuration also play a role.
Table: Indicative Table of Hardware Support for Rounding Modes for Particular Filter Types indicates the combinations of filter type and rounding type for which no extra DSP slice is likely to be required. Where all three DSP slice enabled device families are likely to support that combination of rounding mode and filter type without an additional DSP slice, a tick mark is entered; where none of the three is likely to support the combination without the additional DSP slice, a check mark is entered; where there is a list of families provided, the list refers to those families that support the combination without an extra DSP slice. Support for symmetric rounding assumes that either there is a spare cycle available, or approximation is allowed. If this is not the case, an additional DSP slice is always required for symmetric rounding modes, regardless of filter type or family.
Table: Indicative Table of Hardware Support for Rounding Modes for Particular Filter Types is indicative only, and certain combinations for which hardware support is indicated actually require the extra DSP, and vice versa.