188.8.131.52. Diagonal Symmetry
The FIR Filter IP has 4 axes of symmetry in the 2D coefficient array across a horizontal line, a vertical line, and 2 diagonal lines through the center tap.
In this case, the number of horizontal taps (N) and the number of vertical taps (M) must be odd, and they must have same value (N = M). Diagonal symmetry offers only Tu = ((N+1)/2) unique coefficient values in either the horizontal or vertical directions, and a total of (Tu*(Tu+1))/2 unique coefficient values.
With run-time control of the coefficients, the register map only includes addresses to update the (Tu *( Tu +1))/2 unique coefficient values, indexed for an example 5×5 array.